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CAIE A-Level Physics 9.2.3 Electrical Power

Practise selecting P = VI, P = I²R or P = V²/R for a component, using the circuit data to calculate power and compare how different quantities affect the result.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • choose and apply P = VI, P = I²R or P = V²/R for the quantities given
  • calculate electrical power, current, voltage or resistance and rearrange the relevant expression
  • compare power and energy transfer in components, including unit conversion and time where required
  • recognise when two power expressions are equivalent only under the stated V–I–R relationship

9.2.3—P = VI, P = I 2R and P = V 2 / R question 1

[Maximum number: 2]

Fig. 5.2 shows a circuit with a battery of electromotive force (e.m.f.) 12.0 V connected to a linear potentiometer AB and two identical filament lamps P and Q .

Fig. 5.2

Fig. 5.2

The battery has negligible internal resistance and the lamps each have the same I-V characteristic shown in Fig. 5.1.

When the slider of the potentiometer is at its midpoint, as shown in Fig. 5.2, the current I in the battery is 1.78 A .

Determine:

the total power dissipated in lamps P and Q
total power = W

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