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CBSE

Subject

Physics

NEET Physics : Alternating Current

Multiple Choice Questions

31.

In a circuit, L, C and R are connected in series with an alternating voltage source of frequency f. The current leads the voltage by 45°. The value of C is

$\frac{1}{2 πf (2 πf L + R)}$
$\frac{1}{πf (2 πf L + R)}$
$\frac{1}{2 πf (2 πf L - R)}$
$\frac{1}{πf (2 πf L - R)}$

32.

In a series L-C-R circuit, resistance R = 10 Ω and the impedance Z = 10 Ω. The phase difference between the current and the voltage is

0^o
30^o
45^o
60^o

33.

The impedance of a circuit, when a resistance R and an inductor of inductance L are connected in series in an AC circuit of frequency f, is

$\sqrt{R + 2 π^{2} f^{2} L^{2}}$
$\sqrt{R + 4 π^{2} f^{2} L^{2}}$
$\sqrt{R^{2} + 4 π^{2} f^{2} L^{2}}$
$\sqrt{R^{2} + 2 π^{2} f^{2} L^{2}}$

34.

A choke is preferred to a resistance for limiting current in AC circuit because

choke is cheap
there is no wastage of power
choke is compact in size
choke is a good absorber of heat

35.

Induced emf in the coil depends upon

conductivity of coil
amount of flux
rate of change of linked flux
resistance of coil

36.

In an L-C-R circuit inductance is changed from L to L/2.To keep the same resonance frequency, C should be changed to

2 C
$\frac{C}{2}$
4 C
$\frac{C}{4}$

37.

220 V, 50 Hz, AC source is connected to an inductance of 0.2 Hand a resistance of 20 Ω in series. Whatis the current in the circuit?

3.33 A
33.3 A
5 A
10 A

38.

If we change the value of R, then

voltage does not change on L
voltage does not change on LC combination
voltage does not change on C
voltage changes on LC combination

39.

Real power consumption in a circuit is least when it contains.

high R, low L
high R, high L
low R, high L
high R, low C

40.

The rms speed (in m/s) of oxygen molecules of the gas at temperature 300 K, is

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