CAIE A-Level Physics 9.1.3 Using Q = It

Practise using Q = It to calculate charge, current or time, converting charge to carrier number and interpreting accumulated charge in graphs.

Exam points

calculate charge, current or time using Q = It with consistent units
convert charge into a number of charge carriers, or infer current from a stated particle beam or carrier rate
interpret current and charge in graphs or changing-current situations when the accumulated charge must be determined

[Maximum number: 2]

A battery of electromotive force (e.m.f.) E and internal resistance r is connected to a variable resistor of resistance R, as shown in Fig. 6.1.

Fig. 6.1

The current in the circuit is I and the potential difference across the variable resistor is V.

The battery stores 9.2 kJ of energy. The variable resistor is adjusted so that $V=2.1 \mathrm{~V}$ . Use Fig. 6.2 to:

calculate the number of conduction electrons moving through the battery in a time of 1.0 s

number =

$\begin{aligned} \text { number } =0.50 / 1.60 \times 10^{-19} =3.1 \times 10^{18} \end{aligned}$

A1

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