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

The total resistance in the circuit can be calculated by adding the resistances of the components in series:

$R_{total} = R_1 + R_2 = 20 \, \Omega + 10 \, \Omega = 30 \, \Omega$

Using Ohm's law, the potential difference (V) can be calculated:

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

The power output (P) can be calculated using the formula:

$P = I \times V$

Substituting the values gives:

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

Rounding to one significant figure, the power is:

$P = 5 \, W$