Physics

Capacitors and Capacitance

189 Questions

Capacitors and capacitance are crucial topics in physics, covering the storage of electric charge and energy. These concepts explore series and parallel combinations, dielectric materials, and capacitive reactance. Questions frequently appear in various competitive engineering and medical entrance exams.

Series and parallel capacitorsParallel plate capacitorsCapacitive reactance formulasDielectrics and permittivitySpherical capacitors

Capacitors and Capacitance Questions

Multiple choice

A dielectric material is inserted between the plates of a capacitor. What happens to the capacitance?

  1. Increases

  2. Decreases

  3. Remains the same

  4. Cannot be determined
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When a dielectric material is inserted between the plates of a capacitor, the capacitance increases because the dielectric material reduces the electric field between the plates.

Multiple choice

What is the function of a dielectric material in a capacitor?

  1. To increase the capacitance

  2. To decrease the capacitance

  3. To prevent the flow of current between the plates

  4. To store electrical energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The function of a dielectric material in a capacitor is to increase the capacitance by reducing the electric field between the plates.

Multiple choice

The capacitance of a capacitor is 10 μF. What is the charge stored on the capacitor when the voltage across it is 12 V?

  1. 120 μC

  2. 240 μC

  3. 360 μC

  4. 480 μC
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The charge stored on a capacitor is given by the equation Q = CV, where Q is the charge, C is the capacitance, and V is the voltage. Substituting the given values, we get Q = 10 μF * 12 V = 120 μC.

Multiple choice

A capacitor is charged to a voltage of 10 V. What is the energy stored in the capacitor if its capacitance is 20 μF?

  1. 100 μJ

  2. 200 μJ

  3. 300 μJ

  4. 400 μJ
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The energy stored in a capacitor is given by the equation E = 1/2 CV^2, where E is the energy, C is the capacitance, and V is the voltage. Substituting the given values, we get E = 1/2 * 20 μF * (10 V)^2 = 100 μJ.

Multiple choice

What is the relationship between the capacitance of a capacitor and the frequency of an AC circuit?

  1. Capacitance is directly proportional to frequency

  2. Capacitance is inversely proportional to frequency

  3. Capacitance is independent of frequency

  4. Capacitance varies sinusoidally with frequency
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The capacitance of a capacitor is inversely proportional to the frequency of an AC circuit.

Multiple choice

What is the effect of temperature on the capacitance of a capacitor?

  1. Capacitance increases with increasing temperature

  2. Capacitance decreases with increasing temperature

  3. Capacitance remains constant with changing temperature

  4. Capacitance varies randomly with temperature
Reveal answer Fill a bubble to check yourself
Correct answer
Explanation

The capacitance of a capacitor varies with temperature, depending on the material used as the dielectric.

Multiple choice

Which of the following factors does NOT affect the capacitance of a capacitor?

  1. Area of the plates

  2. Distance between the plates

  3. Permittivity of the material between the plates

  4. Shape of the plates
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The shape of the plates does not affect the capacitance of a capacitor.

Multiple choice

A capacitor is made of two parallel plates, each with an area of 10 cm^2. The distance between the plates is 1 mm. If the permittivity of the material between the plates is 8.85 x 10^-12 F/m, what is the capacitance of the capacitor?

  1. 8.85 pF

  2. 17.7 pF

  3. 26.5 pF

  4. 35.4 pF
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The capacitance of a parallel-plate capacitor is given by the equation C = εA/d, where ε is the permittivity of the material between the plates, A is the area of the plates, and d is the distance between the plates. Substituting the given values, we get C = (8.85 x 10^-12 F/m) * (10 cm^2) / (1 mm) = 8.85 pF.

Multiple choice

A capacitor is charged to a voltage of 10 V and then disconnected from the battery. After some time, the voltage across the capacitor drops to 8 V. What is the energy lost by the capacitor?

  1. 20 μJ

  2. 40 μJ

  3. 60 μJ

  4. 80 μJ
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The energy lost by a capacitor is given by the equation E = 1/2 C(V1^2 - V2^2), where E is the energy, C is the capacitance, V1 is the initial voltage, and V2 is the final voltage. Substituting the given values, we get E = 1/2 * C * (10 V)^2 - (8 V)^2 = 20 μJ.