CAIE IGCSE Physics Potential Difference V = W/Q

Practise using V = W/Q to connect potential difference, energy transfer and charge, including unit equivalence and multi-step lightning or circuit calculations.

Exam points

use V = W/Q and rearrange it to calculate potential difference, energy transferred or charge
recognise one volt as one joule per coulomb and apply that meaning to each coulomb transferred
convert megajoules or other prefixes before substituting values in lightning and circuit contexts

[Maximum number: 2]

Fig. 10.1 shows a lightning flash between a cloud and the ground beneath.

Fig. 10.1

The charge built up on the cloud before the lightning flash is 0.60 C . This charge is completely transferred to the ground by the lightning flash in $5.0 \times 10^{-5} \mathrm{~s}(0.000050 \mathrm{~s})$ .

The potential difference (p.d.) between the cloud and the ground during the lightning flash is $2.5 \times 10^{8} \mathrm{~V}$ .

Calculate the energy transferred during the lightning flash.

energy =

(E=) I V t OR $12000 \times 2.5 \times 10^{8} \times 0.000050$

C1

$1.5 \times 10^{8} \mathrm{~J}$

A1

OR

(E=) QV OR $0.60 \times 2.5 \times 10^{8}$

(C1)

$1.5 \times 10^{8} \mathrm{~J}$

(A1)

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4.2.3.7—P.d.: V = W/Q question 1