Physics 5054 · O Level · Series and parallel circuits

Series and parallel circuits — practice question

A student carries out an investigation into the resistance of two resistors. Fig. 2.1 illustrates the apparatus used to determine the current $I$ through resistor X and the potential difference $V$ across it.
(a)[2]

Draw a circuit diagram for the setup illustrated in Fig. 2.1.

(b(i))[2]

Calculate the resistance $R_Y$ of resistor Y and complete Table 2.1. Use the equation: $resistance = \frac{V}{I}$ Give your answer to the nearest whole number.

(b(ii))[1]

The student joins resistors X and Y in a parallel arrangement. He uses this combination in the circuit in Fig. 2.1 instead of the single resistor Y. Fig. 2.2 shows the ammeter reading for the parallel arrangement. Record the reading of $I$ shown in Fig. 2.2.

(b(iii))[1]

The potential difference remains at $1.0\,\text{V}$. Using the value of $I$ in (b)(ii) and the equation in (b)(i), calculate the resistance $R_C$ of the parallel combination.

(c)[1]

Theory predicts that the resistance $R_C$ of the two resistors X and Y connected in parallel is given by: $R_C = \frac{R_X R_Y}{R_X + R_Y}$ State, giving a reason, whether your value for $R_C$ in (b)(iii) agrees with this prediction.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: One closed series circuit with battery, resistor, ammeter and switch

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