This document provides instructions for navigating an electronics learning software. It explains that users can click anywhere on the screen to advance animations or click buttons if present. It also notes to always move the mouse before clicking. The remainder of the document covers various electronics concepts across multiple slides.
The document provides the solution to a physics problem involving two resistors connected in series and parallel configurations. When connected in series, their effective resistance is 3 ohms, and when connected in parallel it is 2/3 ohms. Using these values and equations for series and parallel resistances, the problem determines that the individual resistances of the two resistors are 2 ohms and 1 ohm.
This document provides information about basic circuit diagram symbols and components. It begins with an overview of basic circuit diagrams showing a power source, switch, and load. It then discusses passive electronic components like resistors and capacitors. Resistors are described in detail, including color codes, types, and how resistors behave in series and parallel circuits. Ohm's law and applications like voltage dividers and current dividers are also covered.
This document provides design and assembly instructions for various LED lighting units that can be manufactured locally. It covers basic electrical concepts needed to work with LEDs such as current, voltage, resistors, circuits etc. Several circuit diagrams and instructions are given for making different LED lights - emergency lamps, AC/DC lamps, torches etc. It also includes chapters on power sources like grid, solar and pedal power that can be used to charge batteries and power the lights. Proper tools and safety procedures for assembly are emphasized. The goal is to enable local electricians to make affordable LED lights in their communities.
This document provides an overview of key concepts in electric circuits including:
1. An electric circuit connects an energy source to an energy consuming device through conducting wires that allow electric charges to move. Electromotive force drives current, measured in amperes, through a circuit.
2. Ohm's law defines the relationship between voltage, current, and resistance. Resistance depends on the material's resistivity and dimensions. Components like resistors control current in circuits.
3. Electric power, measured in watts, is calculated by multiplying voltage by current. This relates to the energy delivered by a circuit over time for devices that function as resistors.
Okay, let me solve this step-by-step:
1) System voltage = 24V
2) Current = 8A
3) Distance = 22ft (round trip) = 44ft
4) Allowable voltage drop = 1% of 24V = 0.24V
Using the voltage drop formula:
VD = 2 * distance * current * resistance / 1000
Solving for resistance:
Resistance = (VD * 1000) / (2 * distance * current)
= (0.24 * 1000) / (2 * 44 * 8) = 0.55 ohms/kft
From the wire tables, the smallest wire with resistance less than 0.55 oh
This document discusses electric circuits and Ohm's law. It provides examples of calculating current, resistance, voltage, and power in both series and parallel circuits. Key points covered include:
- Ohm's law defines the relationship between voltage, current, and resistance in a circuit.
- Components in series experience the same current but their voltages add up. The total resistance is the sum of the individual resistances.
- Components in parallel experience the same voltage but their currents combine. The total resistance is lower than any individual resistance.
- Power is calculated as the product of voltage and current, and describes how much energy is used by components in a circuit.
Voltage drop is the voltage lost within an electrical circuit due to the resistance of the conductors. It represents the wasted electricity in a circuit. The maximum allowable voltage drop is typically 3% according to code. Voltage drop can be calculated using formulas involving current, resistance, conductor material, length and size. The NEC provides tables listing the resistance and ampacity of common wire gauges to determine the proper wire size for an electrical circuit.
This document provides a test paper on analog electronics with multiple choice questions and solutions. It begins with an introduction stating it is Test Paper-1 on Analog Electronics from the GATE Multiple Choice Questions ECE source book. It then provides 20 multiple choice questions related to topics in analog electronics like diodes, transistors, op-amps, and filters. Each question is followed by a short solution explaining the reasoning. The questions cover concepts such as diode and transistor biasing, amplifier configurations, filter design, and more.
The document provides the solution to a physics problem involving two resistors connected in series and parallel configurations. When connected in series, their effective resistance is 3 ohms, and when connected in parallel it is 2/3 ohms. Using these values and equations for series and parallel resistances, the problem determines that the individual resistances of the two resistors are 2 ohms and 1 ohm.
This document provides information about basic circuit diagram symbols and components. It begins with an overview of basic circuit diagrams showing a power source, switch, and load. It then discusses passive electronic components like resistors and capacitors. Resistors are described in detail, including color codes, types, and how resistors behave in series and parallel circuits. Ohm's law and applications like voltage dividers and current dividers are also covered.
This document provides design and assembly instructions for various LED lighting units that can be manufactured locally. It covers basic electrical concepts needed to work with LEDs such as current, voltage, resistors, circuits etc. Several circuit diagrams and instructions are given for making different LED lights - emergency lamps, AC/DC lamps, torches etc. It also includes chapters on power sources like grid, solar and pedal power that can be used to charge batteries and power the lights. Proper tools and safety procedures for assembly are emphasized. The goal is to enable local electricians to make affordable LED lights in their communities.
This document provides an overview of key concepts in electric circuits including:
1. An electric circuit connects an energy source to an energy consuming device through conducting wires that allow electric charges to move. Electromotive force drives current, measured in amperes, through a circuit.
2. Ohm's law defines the relationship between voltage, current, and resistance. Resistance depends on the material's resistivity and dimensions. Components like resistors control current in circuits.
3. Electric power, measured in watts, is calculated by multiplying voltage by current. This relates to the energy delivered by a circuit over time for devices that function as resistors.
Okay, let me solve this step-by-step:
1) System voltage = 24V
2) Current = 8A
3) Distance = 22ft (round trip) = 44ft
4) Allowable voltage drop = 1% of 24V = 0.24V
Using the voltage drop formula:
VD = 2 * distance * current * resistance / 1000
Solving for resistance:
Resistance = (VD * 1000) / (2 * distance * current)
= (0.24 * 1000) / (2 * 44 * 8) = 0.55 ohms/kft
From the wire tables, the smallest wire with resistance less than 0.55 oh
This document discusses electric circuits and Ohm's law. It provides examples of calculating current, resistance, voltage, and power in both series and parallel circuits. Key points covered include:
- Ohm's law defines the relationship between voltage, current, and resistance in a circuit.
- Components in series experience the same current but their voltages add up. The total resistance is the sum of the individual resistances.
- Components in parallel experience the same voltage but their currents combine. The total resistance is lower than any individual resistance.
- Power is calculated as the product of voltage and current, and describes how much energy is used by components in a circuit.
Voltage drop is the voltage lost within an electrical circuit due to the resistance of the conductors. It represents the wasted electricity in a circuit. The maximum allowable voltage drop is typically 3% according to code. Voltage drop can be calculated using formulas involving current, resistance, conductor material, length and size. The NEC provides tables listing the resistance and ampacity of common wire gauges to determine the proper wire size for an electrical circuit.
This document provides a test paper on analog electronics with multiple choice questions and solutions. It begins with an introduction stating it is Test Paper-1 on Analog Electronics from the GATE Multiple Choice Questions ECE source book. It then provides 20 multiple choice questions related to topics in analog electronics like diodes, transistors, op-amps, and filters. Each question is followed by a short solution explaining the reasoning. The questions cover concepts such as diode and transistor biasing, amplifier configurations, filter design, and more.
This document provides strategies and tips for taking the NABCEP PV Installer exam, including:
- An explanation of the "120-Rule" for sizing overcurrent protection devices and calculating maximum inverter output.
- Recommendations for last-minute study resources focusing on code articles and questions/answers.
- Suggestions for effective test-taking strategies like circling question types, using provided formulas, and time management to complete all questions in the allotted time.
- Details on what to expect on exam day including available materials, security procedures, and focusing amid distractions.
#SolarMOOC Random Problems from 2009 NABCEP STUDY GUIDEsolpowerpeople
The key aspects here are:
- NEC 690.8(A)(4) specifies requirements for stand-alone inverter input circuits
- It states the maximum current shall be the stand-alone continuous inverter input current rating
- This input current rating is provided by the inverter manufacturer
- The question asks for the minimum ampacity, so we would size the conductors to the inverter input rating
Therefore, the minimum ampacity of the conductors connecting the battery bank to a stand-alone inverter would be the continuous inverter input current rating as specified by the manufacturer.
The answer is a.
This document discusses problems applying Ohm's law and Watt's law. It begins by explaining color codes used for resistors and introduces the protoboard, a tool used for prototyping circuits. Examples are given of calculating resistance, voltage, and power using Ohm's and Watt's laws. The conclusion reiterates that a protoboard allows modifying circuits easily and color codes determine resistor values. Problems demonstrate computations for resistance, voltage, current, and power.
EXPERIMENT 2 : resistor colour codes and diodesYong Ying
This experiment had two parts:
1) Determine resistor values using color codes, digital ohmmeter, and analog ohmmeter. Readings from different meters were recorded in a table.
2) Identify anode, cathode, built-in voltage, and material of diodes. Readings from digital and analog meters for different diodes were recorded in another table. Built-in voltages helped identify materials as silica or other. Proper connection of anode and cathode was needed for readings and LED operation.
The conclusion was that resistor readings should match color codes, and checking built-in voltage can identify diode materials. Connection orientation is important for measurements and LED function.
Internal Resistance, EMF and Oscilloscopes.pptmrmeredith
The document discusses internal resistance of batteries, electromotive force (EMF), and using an oscilloscope to measure voltage and frequency. It explains that batteries have internal resistance that causes voltage to drop as current increases. EMF is defined as the voltage produced without any current flow. An oscilloscope can be used to measure the voltage and frequency of alternating current (AC) signals. Examples are given of measuring battery parameters and mains voltage.
The document discusses different types of basic electronic elements, focusing on resistors. It describes what resistors are, their main characteristics like resistance and tolerance, common units like ohms, and methods to read resistor color codes or alphanumeric codes to determine resistance values. It also covers variable resistors like potentiometers that can adjust voltage levels.
PROBLEMAS RESUELTOS (93) DE LABORATORIO N° 2 DE FÍSICA II - SEARSLUIS POWELL
This document discusses direct-current circuits and series-parallel resistor combinations. It contains several examples of calculating equivalent resistances and currents in circuits with series and parallel resistors. The key steps are to identify the resistor combinations, set up the appropriate series or parallel resistance formula, then execute the calculations and evaluate the results. Calculating power dissipation in resistors is also demonstrated.
1. Cells connected in series have their emfs add up but their currents remain equal. Cells in parallel have the same emf but their currents divide.
2. The internal resistance of cells in series adds up while the reciprocal of the internal resistance adds up for parallel cells.
3. A mixed grouping of cells has some cells in series forming rows, and the rows in parallel. The total resistance is minimized when the rows' resistance equals the series resistance within rows.
This lab report summarizes two experiments measuring resistance and voltage. In the first experiment, the resistance of three resistors was calculated from color codes and measured with a multimeter, finding errors within 5%. The second experiment measured voltages from a power supply at increasing levels, finding small discrepancies between the power supply and multimeter readings due to internal resistance converting energy. Overall, the lab demonstrated that calculating resistance from color codes is reasonably accurate and introduced concepts of resistance, voltage measurement, and energy conversion in circuits.
#Solar mooc 2009 nabcep study guide solutions 1-29solpowerpeople
The document provides answers and explanations to 29 questions from the April 2009 NABCEP Study Guide. The questions cover topics related to PV installation safety such as electrical safety, fall protection, ladders, PPE, battery safety, and NEC requirements. The responses reference the relevant sections of the NABCEP Study Guide and provide brief explanations or code references to support the answers.
1. This document describes an experiment to identify resistor color codes and verify Ohm's Law. It includes objectives, equipment, procedures, and questions.
2. The first part explains how to determine a resistor's value and tolerance from its color bands. Tables list the color codes used in 4-band and 5-band resistors.
3. The second part tests Ohm's Law by measuring the current through resistors under different voltages. A circuit is assembled and current is measured both ways through each resistor to verify the relationships defined by Ohm's Law.
The document defines internal resistance as the electrical resistance inside batteries and power supplies that causes some energy to be wasted as heat. It provides equations relating internal resistance (r), electromotive force (EMF, E), current (I), and terminal voltage (V). Examples are given of using Kirchhoff's laws and these equations to calculate internal resistance, EMF and voltages for circuits with batteries and resistors. An experiment for determining internal resistance by varying resistance and measuring voltage and current is described.
This document describes diode circuits and their applications. It begins with an overview of ideal, constant voltage, and exponential diode models. It then covers half-wave and full-wave rectification used in applications like phone chargers. The document also discusses limiter circuits, small signal analysis around operating points, and using incremental resistance to simplify nonlinear circuit analysis. Key applications of diodes in rectification, signal strength indicators, and logic gates are presented.
The document defines electromotive force (e.m.f) as the work done by a source to drive one coulomb of charge around a complete circuit. It states that the e.m.f of a cell or battery refers to the electrical energy produced for each coulomb that passes through it. However, the potential difference, or voltage, across the external terminals is usually lower than the e.m.f due to the internal resistance of the cell or battery, which causes a drop in potential and some of the energy to be lost as heat. The relationship between e.m.f, potential difference, current, and internal resistance is explained.
The document provides an overview schedule and learning objectives for an electronics workshop. The schedule includes installing Arduino software, an introduction to electronics theory, working on practical Arduino projects, and individual consultations. The objectives are to learn basics of electronics, the Arduino programming language, prototyping methods, and how to convert analog to digital values and vice versa. The document then provides primers on various electronics concepts like digital vs analog, Ohm's law, voltage, current, resistance, components, signals, design patterns, and discusses topics like charlieplexing, PWM, and sensors/actuators.
Resistors are the most common electronic component and come in various materials and ratings. They control current flow through a circuit based on Ohm's law. Resistors are rated by their resistance value in ohms, power handling ability in watts, and tolerance level in percentages. Low power resistors are color coded for easy identification of their resistance values.
The document summarizes key concepts about electric circuits, including:
- An electric circuit connects an energy source to a device using conducting wires for electric charge to flow. Current is the rate of charge flow.
- Ohm's law defines the relationship between voltage, current, and resistance in a circuit. Resistance depends on the material's resistivity, length, and cross-sectional area.
- Power in a circuit is defined as the product of voltage and current. It describes the rate at which energy is transferred by the electric current.
- Circuits can have components connected in series, parallel, or a combination. Kirchhoff's laws describe the analysis of current and voltage in such circuits.
This document provides instructions for assembling various LED lighting units using basic electric components. It begins with an introduction to LEDs and their advantages over other light sources. It then covers basic electric concepts such as current, voltage, resistors, capacitors, diodes and circuits. Finally, it provides circuits and instructions for different LED light units including an emergency lamp, various battery-powered lamps, LED strips, and systems involving microcontrollers or solar/pedal power. The goal is to educate local electricians on assembling affordable, efficient LED lights.
This lab report summarizes two experiments measuring resistance and voltage. In the first experiment, the resistance of three resistors was calculated from their color codes and measured with a digital multimeter. The measured values were within 5% of the calculated values, validating the accuracy of using color codes. In the second experiment, the voltage output of a power supply was measured at increasing levels and found to be slightly lower than the power supply readings due to internal resistance dropping voltage. The experiments helped familiarize the student with lab equipment and electrical measurements.
Here are the key steps to solve series-parallel circuits:
1) Identify series and parallel sections
2) Use series/parallel rules within each section
3) Connect the sections using KVL and KCL
Let me know if any part of the process is unclear! Solving complex circuits takes practice.
This document provides an overview of electrical and electronic systems, quantities, units, and safety. It discusses:
1) Systems are groups of interrelated parts that perform a specific function via inputs and outputs. Electrical systems deal with electric power, electronic systems deal with signals.
2) Important units include the volt, ampere, ohm, watt, and engineering prefixes like milli, mega and giga. Metric conversions and rounding rules are also covered.
3) Circuit components like resistors, switches, and meters are described. Resistor color codes, variable resistors, and schematic symbols are discussed. Basic electric circuits, current, resistance and safety guidelines are summarized.
This document provides strategies and tips for taking the NABCEP PV Installer exam, including:
- An explanation of the "120-Rule" for sizing overcurrent protection devices and calculating maximum inverter output.
- Recommendations for last-minute study resources focusing on code articles and questions/answers.
- Suggestions for effective test-taking strategies like circling question types, using provided formulas, and time management to complete all questions in the allotted time.
- Details on what to expect on exam day including available materials, security procedures, and focusing amid distractions.
#SolarMOOC Random Problems from 2009 NABCEP STUDY GUIDEsolpowerpeople
The key aspects here are:
- NEC 690.8(A)(4) specifies requirements for stand-alone inverter input circuits
- It states the maximum current shall be the stand-alone continuous inverter input current rating
- This input current rating is provided by the inverter manufacturer
- The question asks for the minimum ampacity, so we would size the conductors to the inverter input rating
Therefore, the minimum ampacity of the conductors connecting the battery bank to a stand-alone inverter would be the continuous inverter input current rating as specified by the manufacturer.
The answer is a.
This document discusses problems applying Ohm's law and Watt's law. It begins by explaining color codes used for resistors and introduces the protoboard, a tool used for prototyping circuits. Examples are given of calculating resistance, voltage, and power using Ohm's and Watt's laws. The conclusion reiterates that a protoboard allows modifying circuits easily and color codes determine resistor values. Problems demonstrate computations for resistance, voltage, current, and power.
EXPERIMENT 2 : resistor colour codes and diodesYong Ying
This experiment had two parts:
1) Determine resistor values using color codes, digital ohmmeter, and analog ohmmeter. Readings from different meters were recorded in a table.
2) Identify anode, cathode, built-in voltage, and material of diodes. Readings from digital and analog meters for different diodes were recorded in another table. Built-in voltages helped identify materials as silica or other. Proper connection of anode and cathode was needed for readings and LED operation.
The conclusion was that resistor readings should match color codes, and checking built-in voltage can identify diode materials. Connection orientation is important for measurements and LED function.
Internal Resistance, EMF and Oscilloscopes.pptmrmeredith
The document discusses internal resistance of batteries, electromotive force (EMF), and using an oscilloscope to measure voltage and frequency. It explains that batteries have internal resistance that causes voltage to drop as current increases. EMF is defined as the voltage produced without any current flow. An oscilloscope can be used to measure the voltage and frequency of alternating current (AC) signals. Examples are given of measuring battery parameters and mains voltage.
The document discusses different types of basic electronic elements, focusing on resistors. It describes what resistors are, their main characteristics like resistance and tolerance, common units like ohms, and methods to read resistor color codes or alphanumeric codes to determine resistance values. It also covers variable resistors like potentiometers that can adjust voltage levels.
PROBLEMAS RESUELTOS (93) DE LABORATORIO N° 2 DE FÍSICA II - SEARSLUIS POWELL
This document discusses direct-current circuits and series-parallel resistor combinations. It contains several examples of calculating equivalent resistances and currents in circuits with series and parallel resistors. The key steps are to identify the resistor combinations, set up the appropriate series or parallel resistance formula, then execute the calculations and evaluate the results. Calculating power dissipation in resistors is also demonstrated.
1. Cells connected in series have their emfs add up but their currents remain equal. Cells in parallel have the same emf but their currents divide.
2. The internal resistance of cells in series adds up while the reciprocal of the internal resistance adds up for parallel cells.
3. A mixed grouping of cells has some cells in series forming rows, and the rows in parallel. The total resistance is minimized when the rows' resistance equals the series resistance within rows.
This lab report summarizes two experiments measuring resistance and voltage. In the first experiment, the resistance of three resistors was calculated from color codes and measured with a multimeter, finding errors within 5%. The second experiment measured voltages from a power supply at increasing levels, finding small discrepancies between the power supply and multimeter readings due to internal resistance converting energy. Overall, the lab demonstrated that calculating resistance from color codes is reasonably accurate and introduced concepts of resistance, voltage measurement, and energy conversion in circuits.
#Solar mooc 2009 nabcep study guide solutions 1-29solpowerpeople
The document provides answers and explanations to 29 questions from the April 2009 NABCEP Study Guide. The questions cover topics related to PV installation safety such as electrical safety, fall protection, ladders, PPE, battery safety, and NEC requirements. The responses reference the relevant sections of the NABCEP Study Guide and provide brief explanations or code references to support the answers.
1. This document describes an experiment to identify resistor color codes and verify Ohm's Law. It includes objectives, equipment, procedures, and questions.
2. The first part explains how to determine a resistor's value and tolerance from its color bands. Tables list the color codes used in 4-band and 5-band resistors.
3. The second part tests Ohm's Law by measuring the current through resistors under different voltages. A circuit is assembled and current is measured both ways through each resistor to verify the relationships defined by Ohm's Law.
The document defines internal resistance as the electrical resistance inside batteries and power supplies that causes some energy to be wasted as heat. It provides equations relating internal resistance (r), electromotive force (EMF, E), current (I), and terminal voltage (V). Examples are given of using Kirchhoff's laws and these equations to calculate internal resistance, EMF and voltages for circuits with batteries and resistors. An experiment for determining internal resistance by varying resistance and measuring voltage and current is described.
This document describes diode circuits and their applications. It begins with an overview of ideal, constant voltage, and exponential diode models. It then covers half-wave and full-wave rectification used in applications like phone chargers. The document also discusses limiter circuits, small signal analysis around operating points, and using incremental resistance to simplify nonlinear circuit analysis. Key applications of diodes in rectification, signal strength indicators, and logic gates are presented.
The document defines electromotive force (e.m.f) as the work done by a source to drive one coulomb of charge around a complete circuit. It states that the e.m.f of a cell or battery refers to the electrical energy produced for each coulomb that passes through it. However, the potential difference, or voltage, across the external terminals is usually lower than the e.m.f due to the internal resistance of the cell or battery, which causes a drop in potential and some of the energy to be lost as heat. The relationship between e.m.f, potential difference, current, and internal resistance is explained.
The document provides an overview schedule and learning objectives for an electronics workshop. The schedule includes installing Arduino software, an introduction to electronics theory, working on practical Arduino projects, and individual consultations. The objectives are to learn basics of electronics, the Arduino programming language, prototyping methods, and how to convert analog to digital values and vice versa. The document then provides primers on various electronics concepts like digital vs analog, Ohm's law, voltage, current, resistance, components, signals, design patterns, and discusses topics like charlieplexing, PWM, and sensors/actuators.
Resistors are the most common electronic component and come in various materials and ratings. They control current flow through a circuit based on Ohm's law. Resistors are rated by their resistance value in ohms, power handling ability in watts, and tolerance level in percentages. Low power resistors are color coded for easy identification of their resistance values.
The document summarizes key concepts about electric circuits, including:
- An electric circuit connects an energy source to a device using conducting wires for electric charge to flow. Current is the rate of charge flow.
- Ohm's law defines the relationship between voltage, current, and resistance in a circuit. Resistance depends on the material's resistivity, length, and cross-sectional area.
- Power in a circuit is defined as the product of voltage and current. It describes the rate at which energy is transferred by the electric current.
- Circuits can have components connected in series, parallel, or a combination. Kirchhoff's laws describe the analysis of current and voltage in such circuits.
This document provides instructions for assembling various LED lighting units using basic electric components. It begins with an introduction to LEDs and their advantages over other light sources. It then covers basic electric concepts such as current, voltage, resistors, capacitors, diodes and circuits. Finally, it provides circuits and instructions for different LED light units including an emergency lamp, various battery-powered lamps, LED strips, and systems involving microcontrollers or solar/pedal power. The goal is to educate local electricians on assembling affordable, efficient LED lights.
This lab report summarizes two experiments measuring resistance and voltage. In the first experiment, the resistance of three resistors was calculated from their color codes and measured with a digital multimeter. The measured values were within 5% of the calculated values, validating the accuracy of using color codes. In the second experiment, the voltage output of a power supply was measured at increasing levels and found to be slightly lower than the power supply readings due to internal resistance dropping voltage. The experiments helped familiarize the student with lab equipment and electrical measurements.
Here are the key steps to solve series-parallel circuits:
1) Identify series and parallel sections
2) Use series/parallel rules within each section
3) Connect the sections using KVL and KCL
Let me know if any part of the process is unclear! Solving complex circuits takes practice.
This document provides an overview of electrical and electronic systems, quantities, units, and safety. It discusses:
1) Systems are groups of interrelated parts that perform a specific function via inputs and outputs. Electrical systems deal with electric power, electronic systems deal with signals.
2) Important units include the volt, ampere, ohm, watt, and engineering prefixes like milli, mega and giga. Metric conversions and rounding rules are also covered.
3) Circuit components like resistors, switches, and meters are described. Resistor color codes, variable resistors, and schematic symbols are discussed. Basic electric circuits, current, resistance and safety guidelines are summarized.
1) The document discusses key concepts in electrical systems including systems, inputs/outputs, circuits, voltage, current, resistance, and measurement devices.
2) It defines important units like volts, amps, and ohms and describes metric prefixes for large and small units.
3) Safety tips are provided for working with electrical circuits including maintaining a clean workspace and knowing emergency procedures.
The document provides instructions for a Grade 10 General examination on Fundamentals of Electronics. It outlines 4 sections covering electrical circuits, resistors, electronic calculations, and embedded systems. Students must have a blue ink pen, pencil, ruler, and calculator (if required) and are not allowed electronic devices. The exam consists of multiple choice, true/false, short answer, and matching questions worth a total of 50 marks over 35 minutes.
The document provides instructions for a Grade 10 Advanced electronics exam. It outlines the sections and topics that will be covered in the exam, including electrical circuits, resistors, electronic calculations, and embedded systems. Students are instructed to bring specific materials to the exam and are informed that electronic devices are not allowed. The exam will consist of multiple choice questions, true/false statements, short answer questions, diagrams and a matching task testing knowledge over a total time of 35 minutes.
This document provides an outline for a course on electromagnetism, electricity, and digital electronics. It covers topics such as the theory of electrons and electricity, resistors, Ohm's law, electric circuits, the theory of magnetism, diodes, logic gates, and flip-flops. It lists several textbooks that will be used as references. It then delves into some of the topics in more detail, including the structure of atoms, types of insulators and conductors, direct and alternating current, voltage, current, resistance, and Ohm's law. It also discusses magnetism, electromagnetism, and provides examples of devices that use magnets.
This document provides an outline for a course on electromagnetism, electricity, and digital electronics. It covers topics such as the theory of electrons and electricity, resistors, Ohm's law, electric circuits, theory of magnetism, diodes, logic gates, and combinational and sequential circuits. It lists textbooks that will be used and provides examples and exercises to help teach the concepts.
This document provides an outline for a course on electromagnetism, electricity, and digital electronics. The course covers topics such as the theory of electrons and electricity, resistors, Ohm's law, electric circuits, theory of magnetism, diodes, logic gates, and combinational and sequential circuits. It lists textbooks that will be used as references. The document also provides detailed explanations of concepts in atomic structure, electricity, circuits, electromagnetism, and electronics.
This document discusses electronic components and materials, focusing on resistors and capacitors. It provides information on:
- The basic functions and types of resistors, including fixed resistors like carbon and metal film, as well as variable resistors. It describes how to read resistor color codes and calculate resistance values.
- The basic principle of how capacitors store and discharge electric charge based on capacitance, voltage, and dielectric material. It gives the equations for calculating capacitance and energy storage.
- Common capacitor types including mica, ceramic, electrolytic, and variable capacitors. It explains how capacitance depends on plate area, distance, and dielectric constant.
This document provides an overview of basic electronics components and circuits. It begins with an introduction to passive components like resistors, capacitors, inductors, and transformers. It then covers analog circuits using transistors and operational amplifiers. The document provides details on circuit analysis and different types of filters. It explains concepts like resistors, capacitors, inductors, diodes, transistors, and operational amplifiers. Examples of common circuits are also presented like voltage dividers, rectifiers, and amplifiers.
factors affecting internal resistance/emf of the cellYogesh Baghel
This document discusses internal resistance, electromotive force (EMF), and using an oscilloscope to measure voltage and frequency from a signal generator. It explains how to create batteries from lemons and measure their internal resistance. It also covers how oscilloscopes can be used as voltmeters to measure DC and AC voltage, and how they can measure frequency. The document contains questions about batteries, internal resistance, EMF, RMS voltage, AC power, and using an oscilloscope.
The document defines linear and nonlinear elements, active and passive elements, and unilateral and bilateral elements in electric circuits. It introduces Ohm's law, which states that current is directly proportional to voltage and inversely proportional to resistance. Kirchhoff's laws are also summarized: Kirchhoff's current law states that the algebraic sum of currents at a node is zero, and Kirchhoff's voltage law states that the algebraic sum of voltages in a closed loop is zero. An example circuit is also solved using these laws and Ohm's law to find currents and voltages.
This document discusses Ohm's law and basic circuit concepts. It defines key terms like voltage, current, resistance, power, and energy. It explains that voltage is directly proportional to current based on Ohm's law. Circuits can be connected in series or parallel, and examples show how to calculate current, voltage, resistance, and power in different circuit configurations using Ohm's law.
1. This unit covers basic electrical concepts including charge, current, energy, power, voltage, resistors and circuits. It defines key terms and formulas for calculations.
2. Resistors are introduced as circuit elements that limit current. Different types are described including fixed, variable, and those identified by color codes.
3. Kirchhoff's laws and Thevenin's theorem are presented as methods for analyzing circuits to calculate current, voltage, resistance and simplify complex networks.
The document summarizes an experiment on analyzing series and parallel RLC circuits. It describes:
1) Calculating the theoretical resonance frequency of a series RLC circuit as 18.8 kHz, but measuring it experimentally as 16.73 kHz, a difference of 11.1%.
2) Plotting the output voltage versus frequency, which reaches a minimum at the theoretical resonance point.
3) Analyzing the phase relationship and impedance characteristics at resonance, finding the voltage and current are in phase.
Resistors are the most common electronic component and come in various materials and ratings. They control current flow through a circuit based on Ohm's law. Resistors are rated by their resistance value in ohms, power handling ability in watts, and tolerance level in percentages. Low power resistors are color coded for easy identification of their resistance values. Circuit designers must choose resistors that match the needed resistance, power, tolerance, and other specifications for proper circuit operation.
This document summarizes an experiment to verify Ohm's law and analyze resistive circuits. The experiment has two parts: 1) Develop a voltage-current characteristic curve for a resistor to verify Ohm's law. Measure voltage and current at increasing voltage levels and plot the relationship. 2) Determine voltages and currents in series and parallel resistor circuits using voltage and current divider rules. Measure voltages across individual resistors in series to verify calculations match measurements.
Electric vehicle and photovoltaic advanced roles in enhancing the financial p...IJECEIAES
Climate change's impact on the planet forced the United Nations and governments to promote green energies and electric transportation. The deployments of photovoltaic (PV) and electric vehicle (EV) systems gained stronger momentum due to their numerous advantages over fossil fuel types. The advantages go beyond sustainability to reach financial support and stability. The work in this paper introduces the hybrid system between PV and EV to support industrial and commercial plants. This paper covers the theoretical framework of the proposed hybrid system including the required equation to complete the cost analysis when PV and EV are present. In addition, the proposed design diagram which sets the priorities and requirements of the system is presented. The proposed approach allows setup to advance their power stability, especially during power outages. The presented information supports researchers and plant owners to complete the necessary analysis while promoting the deployment of clean energy. The result of a case study that represents a dairy milk farmer supports the theoretical works and highlights its advanced benefits to existing plants. The short return on investment of the proposed approach supports the paper's novelty approach for the sustainable electrical system. In addition, the proposed system allows for an isolated power setup without the need for a transmission line which enhances the safety of the electrical network
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The Python for beginners. This is an advance computer language.
Electronics
1. Electronics Use your mouse to move around
the software. You can either
click anywhere on the screen to
get the next animation or click
on a button if you can see one on
the screen.
Always move the mouse before
you click it.
ã TPS 1
2002
2. 2
Electronics
Introduction
Ohm’s Law
Power Calculations
Resistors in Series and Parallel
Capacitors
Alternating Current
Waveforms
The Potential Divider
Transistor Circuits
Questions
4. 4
Basic Concepts
Return previous slide
Electric current is due to the flow of charge.
In a solid conductor, the charge is carried by electrons.
In a solid conductor, an electric current is due to the flow
of electrons.
5. 5
Basic Concepts
Return previous slide
Conductors include:
copper
gold
silver
lead
All metals
And water (not distilled) which is why you should not use mains
appliances in the presence of water.
6. 6
Basic Concepts
Return previous slide
Insulators include:
Rubber
Plastic
Most solid non metals
Glass
Glass, unless it is very hot, is one of the best insulators available.
7. Electric current (I) is measured in ampere (A) - I is the symbol used to
indicate current.
The “amp” is a rather large unit for most electronic applications so we
use the following sub-multiples:
1 mA = 0.001A that is 1 / 1 000 th of an ampere
You already know that 1mm is 1/1000th of an metre so there is nothing
7
Basic Concepts
Return previous slide
new here.
1 mA = 0.000 001A that is 1 / 1 000 000 th of an ampere
8. Common sub-multiples of the volt (less than a volt) include:
8
Basic Concepts
Return previous slide
Voltage is measured in volt (V)
1 mV = 0.001V that is 1 / 1 000 th of a volt
1 mV = 0.000 001V that is 1 / 1 000 000 th of a volt
Common multiples of the volt (greater than a volt) include:
1 kV = 1 000 V
1 MV = 1 000 000 V
The kV and the MV are not common in electronics.
9. Common sub-multiples of the ohm (less than an ohm) include:
9
Basic Concepts
Return previous slide
Resistance is measured in ohm (W)
1 m W = 0.001 W that is 1 / 1 000 th of an ohm
1 m W = 0.000 001 W that is 1 / 1 000 000 th of an ohm
This is pronounced micro ohm
Common multiples of the ohm (greater than an ohm) include:
1 k W = 1 000 W
1 M W = 1 000 000 W
The mW and the m W are not common in electronics.
10. Common sub-multiples of the farad (less than a farad) include:
10
Basic Concepts
Return previous slide
Capacitance is measured in farad (F)
1 m F = 0.001 F that is 1 / 1 000 th of a farad
1 m F = 0.000 001 F that is 1 / 1 000 000 th of a farad
1 n F = 0.000 000 001 F that is 1 / 1 000 000 000 th of a farad
this is written in full as a nano farad
1 p F = 0.000 000 000 001 F that is 1 / 1 000 000 000 000 th of a farad
This is written in full as pico farad
11. Here is a summary of many of the available multiples and sub-multiples
Symbol Prefix Multiplication factor
T tera 1012 1 000 000 000 000
G giga 109 1 000 000 000
M mega 106 1 000 000
k kilo 103 1 000
h hecto 102 100
da deca 101 10
d deci 10-1 0.1
c centi 10-2 0.01
m milli 10-3 0.001
m micro 10-6 0.000 001
n nano 10-9 0.000 000 001
p pico 10-12 0.000 000 000 001
f femto 10-15 0.000 000 000 000 001
a atto 10-18 0.000 000 000 000 000 001
The most
frequently used
are in bold.
11
Basic Concepts
Return previous slide
12. This gold band indicates that the tolerance
of the resistor is ±5% (plus or minus 5 percent).
This means that its resistance is between 3 400 W
and 3 800 W. We say it is nominally 3 600 W.
The third band is red. This means that there are 2
zeros.
The second band is blue. This means the second digit is 6.
12
Return previous slide
Basic Concepts
Resistors are marked with a series of coloured rings to give us an idea of
how big their resistance is.
The first band is orange. This means the first digit is
3.
So the resistor is nominally 3 600 W.or 3k6
13. The colours used for the first three bands and their meanings are as
follows:
Colour Number Number of zeros
Black 0 none
Brown 1 0
Red 2 00
Orange 3 000
Yellow 4 0 000
Green 5 00 000
Blue 6 000 000
Violet 7 0 000 000
Grey 8 00 000 000
White 9 000 000 000
13
Basic Concepts
Return previous slide
14. The colours used for the last band and their meanings are as follows:
Gold ± 5 %
Silver ± 10 %
No band ± 20 %
Resistors are manufactured in “preferred values”. That
means that you can only buy certain values.
The preferred values for resistors with a tolerance of
±20% are: 10,15,22,33,47,68 and 100. These are just
the first two significant figures. You can buy a 1500W
but not a 2000 W.
14
Basic Concepts
Return previous slide
17. 17
Basic Concepts
In summary:
Voltage is measured in
Current is measured in
Resistance is measured in
Capacitance is measured in
Volt (V)
Ampere (A)
ohm (W)
farad (F)
3MV = 3 000 000 V
2kV = 2 000 V
5mV = 0.005 A
7mA = 0.000 007 A
& 1nF = 0.000 000 001 F
Home
1pF = 0.000 000 000 001 F
Return previous slide
18. This is called a block diagram.
•The processor is the decision-making part of the system.
•The input is a sensor that transforms everyday phenomena such as
temperature and heat to an electric signal that the processor can deal
with.
•The output is a device that converts an electric signal from the processor
into something that we want.
18
Simple Circuits
Simple circuits have three main blocks of components in common that
perform the same type of job. These are:
Input Processor Output
Return to menu slide
19. 19
Simple Circuits
Simple circuits have three main blocks of components in common that
perform the same type of job. These are:
Input Processor Output
Return to previous slide
Examples of input devices include:
Pressure pads
LDRs
Thermistors
Reed switches
20. 20
Simple Circuits
Simple circuits have three main blocks of components in common that
perform the same type of job. These are:
Input Processor Output
Return to previous slide
Examples of output devices include:
Lamps
LEDs
Motors
Solenoids
21. 21
Simple Circuits
Simple circuits have three main blocks of components in common that
perform the same type of job. These are:
Input Processor Output
Return to previous slide
Examples of basic processors include:
Transistors
Operational amplifiers
22. 22
Simple Circuits
Home
Simple circuits have three main blocks of components in common that
perform the same type of job. These are:
Input Processor Output
What would the block diagram look like for a system that brought on a
light when it got dark?
LDR Processor Lamp
Return to previous slide
23. Questions - Simple Circuits
1 Write down the units of voltage, capacitance, resistance and
current. What is the symbol for current?
2 Write out 22mA and 420 pF in full.
3 Give three examples of input devices.
4 Write out a block circuit diagram for a device that could lift up a
trap door when a beam of light was broken.
5 What is the nominal value and tolerance of this resistor?
6 What would the colours of a 47MW resistor be?
23
ANSWER
ANSWER
ANSWER
ANSWER
ANSWER
ANSWER
Return to menu slide
24. Solutions - Simple Circuits
1 Write down the units of voltage, capacitance, resistance and
current. What is the symbol for current?
24
Voltage volt (V)
Capacitance farad (F)
Resistance ohm (W)
Current ampere (A)
The symbol for current is I
Return
25. Solutions - Simple Circuits
25
2 Write out 22mA and 420 pF in full.
22mA = 22 x 0.001 A = 0 . 22 A
420 pF = 420 x 0.000 000 000 001 F = 0 . 000 000 000 42 F
Return
26. Solutions - Simple Circuits
26 Return
3 Give three examples of input devices.
Pressure pads
LDRs
Thermistors
Reed switches
27. Solutions - Simple Circuits
4 Write out a block circuit diagram for a device that could lift up a
trap door when a beam of light was broken.
LDR Processor Motor
27
or
LDR Processor Solenoid
Note that a bulb is not an input device as it gives out light.
Return
28. Solutions - Simple Circuits
5 What is the nominal value and tolerance of this resistor?
This gold band indicates that the tolerance
of the resistor is ±5% (plus or minus 5 percent).
The third band is red. This means that there are 2
zeros.
The second band is black. This means the second digit is 0.
The first band is brown. This means the first digit is 1.
28
So the resistor is nominally 1 200 W.
Return
29. Solutions - Simple Circuits
6 What would the colours of a 47MW resistor be?
The third band is blue. This means that there are 6 zeros.
The second band is violet. This means the second digit is 7.
The first band is yellow. This means the first digit is 4.
29
The resistor is nominally 47 000 000 W.
This gold band indicates that the tolerance
of the resistor is ±5% (plus or minus 5 percent).
Return
30. 30
Ohm’s Law
Ohm’s Law states that so long as the physical conditions remain
constant, the current through a conductor is proportional to the voltage
across it.
This gives us the formula:
Voltage = current x resistance
V = I R
We can rearrange this equation to give either
R = V / I
or
I = V / R
Return to menu slide
31. 31
Ohm’s Law
What does it mean?
“Physical conditions remaining constant” - This really means as long
as the temperature remains constant. Usually it does.
“The current through a conductor is proportional to the voltage across
it” - this means that if you double the voltage, you get twice the
current. Triple the voltage and you triple the current etc.
Voltage
Current
Low resistance
High resistance
Return previous slide
32. 32
Ohm’s Law
Return previous slide
Calculations using Ohm’s law fall into three types:
What is the resistance
What is the current
if ?
if ?
What is the voltage
(Use R = V / I) if ? (Use V = I x R)
E.G.
What resistance could
you use with a 10V
supply to limit the
current to 15mA?
R = V / I = 10 / 0.015
667 W so use 680 W
(Use I = V / R)
E.G.
A 430 W resistor
protects an LED in a
5V circuit. What is
the current through
the LED?
I = V / R = 5 / 430
= 12 mA
E.G.
12mA runs through
a prorctive resistor
of resistance 820 W.
What is the voltage
across the resistor ?
V = IR = 0.012x820
= 9.84 V
33. The voltage across the diode is 0.7
V and the cell produces 1.5 V.
What is the current through the
resistor?
0.7 V
820 W Diode
If you can’t see how to do it straight away, write the values
given onto the diagram.
33
Ohm’s Law
Return previous slide
1.5V
Voltage across the resistor = 1.5V (provided by the cell)
- 0.7V (lost across the diode) = 0.8V
Using I = V / R = 0.8 / 820 = 1mA
34. Home
1 A power supply drives a current of 500mA through a bulb with a
working resistance of 3W. What voltage is the power supply?
2 A power supply provides 12 V to a bulb passing 3 A. What is the
working resistance of the bulb?
3 A 47 kW resistor has a pd of 9 V across it. What current passes
through the resistor?
4 An 18V power supply is placed across a resistor of resistance
10kW. What current will flow through the resistor?
5 The effective resistance of a small motor is 5 W. What current
passes through it if a cell of voltage 6 V is placed across it?
Solution 1 Solution 2 Solution 3 Solution 4 Solution 5
34
Ohm’s Law - Questions
Return previous slide
35. 35
Ohm’s Law - Solutions
1 A power supply drives a current of 500mA through a bulb with a
working resistance of 3W. What voltage is the power supply?
V = I x R
so V = 0.5 x 3
=1.5 volt
Return
36. 2 A power supply provides 12 V to a bulb passing 3 A. What is the
working resistance of the bulb?
36
Ohm’s Law - Solutions
V = I x R
So R = V / I
= 12 / 3
= 4 A
Return
37. 37
Ohm’s Law - Solutions
3 A 47 kW resistor has a pd of 9 V across it. What current passes
through the resistor?
V = I x R
So I = V / R
= 9 / 47 000
= 0.000 191 A
= 191 mA
Return
38. 38
Ohm’s Law - Solutions
4 An 18V power supply is placed across a resistor of resistance
10kW. What current will flow through the resistor?
V = I x R
so I = V / R
= 18 / 10 000
= 0.001 8 A
= 1.8 mA
Return
39. 5 The effective resistance of a small motor is 5 W. What current
passes through it if a cell of voltage 6 V is placed across it?
39
Ohm’s Law - Solutions
V = I x R
So I = V / R
= 6 / 5
= 1.2 A
Return
40. 40
Power Calculations
The detail from the bottom of an
electrical appliance shown here
gives a very useful, commonly
used method of writing the power
of the appliance.
20 VA is exactly the same as 20 W (20 watts).
The more powerful an appliance is, the greater the number will be.
An electric fire might well be 2 or 3 kW (2 000 or 3 000 W).
1W is sometimes called 1VA because you can calculate the
power by multiplying “the volts by the amps”!
Power = current x voltage or P = I V
Return main menu
41. This device runs from a 230V mains supply. What can we learn from
this information? Well, we know that P = IV; we also know the
voltage and the power, so we can calculate the current I.
41
Power Calculations
Remember that :
20VA means a power of 20W
and that
P = I x V
Return previous slide
I = P / V
So I = 20 / 230
= 87 mA
42. Can you match these typical power ratings with the device that they
describe?
42
Power Calculations
Light emitting diode
Halogen desk lamp
Return previous slide
Power station
Electric lamp
Torch Bulb
43. 43
Power Calculations
Return previous slide
Light emitting diode
Halogen desk lamp
Power station
Electric lamp
Torch Bulb
44. Power Calculations - the formulae
44
Power = current x voltage
P = IV
so I = P / V and V = P / I
But from Ohm’s Law, V = I x R
So P = I x IR
P = I2R
And from Ohm’s Law, I = V / R
So P = (V/R) x V
P = V2/R
Return previous slide
45. Power Calculations - Questions
Home
1 A diode has a voltage of 0.7V across it and a current of 100mA
flowing through it. What is the power dissipated in the diode?
2 A wire carries a current of 5 mA and the power dissipated in the
wire is 2.5 mW. What is the voltage across the wire?
3 What is the current passing through a coil that dissipates 40mW
when a voltage of 5V is applied across it?
4 A current of 10 mA passes through a 10W resistor. What is the
power dissipated in the resistor?
5 A voltage of 9 V is applied across a 10 k W resistor. What power
is dissipated in the resistor?
45
Return previous slide
46. Power Calculations - Solutions
1 A diode has a voltage of 0.7V across it and a current of 100mA
flowing through it. What is the power dissipated in the diode?
46
P = IV
so P = 0.1 x 0.7
= 0.07
= 70 mW
47. Power Calculations - Solutions
2 A wire carries a current of 5 mA and the power dissipated in the
wire is 2.5 mW. What is the voltage across the wire?
47
P = IV
So V = P / I
= 0.000 0025 / 0.005
= 0.000 5 W
= 0.5 mW
= 500 mW
48. Power Calculations - Solutions
3 What is the current passing through a coil that dissipates 40mW
when a voltage of 5V is applied across it?
48
P = IV
So I = P / V
= 0.04 / 5
= 0.008 W
= 8mW
49. Power Calculations - Solutions
4 A current of 10 mA passes through a 10W resistor. What is the
power dissipated in the resistor?
49
P = I2R
= 0.012 x 10
= 0.001
=1mW
50. Power Calculations - Solutions
5 A voltage of 9 V is applied across a 10 k W resistor. What power
is dissipated in the resistor?
50
P =V2/R
= 92 / 10 000
0.0081
= 8.1 mW
51. Resistors in Series and Parallel
Resistors are said to be connected in series when the same current has to
pass through each resistor i.e. the current does not have to split.
These three resistors are connected in series.
51
And so are these 5 resistors
Return to main menu
52. Resistors in Series and Parallel
Resistors are said to be connected in parallel when the current has to
split to pass through each resistor i.e. the current through each resistor
might not be the same.
These three resistors are connected in
52
parallel.
And so are these two.
Return to previous slide
53. Resistors in Series and Parallel
R1 R2 R3
47 MW 47 MW 47 MW
These three resistors connected in series, could be replaced by
one resistor of resistance 141MW.
53
That is 47 MW + 47 MW + 47 MW = 141 MW
(This is not available so we might use a 150 MW)
As a general formula we could write:
R total= R1 + R2 + R3 or R = R1 + R2 + R3
Return to previous slide
54. Resistors in Series and Parallel
54
R1
R2
R3
The resistance of each of the resistors
in this parallel network is 47 MW.
The effective resistance of three
resistors is 15.7 MW (use 16 MW).
You would expect the resistance to be less than any of the individual
resistances in the network as there are three possible routes for the
electricity to take.
The formula used to add the resistances is:
1 = 1 + 1 +
1
R R R R total
1 2 3
or
R R R
1 2 3
RTotal = + +
R R R R R R
1 2 2 3 3 1
Return to previous slide
55. Resistors in Series and Parallel - Questions
1 What is the combined resistance of a 39k W and a 47k W resistor
connected in series?
2 What is the combined resistance of a 39k W and a 47k W resistor
connected in parallel?
3 What is the combined resistance of a 10k W, 20k W and 47k W
resistor connected in series?
4 What is the combined resistance of a 10k W, 20k W and 47k W
resistor connected in parallel?
5 Suppose you need a 30k W resistor but you only have a 27k W
and a handful of assorted resistors. What other resistor would you search
for and how would you connect them together?
55
Home
Return to previous slide
56. Resistors in Series and Parallel - Answers
1 What is the combined resistance of a 39k W and a 47k W resistor
connected in series?
R total= R1 + R2 + R3 or R = R1 + R2 + R3
56
So R = 39 000 + 47 000 = 86 000
= 86kW
Return to menu slide
57. Resistors in Series and Parallel - Answers
2 What is the combined resistance of a 39k W and a 47k W resistor
connected in parallel?
1 1 1
R R R Total
1 2
57
So 1/R = (1/39 000) +(1/47 000)
= 0.00002564 + 0.00002128 = 0.00004692
So R = 1/0.00004692 = 21 314W
= 21.3kW
= 22kW
Return to menu slide
= +
58. Resistors in Series and Parallel - Answers
3 What is the combined resistance of a 10 kW, 20 kW and 47 kW
resistor connected in series?
R total= R1 + R2 + R3 or R = R1 + R2 + R3
58
So R = 10 000 + 20 000 + 47 000
= 77 000 W
= 77 k W
Return to menu slide
59. Resistors in Series and Parallel - Answers
4 What is the combined resistance of a 10kW, 20kW and 47kW
resistor connected in parallel?
1 = 1 + 1 +
1
R R R R Total
1 2 3
The numbers here could get very big so let us omit three zeros and give
the answer in kW as all the resistances are in kW anyway.
59
R = (1/10) +(1/20) +(1/47)
= 0.1000 + 0.0500 + 0.0213 = 0.1713
=5.84 kW
Use 5.8 kW
Return to menu slide
60. Resistors in Series and Parallel - Answers
5 Suppose you need a 30 kW resistor but you only have a 27 kW
and a handful of assorted resistors. What other resistor would you search
for and how would you connect them together?
You are looking to increase the resistance by adding another resistor.
This can only be done by adding a resistor in series.
R total= R1 + R2 + R3 or R = R1 + R2 + R3
60
We know that Rtotal is 30 kW and R1 is 27 kW
So 30 = 27 + R2
R2 = 30 - 27
= 3 kW
Return to menu slide
61. Capacitors
Capacitors store charge. The greater the
voltage that you apply to them, the greater the
charge that they store. In fact the ratio of the
charge stored to the voltage applied is called
the capacitance.
Capacitance = Charge / Voltage
61
or C = Q / V
Capacitance is measured in farad (F) but the farad is a large unit of
capacitance so you usually see microfarad mF (millionth of a farad 10-6
or 0. 000 001 F), nanofarad nF (10-9) or picofarad pF (10-12).
The capacitor in the picture is a 470 mF (0.000 47 F) polar (you must
connect it the correct way around in the circuit) capacitor rated at 40V
(the working voltage should not exceed 40V).
Return to main menu
62. 62
Capacitors - Symbols
This is a non-polar capacitor -
it does not matter which way
around you place it in the
circuit.
This is a polar capacitor. It
is essential that the
capacitor is connected into
the circuit the correct way
around.
Return to previous slide
63. 63
Capacitors
Capacitor Characteristics
Time Constant Calculations
Capacitors in Series
Capacitors in Parallel
Questions
Return to previous slide
64. 64
Capacitor Characteristics
Closing the switch allows the capacitor
to charge. As this happens, the voltage
across the capacitor will rise in line
with the fall of current through it as it
becomes fully charged.
V
A
Voltage
Current
Time
Time
Return to menu slide
65. 65
Capacitor Characteristics
The circuit has now been adapted so
that closing the switch allows the
capacitor to discharge through the
resistor. Note now that the current will
fall as the voltage falls.
V
A
Voltage
Current
Time
Time
Return to previous slide
66. 66
Capacitor Characteristics
The circuit on the left allows us to
investigate the charging and discharging
of a capacitor simply.
Connecting the flying lead S to point X
will charge the capacitor from the cell
through the resistor R.
Connecting the flying lead S to Y will
then discharge the capacitor through the
resistor.
S
It has been found that increasing either the capacitance or the
resistance will increase the time taken for the capacitor to charge.
Return to previous slide
A
V
X Y
C
R
67. 67
Capacitor Characteristics
When the flying lead S is connected to X,
the capacitor will charge up through the
resistor.
At first there will be little or no charge in the
capacitor so the current flows into the
capacitor (via the resistor), quite rapidly.
The current through the resistor develops a
voltage over the resistor. The voltage across
the capacitor will be proportional to the
charge in it. Since the charging has only just
begun, it will be small but growing.
S
The capacitor begins to charge: It gets harder for more charge to flow
into the capacitor so the current decreases. As the charge on the
capacitor is increasing, the voltage across it increases too.
Return to previous slide
A
V
X Y
C
R
68. Home
The capacitor is said to be fully charged..
68
A
V
Capacitor Characteristics
X Y
C
S
R
Eventually the capacitor will “fill”. This
really means that it approaches the condition
such that the voltage across it is equal to the
supply voltage.
There will no longer be any current flowing.
The time taken to achieve this increases with
increased capacitance and /or resistance.
Increasing the supply voltage makes no difference to the time taken
for the voltage across the capacitor to approach the voltage across the
supply.
Return to previous slide
69. Time Constant Calculations
69
The time constant is the time taken for:
the current or voltage to have fallen to 37% of its original value
or
the voltage to have risen to 63% of its original value
We can calculate the time constant for a circuit by multiplying the
capacitance of the capacitor by the resistance of the resistor:
T = C x R
The units of the time constant are seconds if the resistance is in ohms
and the capacitance in farads.
Return to menu
70. Time Constant Calculations
E.G. One
A 10M0 resistor is connected in series with a 470 pF capacitor. How
long will it take to discharge the capacitor to 37V from an initial voltage
of 100V?
Note that the voltage is falling to 37% of its initial value, so we are
looking at one time constant.
70
Using T = C R
T = 0.000 000 000 470 x 10 000 000
= 0.004 7 s
Return to previous slide
71. Time Constant Calculations
E.G. Two
A 10M0 resistor is connected in series with a capacitor. If the time
constant is 0.001s, what is the capacitance of the capacitor?
71
Using T = C R
0.001 = C x 10 000 000
C = 0.001 / 10 000 000
= 0.000 000 000 1 F
= 100 pF
Home
Return to previous slide
72. 72
Capacitors in Series
C1 C2 C3
These three capacitors are
connected in series. Their combined
capacitance is given by:
1 = 1 + 1 +
1
C C C C total
1 2 3
or
C C C C Total + +
1 2 3
C C C
1 2 3
=
Return to menu
73. Capacitors in Series
Home
4 What is the combined capacitance of a 10 mF, 20 mF and 47 mF
capacitor connected in series?
C C C C Total + +
1 2 3
C C C
The numbers here could get very small so let us omit 5 zeros and give
the answer in mF as all the capacitances are in mF anyway.
73
C = (10 x 20 x 47) / (10 + 20 + 47)
= 9400 / 77
=122 mF
1 2 3
=
C1 C2 C3
Return to previous slide
74. 74
Capacitors in Parallel
C1
C2
C3
These three capacitors are connected in
parallel with each other.
Note that because they are in parallel,
they must have the same voltage
across each other.
The combined capacitance of the network
of capacitances is given by:
Ctotal = C1 + C2 + C3
Return to menu
75. Home
Suppose that the capacitances are 10 mF, 20
mF and 47 mF.
75
Capacitors in Parallel
C1
C2
C3
Ctotal = C1 + C2 + C3
So C = 10 + 20 + 47
= 77 mF
Return to previous slide
76. 76
Capacitors - Questions
1 What is the combined capacitance of a 10pF and a 20pF capacitor
connected in series?
2 What is the combined capacitance of a 10pF and a 20pF capacitor
connected in parallel?
3 What is the time constant for a 1000 pF capacitor connected to a
100kW resistance?
4 What capacitance would you need to combine with a 200 mF
capacitor to give the combinations a capacitance of 100 mF? How would
you connect them together to achieve this?
5 What resistor could you connect with a 47 mF capacitor to give a
time constant of 1.83 s ?
Return to previous slide
77. C C C C Total + +
C C C
77
Capacitors - Answers
1 What is the combined capacitance of a 10pF and a 20pF capacitor
connected in series?
1 2 3
The numbers here could get very small so let us omit 11 zeros and give
the answer in pF as all the capacitances are in pF anyway.
C = (10 x 20) / (10 + 20)
= 200 / 30
=6.7 pF
1 2 3
=
C1 C2 C3
Return to menu
78. 78
Capacitors - Answers
2 What is the combined capacitance of a 10pF and a 20pF capacitor
connected in parallel?
C1
C2
C3
Ctotal = C1 + C2 + C3
So C = 10 + 20
= 30 pF
Return to menu
79. 79
Capacitors - Answers
3 What is the time constant for a 1000 pF capacitor connected to a
100kW resistance?
T = C x R
= (1000 x 0.000 000 000 001) x 100 000
= 0.000 1 s
Return to menu
80. C C C C Total + +
C C C
80
Capacitors - Answers
4 What capacitance would you need to combine with a 200 mF
capacitor to give the combinations a capacitance of 100 mF? How would
you connect them together to achieve this?
In order to get a smaller capacitance, you need to connect them in series.
1 2 3
1 2 3
=
C1 C2 C3
So 100 = 200 x C2 / (200 + C2)
100 (200 + C2) = 200C2
20 000 + 100C2 = 200C2
20 000 = 200C2 - 100C2
100 C2 = 20 000
C2 = 200 mF Return to menu
81. 81
Capacitors - Answers
5 What resistor could you connect with a 47 mF capacitor to give a
time constant of 1.83 s ?
T = C x R
1.83 = 0.000 047 x R
R = 1.83 / 0.000 047
= 38 936 W
Use 39 kW
Return to menu
82. 82
Alternating Current
Direct current (DC) is the current that comes from a cell or battery.
It is unidirectional. That is to say that the net drift of electrons is in one
direction. This one direction will always be from positive to negative for
electrons but negative to positive for conventional flow.
It is easier to convert voltages from one value to another if the direction
of the current is rapidly changing.
This is called an alternating current (AC).
Return to main menu
83. 83
Alternating Current
Alternating current has some strange properties:
•it can appear to pass through a capacitor
•it produces the discharges that you see in a plasma ball
•it can be stepped up (to higher voltages and lower current)
•it can be stepped down (to lower voltages and higher current)
Mains voltage is always due to an alternating current. It is used because
it can be stepped up or down easily.
Return to previous slide
84. 84
Alternating Current
Throughout Europe, mains voltage is supplied at a frequency of 50 Hz.
You will remember that Hz is the abbreviation for hertz - the unit of
frequency.
This means that the electricity goes through one complete cycle 50 times
every second.
This means that the voltage will:
•start from zero and build up in one direction until it reaches a
maximum value (about 325 V).
•Fall back to zero
•Change direction and start to build up to a maximum value (about -
325 V)
•Fall back to zero
•50 times per second
Alternating voltages (and currents) can have extremely high frequencies.
The current that produces radio waves can be many MHz (millions of
hertz). Return to previous slide
85. 85
Alternating Current - Questions
Home
1 What is the frequency of the mains voltage in the UK and
Europe?
2 What is the frequency of the mains voltage in the USA?
3 How long is a complete cycle of mains ac at 50 Hz?
4 How many times does the electricity in 50 Hz ac mains, change
direction?
5 Write out 250 MHz in full.
Return to previous slide
86. Alternating Current - Answers
1 What is the frequency of the mains voltage in the UK and
Europe? 50Hz
2 What is the frequency of the mains voltage in the USA? 60Hz
3 How long is a complete cycle of mains ac at 50 Hz?
86
1/50th of a second = 0.02s
Home
4 How many times does the electricity in 50 Hz ac mains, change
direction?
Twice each cycle so 100 times
5 Write out 250 MHz in full
250 000 000 hertz
Return to menu
87. 87
Waveforms
As alternating currents and voltages vary with time, it is useful to have a
graphical representation of them.
The electronic device that does this for us is called an oscilloscope.
The essence of an oscilloscope is its ability to plot a graph for us,
showing the variation of voltage with time. It is particularly useful
because it works extremely quickly and it barely interferes with the
circuit from which you are taking the measurements.
When you first look at an oscilloscope, the number of knobs, levers and
buttons can be bewildering but you will soon get used to it. In fact, you
rarely need to use most of them.
Return to menu
88. 88
Waveforms
Screen showing the trace On / off switch
x input
The trace shows a graph with voltage on the y axis (vertical) and time on
the x axis (horizontal).
Return to previous slide
89. 89
Waveforms
The waveform produced by mains voltage looks like this:
Voltage
time
This shape of waveform is called a sinusoidal wave.
Return to previous slide
90. 90
Waveforms
The waveform produced by mains voltage looks like this:
Voltage
time
The arrows indicate a complete cycle. A cycle is the time that it takes to
reach the next adjacent identical position on the waveform.
Return to previous slide
91. Waveforms
The waveform produced by mains voltage looks like this:
91
Voltage
time
This arrow indicates the peak voltage. For mains it is about 325V in the
UK. The value of 230V that is quoted is the peak divided by the square
root of 2. (It is the dc equivalent voltage that would produce the same
heating effect as an ac with a peak voltage of 325V. Dividing by root 2
only works for sinusoidal waveforms). The peak voltage is the maximum
voltage.
Return to previous slide
92. Waveforms
The waveform produced by mains voltage looks like this:
92
Voltage
time
This arrow indicates the peak to peak voltage. Notice that the peak to
peak voltage is twice the peak voltage. For mains it is about 650V in the
UK and Europe.
Return to previous slide
93. 93
Waveforms
Another common waveform called the square wave looks like this:
Voltage
time
The arrows indicate a complete cycle. A cycle is the time that it takes to
reach the next adjacent identical position on the waveform.
Return to previous slide
94. 94
Waveforms
Another common waveform called the square wave looks like this:
Voltage
time
This arrow indicates the peak voltage.
Return to previous slide
95. 95
Waveforms
Another common waveform called the square wave looks like this:
Voltage
time
This arrow indicates the peak to peak voltage. It will be twice the peak
voltage
Return to previous slide
96. 96
Waveforms
Another common waveform called the saw-tooth wave looks like this:
Voltage
time
The arrows indicate a complete cycle. A cycle is the time that it takes to
reach the next adjacent identical position on the waveform.
Return to previous slide
97. 97
Waveforms
Another common waveform called the saw-tooth wave looks like this:
Voltage
time
This arrow indicates the peak voltage.
Return to previous slide
98. 98
Waveforms
Another common waveform called the saw-tooth wave looks like this:
Voltage
time
This arrow indicates the peak to peak voltage.
Return to previous slide
99. 99
Waveforms - Questions
Home
1 What is the name of the
trace shown on the oscilloscope?
2 How many complete cycles
can you see?
3 If the scale on the y-axis is 2V per division, estimate the peak
voltage. What is the peak to peak voltage?
4 If the scale on the x-axis is 2ms per division, estimate the
length of a cycle.
5 Using your answer to question 4, calculate the frequency of
the wave.
Return to previous slide
100. 100
Waveforms - Answers
1 What is the name of the
trace shown on the oscilloscope?
Return to menu
101. 101
Waveforms - Answers
2 How many complete cycles
can you see?
ONE TWO THREE
Return to menu
102. 3 If the scale on the y-axis is
2V per division, estimate the peak
voltage. What is the peak to peak
voltage?
102
Waveforms - Answers
5 divisions
so 5 divisions x 2 V per division
= 10V
Return to menu
103. 103
Waveforms - Answers
4 If the scale on the x-axis is
2ms per division, estimate the length
of a cycle.
Count as many complete cycles as you can to get as accurate an
answer as possible.
3 cycles is about 35 divisions
1 cycle is about 11.7 divisions
11.7 divisions is 11.7 x 2 ms
= 23.4 ms
Return to menu
104. 104
Waveforms - Answers
5 Using your answer to question 4, calculate the frequency of the
wave.
From question 4 one cycle is about = 23.4 ms
23.4ms = 23.4 x 0.001s
= 0.0234s
How many of these can we get into 1 second?
= 1 / 0.0234
= 42.7 Hz
Return to menu
105. 105
The Potential Divider
Voltage is sometimes referred to as
potential difference. The potential divider
simply divides up a potential or voltage.
In its simplest form it is two resistors
placed across a power supply. The voltage
across of each resistor is less than the
supply voltage. Adding the voltage across
each resistor will give the supply voltage.
It is probably easiest to understand if you
look at the diagram.
+9V
0 V
Here the power supply is 9V. Note that both
the resistances are the same.
The voltage from the supply will be split (divided) equally as 4.5V. Of
course 4.5V + 4.5V = 9V.
Return to menu
106. 106
+9V
0 V
The Potential Divider
In this potential divider circuit, the
resistances are not the same.
2 000 W 1 000 W
The bigger resistance here
means that there will be a
bigger voltage here.
The smaller resistance here
means that there will be a
smaller voltage here.
It is 2/3rds
of the
resistance.
It is 2/3rds
of the
resistance.
It is 1/3rd
of the
resistance.
It is 1/3rd
of the
resistance.
It develops
2/3rds of
the
voltage.
It develops
2/3rds of
the
voltage.
It develops
1/3rd of
the
voltage.
It develops
1/3rd of
the
voltage.
2/3 x 9V = 6V
1/3 x 9V = 3V
If you would like to work through this again, step back through
the sequence using the left arrow key.
Return to previous slide
107. 107
+V
0 V
The Potential Divider
R1
R2
V1
V2
You can calculate the voltage across each
resistor using a formula too.
VV11 VV 11 == VV xx RR11 // ((RR11 ++ RR22))
V1 = 9 x 2 000 / (1 000 + 2000) = 9 x 2 / 3 = 6V
VV 22 == VV xx RR22 // ((RR11 ++ RR22))
V1 = 9 x 1 000 / (1 000 + 2000) = 9 x 1 / 3 = 3V
Return to previous slide
108. 108
The Potential Divider
The potential divider does not have to be made up of two fixed resistors.
One of them could be variable, or even both.
R1
R2
V1
V2
As R1 increases so does V1 but V2
will fall.
As R1 decreases so does V1 but V2
will rise.
It is just as if there is only one cake to
go around (the voltage). If R1
increases then V1gets more cake so
there is less left for V2!
Return to previous slide
109. 109
The Potential Divider
Now the variable resistor has been moved to the lower position in the
network..
R1
R2
V1
V2
As R2 increases so does V2 but V1
will fall.
As R2 decreases so does V2 but V1
will rise.
It can be handy to change the position
of the variable resistor. Later you will
see that it can change the action of a
transistor circuit so make sure that
you follow it.
Return to previous slide
110. 110
The Potential Divider
+V
0V
With this potential divider, the “tap” in the
middle is a “slider”. It probably moves
along a track of carbon.
R1 and V1 will be the resistance and
voltage “above” the slider.
R1 V1
R2 and V2 will be the resistance and
voltage “below” the slider.
R2 V2
As R1 increases, R2 decreases. This will
result in V1 increasing and V2 decreasing.
As R1 decreases, R2 increases. This will
result in V1 decreasing and V2 increasing.
Return to previous slide
111. Here is a component that could be used as a potential divider.
The black ring is
the carbon track.
You adjust it by
putting a
screwdriver in
here and turning
the outer metal
ring.
111
The Potential Divider
Return to previous slide
112. You adjust it by
putting a
screwdriver in
here and turning
the outer metal
ring.
112
The Potential Divider
Return to previous slide
Here is another:
113. It is possible to use many different components that vary their resistance
in a potential divider circuit. Here are a few that you might find and the
physical conditions that change their resistance.
Light Dependent Resistor (LDR) - decreases resistance with increased
illumination.
Thermistor - decreases its resistance with increased temperature
(negative temperature coefficient).
Microphone - changes resistance with sound.
Strain gauge - changes its resistance when stressed.
Photodiode - decreases resistance with increased illumination.
113
The Potential Divider
Return to previous slide
114. The Potential Divider - Questions
1 A 2k and a 3k resistor are used in potential divider using a 10V
supply. Sketch a possible set up and label the resistors and the voltages
across them.
2 Suggest two possible fixed resistors that could be used to obtain
3V from a 15V supply.
3 A 27k and a 62k resistor are used in potential divider using a
12V supply. Sketch a possible set up and label the resistors and the
voltages across them.
4 A 15V supply is attached across a potential divider. If one of the
resistors is a 390k and there is a voltage of 9V across the other, what is
the second resistance?
5 A potential divider is created from a fixed resistor and an LDR.
Explain how the network produces different voltages.
114
Home
Return to previous slide
Answer
Answer
Answer
Answer
Answer
115. The Potential Divider - Answers
1 A 2k and a 3k resistor are used in potential divider using a 10V
supply. Sketch a possible set up and label the resistors and the voltages
across them.
115
+10V
0 V R 1 = 2 000 W
V1= 4V
V2 = 6V
VV11 VV 11 == VV xx RR11 // ((RR11 ++ RR22))
V1 = 10 x 2 000 / (3 000 + 2000) = 10 x 2 / 5 = 4V
VV 22 == VV xx RR22 // ((RR11 ++ RR22))
V1 = 10 x 3 000 / (3 000 + 2000) = 10 x 3 / 5 = 6V
R 2 = 3 000 W
Return to menu
116. The Potential Divider - Answers
2 Suggest two possible fixed resistors that could be used to obtain
3V from a 15V supply.
VV11 VV 11 == VV xx RR11 // ((RR11 ++ RR22)) So 3 = 15 x R1 / (R1 + R2)
We could use more or less any combination. However, they should be
quite high so that they do not drain a lot of current.
116
Let us choose R1 as being 100k.
3 = 15 x 100 / (100 +R2)
3(100 + R2) = 1 500
300 + 3R2 = 1 500
3R2 = 1 500 - 300 = 1 200
R2 = 1 200 / 3 = 400k.
Return to menu
117. The Potential Divider - Answers
3 A 27k and a 62k resistor are used in potential divider using a
12V supply. Sketch a possible set up and label the resistors and the
voltages across them.
VV11 VV 11 == VV xx RR11 // ((RR11 ++ RR22))
V1 = 12 x 27 / (27 + 62) = 12 x 27 / 89 = 3.64V
VV 22 == VV xx RR22 // ((RR11 ++ RR22))
117
+12V
0 V R 1 = 27kW
V1= 3.64V
V2 = 8.36V
V1 = 12 x 62 / (27 + 62) = 12 x 62 / 89 = 8.36V
R 2 = 62kW
Return to menu
118. The Potential Divider - Answers
4 A 15V supply is attached across a potential divider. If one of the
resistors is a 390k and there is a voltage of 9V across the other, what is
the second resistance?
118
So V1 = 15 - 9 = 6V
VV11 VV 11 == VV xx RR11 // ((RR11 ++ RR22))
Now 6 = 15 x R1 / (R1 +390)
6 (R1 + 390) = 15 R1
6 R1 + 2 340 = 15 R1
9R1 = 2 340
R1 = 2 340 / 9 = 260k so use 270k
Return to menu
119. The Potential Divider - Answers
5 A potential divider is created from a fixed resistor and an LDR.
Explain how the network produces different voltages.
In bright illumination the LDR’s resistance falls. The voltage across the
LDR will consequently fall while the voltage across the fixed resistance
will rise.
As it goes dark, the LDR’s resistance will increase, increasing the
voltage across the LDR. As this happens, the voltage across the resistor
will fall.
119
Return to menu
120. The transistor is a three connection component that can be used either as
an amplifier or a switch.
+V
0V
120
Transistor Circuits
+0.7V
base
collector
emitter
Essentially the circuit is set up so as to try to force electrons through the
emitter and out of the collector. This might be to light a bulb.
However, under normal circumstances, there is a very high resistance
between the emitter and the collector so the bulb will not light.
If we make the base go positive, the collector / emitter junction conducts
and the bulb will light. Return to menu
121. 121
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
The base bias voltage is the voltage between
the base and the emitter. If it is anything
much less that 0.7V, the transistor will be off.
The transistor switches
on when it is 0.7V.
You should never allow the base bias voltage
to get too high as this will overheat the base
and burn out the transistor. For this reason
you will frequently find a resistor connected
to the base.
c
e
b
Rb
Return
122. Correct selection of the
two resistors Rand R1 2
will take the base to
0.7V and turn the
transistor on.
Suppose Rwas much
2 higher than R. The
1voltage across Rwould
2 be high so the transistor
would switch on. 122
Return
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
This can be achieved
using a potential divider.
Rb
R1
R2
123. 123
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
Rb
R1
R2
Now suppose R2 was an
LDR.
In the bright light, its
resistance would be low
so the voltage across it
would be low, the
transistor switched off
and the lamp off.
But suppose that it
now goes dark!
Return
124. It has just gone dark!
The resistance of the
LDR rises.
The voltage across the
LDR rises.
The base bias voltage
reaches 0.7V
The transistor
switches on. The bulb lights. 124
Return
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
Rb
R1
R2
125. 125
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
Rb
R1
R2
Suppose that we now
swap the positions of
the resistor and the
LDR.
The bulb will now come
on in daylight! It might
be useful as a warning
light circuit in certain
circumstances.
Return
126. 126
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
Rb
R1
R2
Now let us consider:
•Ib the base current
that flows into the
transistor
•Ie the emitter
current that flows
out of the transistor
Ib
Ie
•IC the collector
current that flows
into the transistor
Ie = Ib + Ic
Ic
Return
127. 127
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
Rb
R1
R2
Ib
Ie
Ie = Ib + Ic
Ic The base current will
be very small as it has
passed through R1 and
Rb so it is almost true
that Ie = Ic.
The ratio of Ic : Ib is
important. It shows
that the transistor is
amplifying. It is often
around about 100. Return
128. Ie = Ib + Ic
That is to say that the Ic
collector current is a
always a constant
amount bigger than
the base current.
Feed a small current
to the base and you
get a big current in
the collector.
128
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
Rb
R1
R2
Ib
Ie
Return
129. 129
Transistor Circuits
The clever part now is to control the base bias voltage that turns the
transistor on.
+V
0V
c
e
b
Rb
R1
R2
Ib
Ie
Ie = Ib + Ic
Ic The ratio is called hfe.
hfe = Ic / Ib
Return
130. 130
Click on a
component to find
out what it does.
Transistor Circuits
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
131. 131
Transistor Circuits
Click on a
component to find
out what it does.
Capacitor
This stores charge. It
acts as a time delay
to any switching. If
the transistor is on
and tries to go off, it
will act as a reservoir
and keep the
transistor on for a
while longer.
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
132. 132
Click on a
component to find
out what it does.
LDR Light
Dependent Resistor
Its resistance
decreases with
increased
illumination. In the
dark, the resistance
goes up turning the
transistor on.
Transistor Circuits
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
133. 133
Click on a
component to find
out what it does.
Base Bias Resistor
This fixed resistor
protects the base
from too much
current.
Transistor Circuits
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
134. 134
Click on a
component to find
out what it does.
Potential Divider
The LDR and R2 are
a potential divider.
Transistor Circuits
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
135. 135
Click on a
component to find
out what it does.
Transistor
A small voltage at
the base will allow
current to flow
through the emitter
from the collector.
Transistor Circuits
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
136. 136
Click on a
component to find
out what it does.
Diode - this only
allows current to
flow in the direction
of the arrow head.
Rapid changes in the
magnetic field of the
relay can cause high
voltage that would
damage the
transistor.
The diode
diverts the
currents
formed by
this
process.
Transistor Circuits
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
137. 137
Click on a
component to find
out what it does.
Relay - current
through the relay
produces a magnetic
field that throws a
switch in another
external circuit. The
external circuit can
be a much higher
powered circuit.
Transistor Circuits
+V
0V
c
e
b
Rb
R1
R2
C1
Relay
CONTINUE
Return
138. Transistor Circuits - Questions
1 The collector current in a circuit is 120mA when the base current
is 3mA. What is hfe and the emitter current?
2 Why do we connect a resistor directly to the base of the
transistor?
3 Sketch a circuit that will throw a relay in the dark that in turn will
turn on a switch.
4 Why should a diode be connected across a relay in the collector
circuit of a network?
5 Explain what happens when the resistance of the base bias
resistor falls in a transistor circuit controlling a motor.
138
Answers:
1 2 3 4 5
Return to previous slide
139. Transistor Circuits - Answers
1 The collector current in a circuit is 120mA when the base current
is 3mA. What is hfe and the emitter current?
139
hfe = Ic / Ib
= 120 / 3
= 40
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140. Transistor Circuits - Answers
2 Why do we connect a resistor directly to the base of the
transistor?
The resistor limits the current entering the base. This stops the base from
overheating due to excessive currents which would burn the transistor
140
out.
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141. Transistor Circuits - Answers
3 Sketch a circuit that will throw a relay in the dark that in turn will
turn on a switch.
141
+V
0V
c
e
b
R1
C1
Relay
LDR
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142. Transistor Circuits - Answers
4 Why should a diode be connected across a relay in the collector
circuit of a network?
The relay can create large voltages due to rapid changes in magnetic
fields as they switch off. The diode provides a short circuit for the
current due to this voltage. As diodes only carry current in one direction,
the diode connected to the relay will have no effect in normal operation
142
of the relay.
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143. Transistor Circuits - Answers
5 Explain what happens when the resistance of the base bias
resistor falls in a transistor circuit controlling a motor.
As the resistance falls, so will the voltage across it.
The voltage across the base will consequently fall.
143
This will turn off the transistor.
The collector current will fall to zero (or extremely close to zero).
The motor will switch off.
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144. 144
Electronics Questions
1 What is the nominal value and tolerance of this resistor?
2 A power supply drives a current of 150mA through a bulb with a
working resistance of 10W. What voltage is the power supply?
3 What is the current passing through a heater that dissipates 40W
when a voltage of 10V is applied across it?
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145. 4 What is the combined resistance of a 30k W, 20k W and 47k W
resistor connected in parallel?
5 Suppose you need a 50k W resistor but you only have a 47k W
and a handful of assorted resistors. What other resistor would you search
for and how would you connect them together?
6 What is the combined capacitance of a 47pF and a 20pF capacitor
connected in series?
7 What is the combined capacitance of a 47pF and a 20pF capacitor
connected in parallel?
8 What is the time constant for a 1000 mF capacitor connected to a
10MW resistance?
145
Electronics Questions
Return to previous slide
146. 9 If the scale on the y-axis is 4mV per division, estimate the
peak voltage. What is the peak to peak voltage?
10 If the scale on the x-axis is 50 ms per division, estimate the
length of a cycle. Using your answer, calculate the frequency of the
wave.
146
Electronics Questions
Return to previous slide
148. 1 What is the nominal value and tolerance of this resistor?
This gold band indicates that the tolerance
of the resistor is ±5% (plus or minus 5 percent).
The third band is black. This means that there are no zeros.
The second band is green. This means the second digit is 5.
The first band is violet. This means the first digit is 7.
148
So the resistor is nominally 75 W.
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Electronics Answers
149. 2 A power supply drives a current of 150mA through a bulb with a
working resistance of 10W. What voltage is the power supply?
149
V = I x R
so V = 0.15 x 10
=1.5 V
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Electronics Answers
150. 3 What is the current passing through a coil that dissipates 40W
when a voltage of 10V is applied across it?
150
P = IV
So I = P / V
= 40 / 10
= 4 W
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Electronics Answers
151. 4 What is the combined resistance of a 30kW, 20kW and 47kW
resistor connected in parallel?
R R R R Total + +
1 2 3
R R R
1 2 3
151
=
The numbers here could get very big so let us omit three zeros and give
the answer in kW as all the resistances are in kW anyway.
R = (30 x 20 x 47) / (30 + 20 + 47)
= 28 200 / 97
=291 kW
Use 300 kW
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Electronics Answers
152. 5 Suppose you need a 50 kW resistor but you only have a 47 kW
and a handful of assorted resistors. What other resistor would you search
for and how would you connect them together?
You are looking to increase the resistance by adding another resistor.
This can only be done by adding a resistor in series.
R total= R1 + R2 + R3 or R = R1 + R2 + R3
152
We know that Rtotal is 50 kW and R1 is 47 kW
So 50 = 47 + R2
R2 = 50 - 47
= 3 kW
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Electronics Answers
153. 6 What is the combined capacitance of a 47pF and a 20pF capacitor
connected in series?
C C C C Total + +
1 2 3
C C C
The numbers here could get very small so let us omit 11 zeros and give
the answer in pF as all the capacitances are in pF anyway.
153
C = (47 x 20) / (47 + 20)
= 940 / 67
=14 pF
1 2 3
=
C1 C2 C3
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Electronics Answers
154. 7 What is the combined capacitance of a 47pF and a 20pF capacitor
connected in parallel?
154
C1
C2
C3
Ctotal = C1 + C2 + C3
So C = 47 + 20
= 67 pF
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Electronics Answers
155. 8 What is the time constant for a 1000 mF capacitor connected to a
10MW resistance?
155
T = C x R
= (1000 x 0.000 001) x 10 000 000
= 10 000 s
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Electronics Answers
156. 9 If the scale on the y-axis is
4mV per division, estimate the
peak voltage. What is the peak to
peak voltage?
156
5 divisions
so 5 divisions x 4mV per division
= 20mV
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Electronics Answers
157. Electronics Answers
10 If the scale on the x-axis is 50
ms per division, estimate the length of
a cycle.
Count as many complete cycles as you can to get as accurate an answer
as possible.
157
3 cycles is about 35 divisions
1 cycle is about 11.7 divisions
11.7 divisions is 11.7 x 2 ms
= 23.4 ms
158. 10 continued Using your previous answer, calculate the frequency of
the wave.
From question 4 one cycle is about = 23.4 ms
158
23.4 ms = 23.4 x 0.000 001s
= 0.000 023 4s
How many of these can we get into 1 second?
= 1 / 0.000 023 4s
= 42.7 kHz
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Electronics Answers
159. Home
Retu1r5n9 to previous slide
Introduction
Ohm’s Law
Power Calculations
Resistors in Series and Parallel
Capacitors
Alternating Current
Waveforms
Transistor Circuits
The Potential Divider
Components
Questions