An electrical circuit is shown in Figure 3 - AQA - GCSE Physics - Question 3 - 2018 - Paper 1

To find the potential difference (V), we first need to calculate the total resistance in the circuit. The resistors of 20 Ω and 10 Ω are in series, so their total resistance is:

$R_{total} = 20 \, \Omega + 10 \, \Omega = 30 \, \Omega$

Using Ohm's Law, the potential difference can be calculated as:

$V = I \times R_{total} = 0.4 \, A \times 30 \, \Omega = 12 \, V$

Power (P) can be calculated using the formula:

$P = current \times potential \, difference$

Substituting the values we have:

$P = 0.4 \, A \times 12 \, V = 4.8 \, W$

Rounding this to one significant figure, we get:

$P \approx 5 \, W$