10 QA on alternating current

10 QA on alternating current | Learn Physics

10 Question-Answer on alternating current

1. A voltmeter reads V volt in an A.C. circuit. Then V is:

(a) Peak value of voltage

(b) Peak value of current

(d) R.m.s. value of voltage.

Ans: ( d)

2. If an alternating current of frequency 50 Hz is flowing through a conducting wire; then how many times does the current become zero in one second?

(a) 125 times

(b) 100 times

(d) 25 times

Ans: (b)

3. A coil has an inductance of 0.7 henry and is joined in series with a resistance of 220Ω. When an alternating e.m.f. of 220 V at 50 cycles per second, is applied to it, then wattles component of current in the circuit is:

(a) 7 A

(b) 5 A

(d) 0.5 A.

Ans: ( c)

4. In L-R circuit, the A.C. source has voltage 220V. if potential difference across inductance is 176 V, the potential difference across the resistance will:

(a) 44 V

(b) 110 V

(d) 220 V

Ans: (a)

5. When the frequency of A.C. is doubled, the impedance of an R-C circuit

(a) Is doubled

(b) Is halved

(d) Decreases

Ans: ( d)

6. When the frequency of A.C. is doubled, the impedance of an L-C-R circuit

(a) Is halved

(b) Is doubled

(d) Decreases

Ans: (c)

7. In an A.C. circuit, resistance, inductance and capacitance are connected in series. The value of potential differences across three is 70 halved, 90 halved and 65 V respectively. The value of potential difference of A.C. source is:

(a) 225 V

(b) 95 V

(d) 74.3 V

Ans: ( d)

8. An a.c. series circuit contains 8 ohm of resistance and 6 ohm of inductive reactance. What is the impedance of the circuit?

(a) 14 ohm

(b) 2 ohm

(d) 14.2 ohm

Ans: ( c)

9. With increase in frequency of an a.c. supply, the capacitative reactance

(a) Varies inversely with frequency

(b) Varies directly with frequency

(d) Remains constant

Ans: ( a)

10. A 20 volt a.c. is applied to a circuit consisting of a resistance and a coil with negligible resistance. If the voltage across the resistance is 12 volt, the voltage across the coil is:

(a) 16 volt

(b) 10 volt

(d) 6 volt

Ans: (a)

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