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The list below gives the various stages of the summary, but they are in the wrong order.

 

Match the stages with the seven sentences of your summary.

Observation Apparatus

Procedure Conclusion

Observation Procedure

 

Purpose of the experiments:

b) Look carefully at the stages of the summary and answer these questions:

1. Could the structure be applied to any experiment?

2. Which parts could be left out, depending on the experiments?

3. Could the order be changed?

 

c) Name the stages in the magnetism experiment in Step 6.

 

Step 8.

Read this description of one of Faradays experiments and make a summary of it. Use the structure you practiced in Step 7

 

Oersteds experiments did not have any immediate practical application. All he had done, in effect, was to show that a wire carrying an electrical current acts like a magnet. The thing that most interested scientists was the question of whether the opposite was true, could magnets be used to induce an

electric current?

Michael Faraday an English scientist carried out a series of experiments to find the answer to this question. His work led to the development of the electric generator and so made it possible to produce electricity on a large scale.

In one of his experiments, Faraday connected a coil to a simple ammeter. Then he took a bar magnet and moved it quickly towards the coil. The ammeter showed a momentary current. When the magnet was moved quickly away from the coil, the ammeter again registered a current but in the opposite direction.

Faradays experiments were only the first steps, but he had shown quite clearly that magnets could be used to produce an electric current. The next step was to show that a momentary movement should induce a continuous current. This is the principle on which all electric generators (and motors) are based

 

LESSON 3

STUDY SECTION

 

Copper is a good conductor of electricity. If a copper wire is connected to a battery, an electric flows in the wire. However a current does not flow if you connect a piece of plastic to the battery. Because plastic is an insulating material, it resists the flow of electricity. Bad conductors of electricity have a high resistance.

 

Look at this diagram. It shows an electric circuit:

battery

wire

lamp gap.

 

Place a piece of copper wire across the gap. The lamp lights. Current flows around

the circuit. After removing the copper, place a piece of nichrome across the gap. The

lamp is dimmer. Nichrome has a high resistance and the current does not flow easily.

This fire uses electricity for heating. The heating element is made of nichrome, which

is a bad conductor of electricity. It has a high resistance and current cannot flow

easily. Therefore, the current passing through the element generates heat.

 

Step 1.

Are these statements true or false? Correct the false ones.

1. An insulator is made of a material, which resists the flow of electricity.

2. An electric current flows easily through a good conductor.

3. If a copper wire is connected to a battery an electric current flows.

4. Nichrome is a good conductor of electricity.

5. If you pass an electric current through nichrome, heat is generated.

6. Rubber has a low resistance to electric current.

7. An electric current flows easily through a material that has a high resistance.

8. The lamp is dimmer when a smaller current flows.

 

Step 2

 

V Voltmetter.

S Switch A Ammeter

Make statements about symbols.

For example:

This is the symbol used for a lamp in an electric circuit diagram A V

(An ammeter is used for measuring electric current. A voltmeter is used for measuring electric energy). Now look at the circuit diagram and read this: The battery is in the middle of the diagram at the top and a voltmeter is connected across it. The lamp is on the left, towards the top, the ammeter is on the right, towards the bottom. The switch is positioned at the bottom and on the left. Now read this and draw the circuit diagram, which is described. The battery is in the middle of the diagram at the bottom and a voltmeter is connected across it. On the right of the diagram is a lamp, which is positioned towards the top. The ammeter is on the left and in the middle and the switch is at the top on the right.

 

Step 3.

Look at this circuit diagram and complete the description V A

The battery ........ in the ........ of the ........ at the ........ and a ... it.

The ....... is in ....... .on ...... right. The lamp is on ........ towards . . . . switch .........

 

Language Point

Resistance is measured in ohms (W)

Current (I) is measured in amps (A)

Voltage (V) is measured in volts (V)

This formula is used to calculate the resistance in a circuit.

V=IR (V equals I times R.)

 

Fill in the gaps:

V- voltage measured in volts,

I-

R-

Look at this circuit diagram: R is the symbol for a resistor. A resistor is made of a material, which resists the flow of electricity. Some resistors are made of nichrome.

To calculate the voltage, V:

V=IR=53t!2=l

V=10 volts

Read out the calculations in full, for example, voltage equals current times resistance, which is five times two.

Now calculate the current, voltage and resistance in the following circuits:

Calculate I Calculate V Calculate R

 

Step 4

Put in the right words. The first one has been done for you.

1. If you connect a copper wire to a battery a current flows.

2. After ... the copper, place a piece of nichrome across the

3. An insulator ... the flow of electricity.

4. An ... is used for ... current.

5. ... is measured in ohms.

6. A voltmeter is connected ... a battery.

7. The switch is ... the top ... the right.

8. Draw a ... diagram that has a battery on the right.

9. Heat is ... when you pass an electric current ... nichrome.

10. To calculate the voltage use this ... .

 

Step 5.

1. If the torch uses 0.5A, the calculator 0.05A, the cassette player 2A, calculate the resistances.

2. On the back of most electrical devices there is the power rating

SONNY JAPAN

MODEL 36

SERIAL 0169423/005

6W 6V

Use this formula for calculating the power of an electrical device

R=IV

Power, P, is measured in watts (W). The power rating of the device is 6W.

Calculate the current that is used

P=IV 6=16 6/6=1 I=1A

 

Look at this table. Fill in the gaps:

electrical device:

power (W)

voltage (V)

current (I)

Electric fire light bulb electric drill

2400 W 55 W 990W

240 V 110V 110V

electric kettle; car headlight; television;

---- 48W 20W

240V 12V 110V

10A ---- ---

Now make statements like this example.

The electric drill has a power rating of 990W. When it is connected to a main supply of 110 volts it uses a current of 9A.

 

 

Step 6.

Fuses usually have four different ratings: , 5A, 10A, I3A.

Make statements about the electrical devices in Step 5 like this example. Use a I3A fuse with an electrical kettle because it draws a current of 10A.

 

Step 7

1. Calculate the resistance of the electrical devices in Step 5.

2. Find out the power rating of other electrical devices, for example, an electric cooker, washing machine, radio, etc.

Language Point

240V - two hundred and forty volts 50A - fifty amps.

LESSON 4

 

Fuses

Starter: Any electrical circuit usually has one or more fuses in it. Why? What would happen if there were no fuses?

Input: Safety with Fuses.

If an appliance such as a light or a heater stops working, it is probably because the fuse has blown. There are 3 main types of fuse in use today - cartridge, rewirable and the most modern type, miniature circuit breakers. Some appliances have their own fuses (usually in the plug), so this should be checked first. Otherwise, check whether the main fuse has gone. The main fuses are normally in a switch box or fuse box at the point where the main electricity supply cable enters the building usually near the front door. Before checking these fuses, turn off the main switch. Remove and examine the fuses one by one. Which the cartridge fuses the simplest thing to do is to take out the old fuse and try a substitute fuse of the correct amp rating, of course.

Then test the appliance, with reliable fuses look for wire breaks or scorch marks on

the fuse carriers. Remove the old wire, fit new wire round the retaining screws and

tighten the screws. Replace the fuse carrier and see if the appliance works. If a fuse

continues to blow, do not fit another fuse, but get an electrician to check the

appliance and the circuit for possible faults. Never attempt to use a fuse of a higher

rating.

Gathering Information

 

Step 1.

From Input, find answers to these questions :

What does a fuse do?

What are the three types of circuit protection?

Where are fuses located in a circuit?

How should you check a cartridge fuse?

What tells you whether a reliable fuse has blown?

What is the first thing to do when checking a main fuse?

What should you do if a new fuse blows immediately?

 

Step 2.

Replace the words and expressions in bold type with ones of similar meaning from the Input.

a) When a rewirable fuse blows, it burns the carrier.

b) Always switch off, before examining the main fuses.

c) When you have put the fuse back, try the appliance again.

d) There is probably something wrong with the circuit, if the fuse blows again.

e) With a reliable fuse you must take out the old wire, then put new wire round the screws and do up the sewers.

 

Step 3

a) What are the advantages and disadvantages of the different types of fuses mentioned?

b) Why shouldnt you fit a fuse of a higher rating?

 

Step 4.

Warnings

Do:

Always turn off the main switch

Always fit a fuse of the correct rating.

 

Dont:

Dont fit a fuse of

Do not do a higher rating.

 

Make warnings from these cues:

a. Check the amp rating of an appliance

b. Handle electricity with wet hands

c. Repair appliances with the power on

d. Use insulated pliers

e. Put too many plugs to one outlet

f. Use old cables or flexes

g. Have a supply of fuse wire available

h. Join wires carelessly.

Step 5.

Conditions and Instructions

 

Look at these examples:

If an appliance stops working, check the fuse.

If a fuse continues to blow, do not fit another fuse.

Choose a condition from A and an instruction from B to make sentences like those in the examples :

A An appliance stops working. You do not know where the fuse box is. You havent got the correct amp fuse. You need to check the main fuse. You know little about electricity. One of the circuit breakers is switched off. Check whether one of the switches is off. Look near the front door. Check the appliance fuse first. Use a higher amp rating. Check the circuit or appliance. Try to fit electrical faults yourself. Switch the circuit on again. B The appliance has got its own fuse. The fuses are reliable. The fuse blows again immediately. The fuse continues to blow. You have got circuit breakers. The appliance has not got a fuse.   Check the main fuses. Leave the fuse box switched on. Fit another fuse. Check the fuse. Fit a new fuse. Look for scorch marks.  

 

LESSON 5

THE ELECTRIC MOTOR

Step 1.

List as many items as you can in the home, which use electric motors.

Reading skimming

A very useful strategy is reading a text quickly to get a general idea of the kind of information it contains. You can then decide which parts of the text are worth reading in more detail later, depending on your reading purpose. This strategy is called skimming.

 

Step 2.

Skim this text and identify the paragraphs, which contain information on each of these topics. The first one has been done for you.

a) What electric motors are used for paragraph 1?

b) Why the armature turns?

c) The commutator.

d) Electromagnets

e) Effect of putting magnets together.

f) The armature paragraph in an electric motor an electric current and magnetic field produce a turning movement. This can drive all sorts of machines from wrist-watches to trains. The motor that is used for example for a washing machine. It is an universal motor that can run on direct current or alternating current.

 

An electric current, running through a wire produces a magnetic field around the wire. If an electric current flows around a loop of wire with a bar of iron through it, the iron becomes magnetized. It is called electromagnets: one end becomes a North Pole and the other a South Pole, depending on which way the current is flowing around the loop.

If you put two magnets close together, like poles-torn example, two north poles - repel each other, and unlike poles attract each other. In a simple electric motor, a piece of iron with loops of wire round it, called an armature, is placed between the north and South poles of a stationary magnet known as the field magnet. When electricity flows around the armature wire, the iron becomes an electromagnet.

The attraction and repulsion between the poles of this armature magnet and the poles of the field magnet make the armature turn. As a result, its north pole is close to the south pole of the field magnet. Then the current is reversed so the north pole of the armature magnet becomes the South Pole. Once again, the attraction and repulsion between it and the field magnet make it turn. The armature continues turning as long as the direction of the current, and therefore its magnetic poles, keeps being reversed.

To reverse the direction of the current, the ends of the armature wire are connected to different halves of a split ring called a commutator.

Current flows to and from the commutator through small carbon blokes called brushes. As the armature turns, first one half of the commutator comes into contact with the brush delivering the current and then the other, so the direction of the current keeps being reversed.

Source: Adapted from I snide out: Electric Motor, Education Guardian.

 

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