ConceptConceptDocsDocuments

CAIE A-Level Physics 19.2 Energy Stored in a Capacitor

Practise deriving capacitor energy from the area under a Q-V graph and comparing W = 1/2 QV with equivalent capacitance formulae.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • determine capacitor energy from the potential–charge graph area
  • calculate and compare stored energy using W=1/2QV=1/2CV²

Covered syllabus points

19.2.1—The electric potential energy stored in a capacitor19.2.2—W = 1/2 QV = 1/2 CV 2

19.2 Energy stored in a capacitor question 1

[Maximum number: 3]

The variation with potential difference V of the charge Q on one of the plates of a capacitor is shown in Fig. 5.1.

Fig. 5.1

Fig. 5.1

The capacitor is connected to an 8.0 V power supply and two resistors R and S as shown in Fig. 5.2.

Fig. 5.2

Fig. 5.2

The resistance of R is 25kΩ25 \mathrm{k} \Omega and the resistance of S is 220kΩ220 \mathrm{k} \Omega.
The switch can be in either position X or position Y .

The switch is in position X so that the capacitor is fully charged.

Calculate the energy E stored in the capacitor.

E=

19.2 Energy stored in a capacitor question 2

[Maximum number: 3]

A battery of e.m.f. 12 V and negligible internal resistance is connected to a network of two capacitors and a resistor, as shown in Fig. 7.2.

Fig. 7.2

Fig. 7.2

The capacitors have capacitances of 200μ F200 \mu \mathrm{~F} and 600μ F600 \mu \mathrm{~F}. The switch has two positions, A and B.

The switch is now moved from position A to position B.

Calculate the potential difference across the 600μ F600 \mu \mathrm{~F} capacitor when it has discharged 50 % of its initial energy.
potential difference = V

All question bank results loaded