Edexcel IGCSE Physics 2.19 Series Circuit Calculations Questions

Apply Ohm’s law and voltage addition in series to find component values, then use the circuit results to compare lamp brightness.

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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