1. What is the relation between current and voltage in a capacitor?
A. I = 1/C × ∫(Vdt)
B. I = CdV/dt
C. I = 1/CdV/dt
D. I = Ct
Answer: B
Current = rate of change of charge
I = dQ/dt. Q = CV
C(capacitance) is constant for a given capacitor so
I = CdV/dt.
2. If 2V is supplied to a 3F capacitor, calculate the charge stored in the capacitor.
A. 1.5C
B. 6C
C. 2C
D. 3C
Answer: B
In a capacitor, 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.
3. Calculate the current in the capacitor having 2V supply voltage and 3F capacitance in 2 seconds.
A. 2A
B. 5A
C. 6A
D. 3A
Answer: D
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.
4. A 4 µF capacitor is charged to 120V, the charge in the capacitor would be?
A. 480C
B. 480 µC
C. 30C
D. 30 µC
Answer: B
Q is directly proportional to V.
The constant of proportionality, in this case, is C, that is, the capacitance.
Hence Q = CV.
Q = 4 × 120 = 480 µC.
5. For high frequencies, capacitor acts as _________
A. Open circuit
B. Short circuit
C. Amplifier
D. Rectifier
Answer: B
Capacitive impedance is inversely proportional to frequency. Hence at very high frequencies, the impedance is almost equal to zero, hence it acts as a short circuit and there is no voltage across it.
6. For very low frequencies, capacitor acts as ________
A. Open circuit
B. Short circuit
C. Amplifier
D. Rectifier
Answer: A
Capacitive impedance is inversely proportional to frequency. Hence at very low frequencies the impedance is almost infinity and hence acts as an open circuit and no current flows through it.
7. A capacitor consists of _________
A. Two conductors
B. Two semiconductors
C. Two dielectrics
D. Two insulators
Answer: A
A capacitor consists of two conductors connected in parallel to each other so that it can store charge in between the plates.
8. Capacitor preferred when there is high frequency in the circuits is __________
A. Electrolyte capacitor
B. Mica capacitor
C. Air capacitor
D. Glass capacitor
Answer: B
Mica capacitors are preferred for high-frequency circuits because they have low ohmic losses and less reactance.
9. Capacitance increases with ________
A. Increase in plate area
B. Decrease in plate area
C. Increase in distance between the plates
D. Increase in the density of the material
Answer: A
Capacitance is directly proportional to the plate area. Hence as the plate area increases, the capacitance also increases.
10. Capacitance increases with __________
A. Increase in distance between the plates
B. Decrease in plate area
C. Decrease in distance between the plates
D. Increase in the density of the material
Answer: C
Capacitance is inversely proportional to the distance between the two parallel plates. Hence, as the distance between the plate decreases, the capacitance increases.
11. Which among the following expressions relates the charge, voltage, and capacitance of a capacitor?
A. Q = C/V
B. Q = V/C
C. Q = CV
D. C = Q2V
Answer: C
Q is directly proportional to V. The constant of proportionality, in this case, is C, that is, the capacitance.
Hence Q = CV.
12. If a 2F capacitor has a 1C charge, calculate the voltage across its terminals.
A. 0.5V
B. 2V
C. 1.5V
D. 1V
Answer: A
Q is directly proportional to V. The constant of proportionality, in this case, is C, that is, the capacitance.
Hence Q = CV
V = Q/C = 1/2 V = 0.5V.
13. What is the voltage across a capacitor at the time of switching, that is, when t = 0?
A. Infinity
B. 0V
C. Cannot be determined
D. 1V
Answer: B
At the time of switching, when t = 0, the capacitor acts as a short circuit. The voltage across a short is always equal to zero hence the voltage across the capacitor is equal to zero.
14. What is the voltage across the capacitor if the switch is closed and a steady state is reached?
A. 8V
B. 0V
C. 10V
D. Infinity
Answer: C
When a steady state is reached, the capacitor acts as an open circuit and the 10V is connected in parallel to it.
Hence Vc = 10V.
15. If one plate of a parallel plate capacitor is charged to a positive charge the other plate is charged to?
A. Positive
B. Negative
C. Positive or negative
D. Not charged
Answer: B
If one plate is charged to positive, the other plate is automatically charged to negative so that it can store the electrical charge.
16. When the voltage across a capacitor increases, what happens to the charge stored in it?
A. Increases
B. Decreases
C. Becomes zero
D. Cannot be determined
Answer: A
When the voltage across a capacitor increases, the charge stored in it also increases because a charge is directly proportional to voltage, capacitance being the constant of proportionality.
17. When will the capacitor fully charge?
A. When the voltage across its plates is half the voltage from the ground to one of its plates
B. When the current through the capacitor is a 1/root2 time its value
C. When the supply voltage is equal to the capacitor voltage
D. Never
Answer: C
The capacitor will be fully charged when the capacitor voltage is equal to the supply voltage the current stops flowing through the circuit and the charging phase is over.
18. 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 of its original value
Answer: A
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.
19. Calculate the capacitance of a capacitor that stores 40µC of charge and has a voltage of 2V.
A. 20F
B. 20 µF
C. 10F
D. 10 µF
Answer: B
In a capacitor, Q is directly proportional to V.
The constant of proportionality, in this case, is C, that is, the capacitance.
Hence C = Q/V.
C = 40µC/2V = 20 µF.
20. What happens to the capacitance when the voltage across the capacitor increases?
A. Decreases
B. Increases
C. Becomes 0
D. No effect
Answer: D
In a capacitor, Q is directly proportional to V. The constant of proportionality, in this case, is C, that is, the capacitance.
Capacitance is a constant so it will not change on changing voltage.
