2022 · Specimen · 9702/02 | Q6

0/32parts marked · 0 of 53 marks

Question (6 of 7)9 marks · Practise this topic →

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Available practice: 53 of 60 marks. Parts 2(b)(iv), 4(b)(iii), 6(b)(v) await marking support. Scores cover available parts only.

Three resistors of resistances R₁, R₂ and R₃ are connected as shown in Fig. 6.1.

The currents in the resistors are I₁, I₂ and I₃. The total current in the combination of resistors is I and the potential difference across the combination is V.

Show that the total resistance R of the combination is given by the equation

(a)1/R = 1/R₁ + 1/R₂ + 1/R₃.

Fig. 6.1 — see the question text for what it shows

Answer guidance

Show The result is given, so every step of the reasoning is what earns the marks.

[2 marks]

A battery of electromotive force (e.m.f.) 6.0 V and internal resistance r is connected to an external resistor of resistance 12 Ω and a thermistor X, as shown in Fig. 6.2.

(b)(i)By considering energy, explain why the potential difference across the terminals of the battery is less than the e.m.f.

Fig. 6.2 — see the question text for what it shows

[1 mark]

A battery of electromotive force (e.m.f.) 6.0 V and internal resistance r is connected to an external resistor of resistance 12 Ω in parallel with a thermistor X.

A charge of 2.5 kC passes through the battery.

Calculate:

• the total energy transferred by the battery

(b)(ii)• the number of electrons that pass through the battery.

Answer guidance

Calculate Show your working. The method can earn marks even when the final value is wrong, and a bare answer often cannot.

[3 marks]

A battery of e.m.f. 6.0 V and internal resistance r is connected to an external resistor of resistance 12 Ω and a thermistor X in parallel.

The combined resistance of the external resistor and thermistor X connected in parallel is 4.8 Ω.

(b)(iii)Calculate the resistance of X.

Answer guidance

Calculate Show your working. The method can earn marks even when the final value is wrong, and a bare answer often cannot.

[1 mark]

A 12 Ω resistor is connected in parallel with a thermistor X; the combined resistance is 4.8 Ω, so the resistance of X can be found (as in (b)(iii)).

Use your answer in (b)(iii) to determine the ratio

(b)(iv)(power dissipated in thermistor X)/(power dissipated in 12 Ω resistor).

Answer guidance

Using You must use the thing it names. An answer that reaches the right value another way may not score.

[2 marks]

9702/02/SP/22Cambridge International AS & A Level Physics 9702 · Specimen 2022 · Paper 2 · Question 6