Basic Electrical Engineering Questions and Answers – Capacitance and the Capacitor

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This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Capacitance and the Capacitor”.

1. Capacitor is a device used to__________
a) store electrical energy
b) vary the resistance
c) store magnetic energy
d) dissipate energy

Explanation: Capacitor is used to store the charge. It stores electrical energy between the plates.

2. Capacitor stores which type of energy?
a) kinetic energy
b) vibrational energy
c) potential energy
d) heat energy

Explanation: Capacitor store charge in between the plates. This charge is stationary so we can say capacitor store potential energy.

3. Capacitor blocks__________ after long time.
a) alternating current
b) direct current
c) both alternating and direct current
d) neither alternating nor direct current

Explanation: Capacitor blocks direct current at steady state and pass alternating current.
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4. Why does capacitor block dc signal at steady state?
a) due to high frequency of dc signal
b) due to zero frequency of dc signal
c) capacitor doesnot pass any current at steady state
d) due to zero frequency of dc signal

Explanation: Frequency of dc signal is zero. So, Capacitive reactance XC=1/2πfc becomes infinite and capacitor behaves as open circuit for dc signal. Hence, capacitor block dc signal.

5. If a parallel plate capacitor of plate area 2m2 and plate separation 1m store the charge of 1.77*10-11 C. What is the voltage across the capacitor?
a) 1V
b) 2V
c) 3V
d) 4V

Explanation: C=€0A/d
On substituting values of d, A, we get C=2€0.
Q=CV
V=1 V.

6. Which of the following is a passive device?
a) Transistor
b) Rectifier
c) Capacitor
d) Vaccuum Tubes

Explanation: Capacitor is a passive device as it consumes power rest all generate power so, they are active devices.

7. What is the value of capacitance of a capacitor which has a voltage of 4V and has 16C of charge?
a) 2F
b) 4F
c) 6F
d) 8F

Explanation: Q is directly proportional to V. The constant of proportionality in this case is C, that is, the capacitance. Hence Q=CV. From the relation, C=Q/V= 16/4=4F.

8. For which medium capacitance is high?
a) Air
b) Mica
c) Water
d) Metal

Explanation: Metals are assumed to have a high value of dielectric constant so they have high capacitance.

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