CURRENT Current is the continuous movement of free electrons through the conductors of a circuit. Ammeter - Measures the flow of electrons in a circuit, which is known as current - connected in series. Symbol of current (I). The (I) unit of measurement of electric current, the ampere, is named after André-Marie Ampère.
VOLTAGE + The ability of a cell to produce current is called voltage. + Voltage is the electrical potential energy. + Is measured in Volts. + Voltmeter Measures the voltage produced by a power supply – always connected in parallel. + Symbol for Volt (V) or
OHM’S LAW & RESISTANCE Resistance - Free electrons move through conductors with some degree of friction. Resistance is measured in Ohm (Ω). Symbol of resistance (R). A Resistor - Slows down the flow of electrons in a circuit.
EQUATIONS Resistance = voltage/current R= V/I Voltage = current x resistance V= I x R Current = voltage/resistance I=V/R Resistance in Serie: When resistors are connected in Series, the effect is to add more resistance to the circuit. E.g. The value of resistors in series: RT(Total) = R1+R2+R3[Resistor Values] *A resistor is a series circuit is called a voltage divider. Resistance in Parallel: When resistors are connected in parallel, the effect is to reduce the resistance in the circuit. E.g. The value of resistors in parallel: 1/Rt = 1/R1 + 1/R2 + 1/R3 *Resistors in a parallel circuit is called a current divider.
Measured in Volts (V). V = I x R V I = V R R = V I A ΩMeasured in Amps (A). Measured in Ohms(Ω).
RESISTOR COLOUR CODESThe First three bands give thevalue of the resistor in ohm(Ω).The fourth band indicates howaccurate the given value is.Resistor value: 2% - RED 5% - GOLD 10% - SILVERE.g.:
RESISTIVE COMPONENTS Variable Resistor Light Dependent Can be used to adjust resistor (LDR) the flow of current in a It’s a component whose circuit. resistance depends upon the amount of light falling on it – it reacts to light. When the LDR in the circuit is covered up, the Thermistor bulb gets dimmer and Is a component whose finally goes out. resistance varies with temperature.
CONTROL ELECTRICS The switch Single pole double It’s the simplest throw switch (SPDT). control unit form in an Double Pole single electrical circuit. The throw switch (DPST). simplest type of switch is the single Double pole single pole single throw throw switch(DPDT). switch (SPST). It has 2 parts: a pole & a contact. Push to Make & Push to break switches:
MORE COMMON TYPE OF SWITCHES:Toggle switch Push SwitchSlide switch Reed SwitchA Rotary Switch
RELAYS The Relay - is a switch turned on and off by an electromagnet. Relay Latch - Fixes a circuit in “On” position. - A latch is like a lock. Relay Buzzer -The relay switches “on” and “off” very rapidly, producing a buzzing sound. -A relay can therefore be used to make a crude buzzer.
CONTROL ELECTRONICSTHE DIODE LIGHT EMITTING DIODES (LED) Is a semiconductor device. A LED is a special form of diode It’s a component which allows that gives out light when current to flow in one direction connected the correct way only. around. A Semiconductor diode consists LED’s normally need to be of a PN junction and has two connected in series with a terminals: resistor to prevent them drawing [P] - Anode(+) too much current and burning [N] – Cathode(-) out. Current flows from the anode to LED’s are used mainly as visual the cathode within the diode. indicators that a circuit is working When a forward voltage is applied, the diode conducts. or an appliance is “On”. When a reverse voltage is An LED converts electrical applied, their is no conduction. energy to light.
TRANSISTORS A Transistor is a semiconductor device. Made of three layers of N-Type & P-Type semiconductor material, Geranium and Silicone. The three layers are called - Emitter, Base & Collector. There are three types of transistors: NPN PNP The NPN Transistor has a small current flowing to the base of the transistor enables a large current to flow between the collector and emitter. The PNP Transistor uses a small base current and negative base voltage to control a much larger emitter-collector current. The FET transistor – Field Effect Transistor only needs a small field of current.
TIMING CIRCUITSCAPACITORS - A CAPACITOR IS A COMPONENT WHICH CAN STORE AND RELEASE ELECTRICAL ENERGY. - CAPACITANCE IS MEASURED IN FARAD. 1. POLARIZED - CAPACITOR 2. NON – POLARIZED CAPACITOR Polarized capacitors tend to Non-polarized capacitors be higher value types. which are low value types. These have a positive(+) These can be connected and negative(-) lead which either way round in a must be connected the circuit. correct way round in a Do not have a (+) or (-) circuit (+ to + and - to -) . lead. Normally used to smooth a current in a circuit.
THREE FACTORS THAT INFLUENCE THE CAPACITYOF A CAPACITOR: 1.) Lowering the surface area of plates. 2.) Increase distance between plates. 3.)The kind of material used for dielectric.
REFERENCES: Download.pptx. (n.d.). Retrieved from http://www.tes.co.uk/Download.aspx?storycode=6071059&type=X&id=6269844 explaining how Resistors work.ppt. (n.d.). Retrieved from http://teachersunderground.co.uk/Electronics/explaining%20how%20Resistors% 20work.ppt Garratt,J. (1996). Design and Technology. Cape Town: Cambridge University Press. Ohm’s Law - Resources - TES. (n.d.). Retrieved April 30, 2012, from http://www.tes.co.uk/teaching-resource/Ohm-s-Law- 6071059/addtofavourite/addtofavourite/ Resistor colour code wheel.ppt. (n.d.). Retrieved from http://teachersunderground.co.uk/Electronics/Resistor%20colour%20code%20w heel.ppt
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