CAIE IGCSE Physics 4.3.2.4 Combined Resistance of Two or More Questions

Learn to add series resistances, simplify branches, and use V = IR for circuit values.

Exam points

add series resistances using R_total = R1 + R2 + ...
reduce a series branch before handling parallel sections
use combined series resistance with V = IR to find current or unknown resistance

[Maximum number: 3]

Fig. 10.1 shows a circuit containing a filament lamp of resistance $0.30 \Omega$ and two resistors, each of resistance $0.20 \Omega$ .

Fig. 10.1

Calculate the combined resistance of the lamp and the two resistors.
resistance =

$1 / \mathrm{R}_{\mathrm{p}}=1 / \mathrm{R}_{1}+1 / \mathrm{R}_{2} \mathrm{OR}\left(\mathrm{R}_{\mathrm{p}}=\right) 1 /\left(1 / \mathrm{R}_{1}+1 / \mathrm{R}_{2}\right) \mathrm{OR}\left(\mathrm{R}_{\mathrm{p}}=\right) \mathrm{R}_{1} \mathrm{R}_{2} /\left(\mathrm{R}_{1}+\mathrm{R}_{2}\right) \mathrm{OR}(0.2 \times 0.3) /(0.2+0.3) \mathrm{OR} 0.6 \times 0.2$ $\left(\mathrm{R}_{\mathrm{p}}=\right) 0.12(\Omega)$ $\left(\mathrm{R}_{\mathrm{t}}=0.12 \Omega+0.20 \Omega=\right) 0.32 \Omega$

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CAIE IGCSE Physics 4.3.2.4 Combined Resistance of Two or More Questions question 1