CAIE A-Level Physics 10.2.6 Combined Resistance in Parallel

Practise calculating equivalent resistance, current and potential difference in parallel resistor networks, applying the formula with consistent units and checking branch values.

Exam points

calculate equivalent resistance, current or p.d. for two or more resistors in parallel
apply the parallel-resistance formula with consistent units and identify branch currents or p.d.

[Maximum number: 1]

A battery of electromotive force (e.m.f.) 6.0 V and internal resistance r is connected to a resistor of resistance $12 \Omega$ and a variable resistor X, as shown in Fig. 6.2.

Fig. 6.2

The combined resistance of the two resistors connected in parallel is $4.8 \Omega$ .

Calculate the resistance of X.

\text { resistance of } X=

$\begin{aligned} 1 / 4.8=1 / 12+1 / R_{\mathrm{X}} R_{\mathrm{X}}=8.0 \Omega \end{aligned}$

A1

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10.2.6—The formula for the combined resistance of two or more resistors in parallel question 1