The diagram shows part of a circuit and the currents in the circuit - AQA - A-Level Physics - Question 23 - 2019 - Paper 1

The voltage across the 10 Ω resistor (V) can be found using the formula:

$V = I imes R$

Substituting the values:

$V = 2 ext{ A} imes 10 ext{ Ω} = 20 ext{ V}$

The total current entering the junction at point P is 2 A, and the current leaving is 4 A. Using the conservation of charge, the current through the 20 Ω resistor is:

$I = 4 ext{ A} - 2 ext{ A} = 2 ext{ A}$

The voltage across the 20 Ω resistor can also be calculated:

$V_{20} = I imes R = 2 ext{ A} imes 20 ext{ Ω} = 40 ext{ V}$

The total potential difference from point P to earth is the sum of the voltage across the 10 Ω resistor and the voltage across the 20 Ω resistor:

$V_{total} = V_{10} + V_{20} = 20 ext{ V} + 40 ext{ V} = 60 ext{ V}$

The potential difference between point P and earth is therefore 60 V, which corresponds to option A.