CAIE A-Level Physics 10.1.3 Electromotive Force

Practise defining e.m.f. as energy supplied per unit charge, then calculating source e.m.f. and energy transferred using E = W/Q.

Exam points

define the e.m.f. of a source as energy transferred per unit charge in driving charge around a complete circuit
calculate or interpret source e.m.f. and the energy transferred when charge passes through a source

[Maximum number: 3]

A battery of electromotive force (e.m.f.) 6.0 V and internal resistance r is connected to a resistor of resistance $12 \Omega$ and a variable resistor X, as shown in Fig. 6.2.

Fig. 6.2

A charge of 2.5 kC passes through the battery.

Calculate
1. the total energy transformed by the battery,
energy = J
2. the number of electrons that pass through the battery.
number =

1

Energy = EQ

C1

$\begin{aligned} =6.0 \times 2.5 \times 10^{3} =1.5 \times 10^{4} \mathrm{~J} \end{aligned}$

A1

6(b)(ii)2

$\begin{aligned} \text { number } =2.5 \times 10^{3} / 1.6 \times 10^{-19} =1.6 \times 10^{22}\left(1.56 \times 10^{22}\right) \end{aligned}$

A1

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10.1.3—The electromotive force (e.m.f.) of a source as energy transferred per unit question 1