Free Printable Alternating current (01)

1.

Alternating current is transmitted to distant places

a)

At high voltage and Low current

b)

At high voltage and high current

c)

At low voltage and low current

d)

At low voltage and high current

2.

220 V, 50 Hz AC is applied to a resistor. The instantaneous value of value is

a)

$220\ \sqrt{2}\sin\ 100\pi t$

b)

$220\ \sin100\pi t$

c)

$220\sqrt{2}\sin50\pi t$

d)

$220\sin50\pi t$

3.

If the rms current in a 50 Hz AC circuit is 5 A, the value of the current 1/300 s after its value becomes zero is

a)

$5\sqrt{2\ }A$

b)

$5\sqrt{\frac{3}{2}}A$

c)

$\frac{5}{6}A$

d)

$\frac{5}{\sqrt{2}}A$

4.

An alternating current of rms value 10 A is passed through a 12 $\Omega$ resistor.The maximum Potential difference across the resistor is

a)

20 V

b)

90 V

c)

169.7 V

d)

None of these

5.

Same current is flowing in two alternating circuits. The first circuit contains only inductance and the other contains only a capacitor. If the frequency of the emf of AC is increased, the effect on the value of the current

a)

Increases in the first circuit and decreases in the other

b)

Increases in both the circuits

c)

Decreases in both the circuits

d)

Decreases in the first circuit and increases in the other.

6.

An inductance and resistance are connected in series with an AC potential. In this circuit

a)

The current and the potential difference across the resistance lead the Potential Difference across the inductance by phase angle $\frac{\pi}{2}$

b)

The current and the potential difference across the resistance lag behind potential difference across the inductance by an angle $\frac{\pi}{2}$

c)

The current and the potential difference across the resistance lag behind the potential difference across the inductance by an angle $\pi$

d)

The potential difference across the resistance lags behind the potential difference across the inductance by an angle $\frac{\pi}{2}$ but the current in the resistance leads the potential difference across inductance by $\frac{\pi}{2}$

7.

An AC voltage is applied to a resistance R and an inductor L in series. If R and the inductive reactance are both equal to 3 $\Omega$ ,the phase difference (in rad) between the applied voltage and the current in the circuit is

a)

$\frac{\pi}{4}$

b)

$\frac{\pi}{2}$

c)

zero

d)

$\frac{\pi}{6}$

8.

In a circuit containing R and L as the frequency of the impressed AC increases, the impedance of the circuit

a)

Decreases

b)

increases

c)

remains unchanged

d)

First increases and then decreases

9.

When an AC voltage is applied to an LCR circuit, then

a)

I and V are out of phase with each other in R

b)

I and V are in phase in L with in C, they are out of phase

c)

I and V are out of phase in both C and L

d)

I and V are out of phase in L and in phase in C

10.

An LCR series circuit, connected to a source $\epsilon$ , is at resonance. Then,

a)

The voltage across R is zero

b)

The voltage across R equals applied voltage

c)

The voltage across C is zero

d)

The voltage across C equals applied voltage

11.

A sinusoidal voltage of peak value 300 V and an angular frequency $\omega\ =400\ rads^{-1}$ is applied to series LCR circuit, in which R = 3 ohm, L= 20 mH and C = 625 microFarad. The peak current in the circuit is

a)

$30\sqrt{2}A$

b)

60 A

c)

100 A

d)

$60\sqrt{2}A$

12.

In an LCR circuit if impedance is $\sqrt{2}$ times of resistance, then the phase difference is

a)

zero

b)

$30^0$

c)

$60^0$

d)

$45^0$

13.

In an LCR series AC circuit, if $\omega_o$ is the resonant angular frequency, then the quality factor is given by

a)

$\frac{\omega_oL}{C}$

b)

$\left(\frac{1}{R}\right)\sqrt{\frac{L}{C}}$

c)

$\frac{\omega_oC}{R}$

d)

$\frac{L}{\omega_oR}$

14.

110 $V_{rms}$ is applied across a series circuit having resistance 11 ohm and impedance 22 ohm. The power consumed is

a)

275 W

b)

366 W

c)

550 W

d)

1100 Wi

15.

AC generator is used to

a)

Convert low voltage into high voltage

b)

high voltage into low voltage

c)

mechanical energy into electrical energy

d)

All of the above

16.

The selectivity of a series LCR AC circuit is large, when

a)

L is large and R is large

b)

L is small and R is small

c)

L is large and R is small

d)

L = R

17.

The core of a transformer is laminated because

a)

Energy losses due to eddy currents may be minimised

b)

The weight of the transformer may be reduced

c)

rusting of the core may be prevented

d)

Ratio of voltages in primary and secondary may be increased

18.

The transformation ratio (k = $\frac{Vs}{Vp}$ ) in the step-up transformer is

a)

one

b)

greater than one

c)

less than one

d)

the ratio greater or less than one depends on the other factors

19.

When the frequency of an AC circuit is doubled, then the capacitive reactance will be...........

a)

Halved

b)

Doubled

c)

Squared

d)

Tripled

20.

In an LCR circuit, capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to .......

a)

4 L

b)

2 L

c)

L/2

d)

L/ 4

Alternating current (01)

Total questions: 20

Worksheet time: 1hrs 24mins

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