This set of Basic Electrical Engineering Assessment Questions and Answers focuses on “Current and Voltage in a Capacitive Circuit”.

1. What happens to the voltage in a capacitive circuit when the frequency increases?

a) Increases

b) Decreases

c) Remains the same

d) Becomes zero

View Answer

Explanation: The capacitive reactance decreases as the frequency increases since they are in-versely proportional. The voltage is directly proportional to the capacitive reactance, hence it de-creases.

2. When voltage across a capacitor increases, what happens to the charge stored in it?

a) Increases

b) Decreases

c) Becomes zero

d) Cannot be determined

View Answer

Explanation: When voltage across a capacitor increases, the charge stored in it also increases be-cause charge is directly proportional to voltage, capacitance being the constant of proportionality.

3. What happens to the current flow in a fully charged capacitor?

a) Current flow stops

b) Current flow doubles

c) Current flow becomes half its original value

d) Current flow becomes one-fourth its original value

View Answer

Explanation: When a capacitor is fully charged, it does not store any more charge.There is no change in charge with time. Current is the rate of change of charge, hence it becomes zero, or stops.

4. What is the correct formula for capacitive reactance?

a) Xc=1/(2*f*pi*C)

b) Xc=(2*f*pi*C)

c) Xc=1/(f*pi*C)

d) Xc=I/(2*f*pi*C)

View Answer

Explanation: The capacitive reactance Xc is the reciprocal of the product of the angular velocity and the capacitance. The angular velocity=2*pi*f, therefore Xc=1/(2*f*pi*C).

5. Calculate the capacitance of a capacitor that stores 80microC of charge and has a voltage of 4V.

a) 20F

b) 20microF

c) 10F

d) 10microF

View Answer

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

C=80microC/4V=20microF.

6. What happens to the current in a capacitive circuit when the frequency increases?

a) Increases

b) Decreases

c) Remains the same

d) Becomes zero

View Answer

Explanation: The capacitive reactance decreases as the frequency increases since they are in-versely proportional. The current is inversely proportional to the capacitive reactance, hence it in-creases.

7. Calculate the current in the capacitor having 2V supply voltage and 3F capacitance in 2seconds.

a) 2A

b) 5A

c) 6A

d) 3A

View Answer

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

Q=3*2=6C.

I=Q/t= 6/2=3A.

8. If 2V is supplied to a 3F capacitor, calculate the charge stored in the capacitor.

a) 1.5C

b) 6C

c) 2C

d) 3C

View Answer

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

Q=3*2=6C.

9. A 30 microF capacitor is connected across a 400V, 50Hz supply. Calculate the capacitive reac-tance.

a) 102 ohm

b) 123.4 ohm

c) 106.2 ohm

d) 143.2 ohm

View Answer

Explanation: We know that: Xc=1/(2*f*pi*C).

Substituting the values from the given question, we get Xc= 106.2 ohm.

10. A 30 microF capacitor is connected across a 400V, 50Hz supply. Calculate the current.

a) 6.67A

b) 3.77A

c) 5.65A

d) 2.33A

View Answer

Explanation: We know that: Xc=1/(2*f*pi*C).

Substituting the values from the given question, we get Xc= 106.2 ohm.

I=V/Xc, hence I= 3.77A.

**Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.**

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