electricity paper 6

8/11/2019 Electricity Paper 6

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PREPARED BY PREETI MANOJ

1. The IGCSE class is investigating the resistance of a wire. The circuit is as shown in Fig. 1.1.

FIG.1.1

(a) A student uses the switches to connect the wireABinto the circuit and records the p.d. Vacross the wire

betweenAand B. He also records the current Iin the wire.The student then repeats the measurements using the wire CDin place of wireAB.The readings are shown in the table below.

(i) Calculate the resistance Rof each wire, using the equationR= V/I.Record the values in the table.

(ii) Complete the column headings in the table.


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[3]

2. The IGCSE class is comparing the combined resistance of resistors in different circuit arrangements. Thefirst circuit is shown in Fig. 2.1.

(a) The current Iin the circuit and the p.d. Vacross the three resistors are measured and recorded. Threemore circuit arrangements are used. For each arrangement, a student disconnects the resistors and thenreconnects them between pointsAand Bas shown in Figs. 2.22.4.

The voltage and current readings are shown in the Table 2.1.


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(i) Complete the column headings for each of the V, Iand Rcolumns of Table 2.1.

(ii) For each circuit, calculate the combined resistance Rof the three resistors using the equationR= V/ I

. Record these values of Rin Table 2.1. [3]

(b) Theory suggests that, if all three resistors have the same resistance under all conditions, the combinedresistance in circuit 1 will be one half of the combined resistance in circuit 2.

(i) State whether, within the limits of experimental accuracy, your results support this theory. Justify youranswer by reference to the results.

statement ........................................................................................................................................................

justification .........................................................................................................................................................

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(ii) Suggest one precaution you could take to ensure that the readings are as accurate as possible.

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....................................................................................................................................................................... [3]

3. The IGCSE class is investigating the resistance of a wire.The circuit is shown in Fig. 3.1.


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ABis a resistance wire. The students place the sliding contact Con the resistance wireAB at a distance x=0.100 m fromA. They switch on and measure the p.d. Vacross the wire betweenAand C. They also measurethe current Iin the wire. The value of Iis 0.38 A.They repeat the procedure several times using differentvalues of x. The readings are shownin Table 3.1. The current Iis 0.38 A for each value of x.

a)Calculate the resistance Rof the sectionACof the wire for each value of xusing the equation R= V/I.Record the values of Rin the table.(b) Use the results in Table 3.1 to plot a graph of R/ (y-axis) against x/ m (x-axis). Draw the best fit line.


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(c) Within the limits of experimental accuracy, what do you conclude about the variation of resistance withdistance along the wire? Justify your conclusion by reference to your graph.

statement .............................................................................................................................................................

justification .........................................................................................................................................................

...................................................................................................................................................................... [2]

(d) Using your graph, determine the value for Rwhen x= 0.750 m. Show clearly on your graph how youobtained the necessary information.

R= ....................................... [2]

(e) A variable that may be difficult to control in this experiment is the heating effect of the current, which affectsthe resistance of the wire. Suggest how you would minimise the heating effect.

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..................................................................................................................................... .................................... [1]


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4. A student is investigating the relationship between potential difference V across a resistor and the current

I in it. Fig. 4.1 shows the apparatus that the student is using.

FIG.4.1

(a) Draw the circuit diagram of the circuit shown in Fig. 4.1. Use standard circuit symbols.

[3]

(b) The student is using a lamp to show when the current is switched on.Why is it unnecessary to use thelamp?


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(c) State which piece of apparatus in the circuit is used to control the size of the current.

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(d) The student removes the lamp from the circuit. He is told that the resistance of a conductor is constant ifthe temperature of the conductor is constant. He knows that the current in the resistor has a heating effect.Suggest two ways in which the student could minimise the heating effect of the current in the resistor.

1................................................................................................................................................................................

2. ...................................................................................................................................................................... [2]

(e) Fig. 4.2 shows a variable resistor with the sliding contact in two different positions.


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FIG.4.2

State which position, A or B, shows the higher resistance setting. Explain your answer.

statement ...................................................................................................................................................

explanation .................................................................................................................................................

.................................................................................................................................................................... [1]


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5. The IGCSE class is investigating the potential difference across, and the current in, wires. The apparatus isshown in Fig. 5.1.

fig.5.1a) Draw a circuit diagram of the apparatus. Use standard circuit symbols. (The circuit includes two identicalresistance wiresABand CD. Use the standard symbol for a resistance to represent each of these wires.)

This circuit is called circuit 1.

[3]

For circuit 1, the student places the contact Son the resistance wireABat a distance of 0.500m fromA. He

measures the p.d. Vacross the wire betweenAand Sand the current Iin the circuit.The student then records the measurements for circuits 2 and 3, shown in Fig. 5.2 and Fig. 5.3.


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fig.5.2

fig.5.3

The voltage Vand current Ifor all three circuits are shown in Table 5.1.

table 5.1


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(b) Complete the column headings in the table. [1]

c) Theory suggests that,1. in circuits 1 and 2, the values of potential difference Vwill be equal,2. the value of potential difference Vin circuit 3 will be half that in circuit 1 or circuit 2.

(i) State whether, within the limits of experimental accuracy, the results support these predictions.

Justify your statement by reference to the results.

Prediction 1 ............................................................................................................................................................

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Prediction 2 ...........................................................................................................................................................

......................................................................................................................................................................... [2]

(ii) Suggest one reason, other than a change in temperature of the wires, why the results may not support thetheory.

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....................................................................................................................................................................... [1]

electricity paper 6

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