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

(c)    R.m.s. 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

(c)    75 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

(c)    0.7 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

(c)    132 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

(c)    Increases

(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

(c)    Increases

(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

(c)    85 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

(c)    10 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

(c)    Varies directly as square of 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

(c)    8 volt

(d)   6 volt

Ans: (a)