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Form 2 Integrated Science – Electricity.PDF

This document contains very informative and detailed notes on Electricity and concepts related to it. It covers flow of electricity to electric terms to safety with electricity to circuit symbols to types of circuits to circuit overload to electricity bills and meters.

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Electricity
Objectives ⬡ Define conductors and insulators ⬡ Classify items as conductors and insulators ⬡ Define the usefulness of conductors and insulators ⬡ Explain safety rules to follow when dealing with electricity and the electrical mains ⬡ Explain the concept of electricity and the terms use in electricity ( charge, current, voltage, resistance and power). ⬡ Identify the symbols of a simple circuit (switch, cell, battery, fuse, bulb and wire). ⬡ Compare series and parallel circuit. ⬡ Discuss the danger of overloading and short circuiting. ⬡ List safety devices used to prevent electrical disasters. ⬡ Read an electrical meter to determine energy usage. ⬡ Calculate the cost of electrical usage 2
Electricity The flow of electrons (or ions)
Electricity is a form of energy. One which is very important in our daily lives for both convenience as well as a necessity. It is however one of the most dangerous forms of energy if not handled properly. Heat energy is a bi-product of electricity. However not all materials can accommodate this form of energy. As a result of this we can categorize all materials as either: conductors or insulators.
Conductors and Insulators Insulators ⬡ these are materials which oppose the flow of electricity. These materials would have high resistance. Conductors ⬡ these are materials which allow the flow of electricity. These materials generally have low resistance. Examples of conductors: Copper, Iron, Stagnant water, Gold Examples of insulators: Rubber, wood, concrete, soil 5
Conductors and insulators are equally important in our daily lives. This is because conductors which do not have insulators covering them would be dangerous as if you were to come into contact with it, you would be shocked. Therefore insulation is needed to prevent exposure to electrical shock. As a result of the danger conductors and electricity possess, safety features have to be taken in order to prevent damage or possible death.
Safety measures taken in dealing with electricity:
Make sure the main switch is off before handling any circuit. ⬡ This is to avoid electrical shock(In handling circuits, whether it is repairing or adjusting parts there is a strong possibility of electrical shock and therefore the flow of current should be stopped to avoid this). 8
Wear insulated/protective clothing. ⬡ Wearing insulated clothing such as rubber gloves, shoes with rubber soles would help to prevent body parts from coming into direct contact with electricity. 9
⬡ Check wires for broken insulation. ∙ (Wires with broken insulation can cause exposure to electrical shock as skin can come into contact with the conductor inside of the wire) ⬡ Ensure that your hands or protective clothing is free of moisture. ⬡ Use child safety outlet caps in the home. 10
Terms used in electricity ⬡ Current – is the flow of electrons through an electric circuit. The size of the current in circuit can be measured using an ammeter. Symbol ofr electric current is I . the unit used is ampere or amp abbreviated to A. ⬡ Voltage – is the energy that drives electrons through the electric circuit. The greater the voltage the larger the numbers of electrons passing through the circuit in one second. Large voltage increase the flow the current through the circuit (the more current that will be passsing through). Symbol for voltage is V ; the unit is volt ( V). Most Caribbean countries has a voltage od 240 V, except for Barbados, Jamaica and Trinidad which has 110 V. ⬡ Electric Power- power relates to appliances and the power of an applicance is the rate at which it can do work or the amount of electrical energy the appliance uses per second. Power has a symbol P; and unit is watts, W. 11
Circuit Symbols ⬡ Electricians when preparing plans on how to wire houses and buildings would need to construct a “map” of sorts to outline how the wires and bulbs and other devices would be positioned. As a result of this a standard set of symbols have been developed to represent different electrical devices in a circuit. ⬡ Page 63-66 (Active Science book 2), draw symbols in your notebooks 12
Types Of Circuits There are two main types of circuits; Parallel circuits and series circuits.
Parallel Vs Series 14 Series Parallel There is only one pathway for the current There is more than one pathway for the current Current flows through one bulb and then the next Current flows to each bulb directly along its own pathway They have the same current flowing in all parts of the circuit The current is divided when it comes to a junction. Can be turned on and off by a single switch Switches can be put to either turn off all the circuit or just part of it With two or more bulbs they have to share the voltage of the battery and as a result the bulbs are dimmer With two or more bulbs, each bulb gets the full voltage of the battery and therefore the bulbs are brighter however the battery dies faster
Series Parallel 15
Circuit Overload ⬡ Circuit overload- this occurs when a circuit is supplied with more current than it is designed to handle. ⬡ Circuit overload is very dangerous as it can result in damage to the parts which make up a circuit. As heat is a bi- product of electricity circuits are designed with sufficient insulation to handle a certain amount of heat produced by a certain amount of current. If the maximum safe amount of current a circuit is designed to handle is exceeded the parts and insulation on the wires can get hotter than should be and an electrical fire would result. 16
How can a circuit be overloaded? ⬡ Bad wiring- damaged or old wires can have broken insulation or weakened insulation and this can result in electrical shock to persons who touch the wires or electrical fire if the wire gets too hot. ⬡ Too many connections- if too many appliances are plugged into one socket, you may be pulling more current from that socket than it can safely supply. 17
Electrical safety devices ⬡ Fuses- contain a thin metal wire which melts if the current exceeds a safe limit which the fuse would be set to. When this thin metal wire melts it would break the circuit/ cut power. ⬡ Circuit Breakers/ trip switches- these do not contain fuse wires. The current passes around an electromagnet. As the current increases the magnetic field becomes more powerful and eventually would pull apart the contacts on a switch breaking the circuit/ cutting power. 18
Fuses and Circuit breakers: 19
Electrical safety devices ⬡ Surge protectors- if there is a surge of electricity due to lightning the surge protector would shut off protecting the devices plugged into it. ⬡ Lightning rods- these would be position at the highest point on buildings that are in areas prone to lightning strikes. The lightning would be attracted to these metal rods and strike them rather than the building. Usually lightning rods would have earth wires which would transmit the electricity into the ground. 20
Surge protectors and Lightening rods: 21
Reading Electrical Meters ⬡ When we use electricity in the home, we have to pay for the energy we use. This energy is the energy given up by electrons when a current flows through a circuit. ⬡ How can we know how much energy each device will use? ⬡ The values such as 40 watts and 60W that are shown on devices are values of electric power. Power is the rate of using electricity. That is: ⬡ Power= energy/time ⬡ The unit of power is called the watt and the symbol= W. Named after Scottish scientist James Watt. ⬡ Energy is measured in joules. One watt means the same or is equal to one joule per second. ⬡ We can calculate the power in a circuit using the equation: ⬡ Power = voltage X current 22
Calculating electricity bills ⬡ Each household is billed (charged) for the amount of electricity used within a particular period. This given as rate per kWh (kWh means kilowatts per hour). ⬡ In some countries an additional charge for the meter rental and a fuel adjustment charge are also added to the customer’s electricity bill. 23
How to calculate charges on an electricity bill 24
Example of an electric bill 25
Types Of Electrical Meters: 26