This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Charging and Discharging Currents”.

1. Which of the following charging and discharging of a capacitor?

a) Time constant

b) Current

c) Power

d) Voltage

View Answer

Explanation: The time constant in a circuit consisting of a capacitor is the product of the resistance and the capacitance. Smaller the time constant, faster is the charging and discharging rate and vice versa.

2. What is the initial current while charging a capacitor?

a) High

b) Low

c) 0

d) Cannot be determined

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Explanation: The initial current of a capacitor is very high because the voltage source will transport charges from one plate of the capacitor to the other plate.

3. What is the final current while charging a capacitor?

a) High

b) Zero

c) Infinity

d) Low

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Explanation: The final current is almost equal to zero while charging a capacitor because the capacitor is charged up to the source voltage.

4. 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

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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.

5. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the initial value of discharge current.

a) 10A

b) 0A

c) Infinity

d) 20A

View Answer

Explanation: When the capacitor is discharging the value of initial current is a finite one. The finite initial current value is found using ohm’s law: I=V/R= 400/20= 20A.

6. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the final value of discharge current.

a) 10A

b) 0A

c) Infinity

d) 20A

View Answer

Explanation: In a discharging circuit, the final voltage is equal to zero as all the positive and negative charges have combined. Since the voltage is equal to zero, the current is also equal to zero as voltage is directly proportional to current by ohm’s law.

7. When will be capacitors fully charged?

a) When voltage is zero

b) When the supply voltage is equal to the capacitor voltage

c) When voltage is infinity

d) When capacitor voltage is equal to half the supply voltage

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Explanation: When the capacitor voltage is equal to the source voltage, it means that all the charges have moved from one plate of the capacitor to the other.

8. What happens to the capacitor when the capacitor voltage is equal to the source voltage?

a) The charging phase of the capacitor is over

b) The discharging phase of the capacitor is over

c) The capacitor is switched off

d) The capacitor is switched on

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Explanation: When the capacitor voltage is equal to the source voltage, it means that all the charges have moved from one plate of the capacitor to the other. Hence the capacitor is charged and the charging phase is over.

9. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the final value of charging current.

a) 10A

b) 0A

c) Infinity

d) 20A

View Answer

Explanation: The final value of charging current in a capacitor is equal to the initial value of discharging current in it. Hence the final value of charging current is: Vc/R=20A.

10. A capacitor is charged to a voltage of 400V and has a resistance of 20ohm. Calculate the initial value of charging current.

a) 10A

b) 0A

c) Infinity

d) 20A

View Answer

Explanation: Initially, there’s 0V voltage in a capacitor. As the capacitor charges, the voltage increases. Since voltage is proportional to current by ohm’s law, initial current is also equal to zero.

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

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