science electricity

7/28/2019 Science Electricity

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A. Importance of Electricity

We use electricity almost every minute, from the time we get up in themorning until we go to bed at night. We use it in our homes, businesses

and schools. It is an important source of energy as everything aroundus needs it to function. Examples include electrical appliances like thetelevision, computer, refrigerator, electric fan, air conditioner, andrice cooker. Petrol stations cannot pump petrol without it. Businesses

have to close because their cash registers would not work without it.Restaurants cannot cook food without it. In short, our lives almostcome to a standstill without electricity.


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3. The two main sources of electricity are power stations and batteries.Most of the electricity that we get in our homes and offices is generatedby power stations. The flow of electric power is as shown:

4. For us to obtain electricity, al l we need to do is just to plug anelectrical appliance into the electric power point on the wall and turnthe switch on. For lighting in rooms, the flick of the switch that isconnected to electric cables will give us the needed electricity.


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I 5. Batteries come in different shapes and sizes, and some give greater

amounts of electricity than others.

7. Electricity can also be generated through other means.

throughSun light energy ________ ----> electrical energy

the use ofsolar cells


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8. The electricity that powers our home appliances and other devices

come from many different types of power plants, mostly from coalplants, natural gas plants, and nuclear facilities. Other ways to generateelectricity are shown in the diagrams below:

Instead of using coal, some power plants use other ways to make

electricity.


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C. Electric Circuits

9. A battery has two poles: positive pole ( + ) and negative

pole ( ).

10. A bulb wil l l ight up whenit is properly connectedby wires to the positiveand negative poles of a

battery. The bulb lightsup because e lec t r i c i t yflows through the bulb.

11. The wire, the battery and the bulb form an electric circuit. An electric

circuit is a path that allows electricity to flow. It is made up of a power

source (battery) and circuit components (wires, switches and bulbs).

12. In a closed circuit, the electric circuit is complete and electricity can

flow through smoothly.


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14. Electricity usually flows through wires in an electric circuit. The wiresare usually made of copper and other materials that can conductelectricity easily.

15. Abulb lights up when electricity flows through the circuit. The partsof a bulb are summarised as follows:

16. The switch controls the flow of the electric current in a circuit; it joinsor breaks the connection.


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D. Circuit Diagrams

17. A circuit diagram represents an actual circuit. Different componentsof a circuit are represented by different symbols.

18. A circuit diagram is useful when testing a circuit and for understandinghow it works.

19. Tips for drawing a c i rcu i t d iagram: Make sure you use the correct symbol for each component. Draw connecting wires as straight lines (use a ruler). Put a dot () at each junction between wires.

Make sure your drawing is clear and tidy.

An example of a good and bad circuit diagram is shown below:


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20. Here are some examples of circuit diagrams.

( a ) One ba t t e r y w i t h one bu l b and a sw i t ch

( b ) Two ba t t e r i e s w i t h two bu l b s and a sw i t ch


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Arrangement of batter ies If there is only one battery in a circuit, the arrangement of the

battery does not affect the brightness of the bulb.

If two or more batteries are used in a circuit, they can be arranged

in two ways: series and parallel.

In a series, the positive pole of one battery is connected to thenegative pole of the other battery, either directly or by means

of a wire.

In a parallel arrangement, the batteries are arranged such that

each battery is connected to the bulb by a separate path fromthe others.


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Numberof bulbsWhen bulbs are arranged in series, their brig htness decreases

when the number of bulbs increases.

When bulbs are arranged in a parallel arrangement, the brightness

of each bulb is the same.

In a series arrangement, there is only one path for electric current toflow. If one bulb is removed from the connection, the other will


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In a para l l e l a r rangement ,

there is more than one path

for electric current to flow and

each path is connected to onebulb independently. If one bulb

is removed, the other bulb will

continue to light up.

The circuits in our homes and

schools are arranged in parallel.

This means that if any bulb is

damaged or removed, i t wi l l

not affect the remaining bulbs. Switching on or off a fan wouldnot affect the other electrical appliances.


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26. Many metals are good conductors of electricity and heat. Thus,

materials that are good conductors of electricity are generally good

conductors of heat.


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G.Using Electrical Appliances Safely

27. Electric currents can cause fatalities. Here are some safety rules whenusing e lectricity.

Always switch off al l electr ical appliances afte r use.

Do not put foreign objects into electr ic power points.

Do not touch electrical appliances or switches when hands are wet.

Water is a conductor of electricity.

Do not repair electrical appliances on your own. Get a qualified

electrician. Do not carry out experiments involving electricity on your own.

Ensu r e t ha t t he r e a r e no e xposed w i r e s i n an e l e c t r i c a l

equipment.

Do not over load a socket wi th too many p lugs.

Use safety devices such as circuit breakers and fuses to break a circuitwhen there is too much current flowing through the circuit.


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H.Conserving Electricity

28. Conserving electricity does not mean depriving ourselves of comforts

and conveniences. Conservation simply means to guard against waste,

to be aware of the inefficient ways electricity can be used, and to do

something about it.

29. In Singapore, we are dependent on imported fuel to meet our energyneeds. The cost of fuel accounts for about half the total cost ofelectricity. While we cannot control the cost of fuel, we can control

the way we use energy.

30. Saving energy is always a good habit: not only do you save money,but you also save the environment by causing less fuel to be burnt.So plan wisely how you spend energy as you do with your money.


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Choose an appropriate sized refrigerator for your family. Adjust thethermostat to a recommended setting. Check the seals and hinges

for air leakage.

Cook food in a pot with the lid covered. Thaw frozen food in the open rather than using a microwave

oven.

Switch on the water heater just before you shower and switch itoff immediately after you have finished showering.

Dry your clothes under the Sun instead of a dryer. Configure the computers to auto-shutdown after nightly

backups.


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