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 inversely proportional. The voltage is directly proportional to the capacitive reactance, hence it decreases.

2. 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).

3. 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.

4. 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 inversely proportional. The current is inversely proportional to the capacitive reactance, hence it increases.

5. 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.

6. A 30 microF capacitor is connected across a 400V, 50Hz supply. Calculate the capacitive reactance.

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.

7. 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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