1. What is the SI unit of capacitive reactance?
A.
Ohm
B.
Farad
C.
Henry
D.
Volt
Correct Answer:
Ohm
Explanation:
Capacitive reactance represents opposition to alternating current and is measured in ohms (Ω).
2. The capacitive reactance of a capacitor is given by which expression?
A.
Xc = 2πfC
B.
Xc = 1/(2πfC)
C.
Xc = 2πC/f
D.
Xc = f/(2πC)
Correct Answer:
Xc = 1/(2πfC)
Explanation:
The capacitive reactance is Xc = 1/(2πfC), where f is frequency and C is capacitance.
3. What happens to the capacitive reactance when the frequency of the AC supply is increased?
A.
It increases
B.
It decreases
C.
It becomes zero for every frequency
D.
It remains unchanged
Correct Answer:
It decreases
Explanation:
Since Xc = 1/(2πfC), capacitive reactance is inversely proportional to frequency.
4. What happens to the capacitive reactance when the capacitance is doubled, while frequency remains constant?
A.
It doubles
B.
It becomes four times
C.
It becomes half
D.
It remains unchanged
Correct Answer:
It becomes half
Explanation:
Capacitive reactance is inversely proportional to capacitance, so doubling C reduces Xc to half its original value.
5. A capacitor of capacitance 1 F is connected to an AC source of frequency 1/(2π) Hz. What is its capacitive reactance?
A.
0.5 ohm
B.
1 ohm
C.
2 ohms
D.
2π ohms
Correct Answer:
1 ohm
Explanation:
Using Xc = 1/(2πfC), Xc = 1/[2π × 1/(2π) × 1] = 1 ohm.
6. A capacitor has a capacitive reactance of 10 ohms at a certain frequency. If the frequency is doubled, what is its new reactance?
A.
5 ohms
B.
10 ohms
C.
20 ohms
D.
40 ohms
Correct Answer:
5 ohms
Explanation:
Because capacitive reactance is inversely proportional to frequency, doubling the frequency halves the reactance from 10 ohms to 5 ohms.
7. For a fixed frequency, which capacitor has the greatest capacitive reactance?
A.
A 1 microfarad capacitor
B.
A 2 microfarad capacitor
C.
A 5 microfarad capacitor
D.
A 10 microfarad capacitor
Correct Answer:
A 1 microfarad capacitor
Explanation:
At fixed frequency, Xc is inversely proportional to capacitance. Therefore, the smallest capacitance has the greatest reactance.
8. A capacitor has a capacitive reactance of 20 ohms at 50 Hz. What will its reactance be at 100 Hz?
A.
5 ohms
B.
10 ohms
C.
20 ohms
D.
40 ohms
Correct Answer:
10 ohms
Explanation:
The frequency doubles from 50 Hz to 100 Hz, so the capacitive reactance becomes half: 20/2 = 10 ohms.
9. If the capacitance of a capacitor increases, its capacitive reactance will:
A.
Increase
B.
Decrease
C.
First increase and then decrease
D.
Become independent of frequency
Correct Answer:
Decrease
Explanation:
From Xc = 1/(2πfC), capacitive reactance decreases as capacitance increases.
10. At very high frequency, the capacitive reactance of a capacitor becomes:
A.
Very large
B.
Very small
C.
Equal to its capacitance
D.
Independent of frequency
Correct Answer:
Very small
Explanation:
Since Xc is inversely proportional to frequency, its value becomes very small at very high frequency.
Short questions are currently unavailable for this page.