Discharge of Capacitor MCQ [Free PDF] - Objective Question Answer for Discharge of Capacitor Quiz

21. If the charge stored in a capacitor is 4C and the value of capacitance is 2F, calculate the energy stored in it.

A. 2J
B. 4J
C. 8J
D. 16J

Answer: B

The expression for finding the value of capacitor energy is:

U = Q²/2C = 4 × 4/(2 × 2) = 4J.

22. If the charge in a capacitor is 4C and the energy stored in it is 4J, find the value of capacitance.

A. 2F
B. 4F
C. 8F
D. 16F

Answer: A

The expression for finding the value of capacitance energy is:

U = Q²/2C.

Substituting the values of U and Q, we get C = 2F.

23. If the charge in a capacitor is 4C and the energy stored in it is 4J, calculate the voltage across its plates.

A. 2V
B. 4V
C. 8V
D. 16V

Answer: A

The expression for finding the value of capacitor energy is:

U = Q²/2C.

Substituting the values of U and Q, we get C = 2F.

V = Q/C, hence V = 4/2 = 2V.

24. Calculate the energy in the 2F capacitor in the given circuit below.

A. 8.6kJ
B. 64kJ
C. 64J
D. 6.4kJ

Answer: D

From the expression value of capacitor energy is

WD = CV²/2

= 2 × 802/2 = 6400J = 6.4kJ.

25. Calculate the energy in the 4F capacitor in the given circuit below.

A. 128kJ
B. 1.28kJ
C. 12.8kJ
D. 1280J

Answer: C

From the expression of capacitor energy

WD = CV²/2

= 4 × 802/2 = 12800J = 12.8kJ.

26. Calculate the energy stored in the combination of the capacitors.

A. 192kJ
B. 1.92kJ
C. 19.2kJ
D. 1920J

Answer: C

The equivalent capacitance is: Ceq = 4+2 = 6F.

From the expression of capacitor energy

WD = CV²/2

= 6 × 802/2 = 19200J = 19.2kJ.

27. Which of the following is the correct expression for the force between the plates of a parallel plate capacitor?

A. F = ε × A × (V/x)²/2
B. F = ε × A × (V/x)²/3
C. F = ε (V/x)²/2
D. F = ε (V/x)²/3

Answer: A

The force is proportional to the square of the potential gradient and the area.

Hence the force F = ε × A × (V/x)²/2.

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