Physics 9702 · AS & A Level · Kirchhoff's laws

Kirchhoff's laws — practice question

(a(i))[1]

State what Kirchhoff’s first law says.

(a(ii))[1]

Kirchhoff’s first law is associated with conservation of a particular quantity. State what this quantity is.

(b)

A variable resistor with resistance $R$ is included to regulate the current in the circuit, as shown in Fig. 5.1. The generator $G$ has e.m.f. $20\,\text{V}$ and internal resistance $0.50\,\Omega$. The battery has e.m.f. $12\,\text{V}$ and internal resistance $0.10\,\Omega$. The current in the circuit is $2.0\,\text{A}$.

(b(i))[2]

Use Kirchhoff’s second law for the circuit to find $R$.

(b(ii))[2]

Calculate the total power output of $G$.

(b(iii))[2]

Calculate the power dissipated in the total resistance of the circuit.

(b(iv))[2]

The circuit transfers energy from the generator to the battery. Determine the efficiency of the circuit.

(iii)[2]

Calculate the power dissipated in the circuit’s total resistance.

(iv)[2]

Energy is supplied from the generator to the battery in this circuit. Determine the efficiency of the circuit.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: The total current entering a junction equals the total current leaving it

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