CAIE IGCSE Physics 4.2.4.1 Resistance: R = V/I

Practise applying R = V/I to resistors, lamps and circuits, using p.d. and current values from diagrams, tables and graph prompts.

Exam points

calculate resistance, current or p.d. after selecting the correct V and I from a circuit
use R = V/I with series or parallel reasoning when current is split or total resistance is needed
sketch or interpret how current changes as resistance varies for a fixed supply

[Maximum number: 2]

Fig. 7.1 shows three identical lamps and an ammeter connected to a power supply.

Fig. 7.1

The switches are closed. Each lamp is rated at 60 W and operates at its normal working voltage of 110 V .

Calculate the resistance of the filament of one of the lamps when working normally.

resistance =

I=V / R in any form OR(R=) V / I
$\mathrm{OR}(R=) V^{2} / P \text { OR }(R=) P / I^{2}$

C1

$(R=110 / 0.55=) 200 \Omega$

A1

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