Edexcel IGCSE Physics 2.19 Series circuit calculations

Practise using series circuit rules to calculate missing voltages and resistances, then explain brightness changes in lamps, LDRs and thermistors.

Exam points

use V = IR and series voltage addition to find a missing p.d. across one resistor
calculate total resistance, then subtract a thermistor or fixed resistor value
explain lamp brightness changes from voltage share, current and resistance in series

[Maximum number: 4]

The circuit diagram shows a light dependent resistor (LDR) and a $73 \Omega$ resistor connected in series with a 1.5 V cell.

(a)

Calculate the voltage across the LDR.

voltage = ............ V

[ 2 ]

(b)

The graph shows how the resistance of the LDR changes with light intensity.

[ 2 ]

(i)

Explain why the voltage across the LDR decreases when the resistance of the LDR decreases.

[ 2 ]

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