Physics - Alternating Current - Quiz-1

The core of a transformer is laminated to reduce energy losses due to

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Eddy currents
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Hysteresis
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Resistance in winding
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None of these

In the circuit given below, the reading of the voltmeter V will be:

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zero
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100 V
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200 V
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300 V

$An alternating current is given as i = i_{1} \cos ωt - i_{2} \sin ωt . The rms current is given by$

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$\frac{i_{1} + i_{2}}{\sqrt{2}}$
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$\frac{|i_{1} + i_{2}|}{\sqrt{2}}$
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$\sqrt{\frac{i_{1}^{2} + i_{2}^{2}}{2}}$
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$\sqrt{\frac{i_{1}^{2} + i_{2}^{2}}{\sqrt{2}}}$

In a step-up transformer, the turn ratio is 1:2. A Leclanche cell (e.m.f. 1.5V) is connected across the primary coil. The voltage developed in the secondary coil would be-

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3.0 V
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0.75 V
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1.5 V
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Zero

A 220 V, 50 Hz ac source is connected to an inductance of 0.2 H and a resistance of 20 ohms in series. What is the current in the circuit :

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10A
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5A
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33.3A
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3.33A

$If X_{L} = X_{C} then the reading of ideal voltmeter is :$

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$V = V_{L} - V_{C}$
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$V = \sqrt{V_{R}^{2} + V_{L}^{2}}$
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$V = \sqrt{V_{R}^{2} + {(V_{L} - V_{C})}^{2}}$
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Zero

An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is

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3Ω
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6Ω
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15Ω
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30Ω

A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be

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1600 A
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20 A
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4 A
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1.5 A

A loss free transformer has 500 turns on its primary winding and 2500 in secondary. The meters of the secondary indicate 200 volts at 8 amperes under these conditions. The voltage and current in the primary is

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100 V, 16 A
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40 V, 40 A
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160 V, 10 A
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80 V, 20 A

A transformer connected to 220 Volt line shows an output of 2 A at 11000 Volt. The efficiency is 100%. The current drawn from the line is:

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100 A
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200 A
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22 A
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11 A

A power transformer is used to step up an alternating e.m.f. of 220 V to 11 kV to transmit 4.4 kW of power. If the primary coil has 1000 turns, what is the current rating of the secondary ? Assume 100% efficiency for the transformer

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4 A
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0.4 A
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0.04 A
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0.2 A

The primary winding of transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an ac supply of 20 V, 50 Hz. The secondary will have an output of

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200 V, 50 Hz
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2 V, 50 Hz
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200 V, 500 Hz
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2 V, 5 Hz

A step-down transformer is connected to main supply 200V to operate a 6V, 30W bulb. The current in primary is

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3 A
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1.5 A
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0.3 A
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0.15 A

A transformer has 100 turns in the primary coil and carries 8 A current. If input power is one kilowatt, the number of turns required in the secondary coil to have 500V output will be

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100
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200
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400
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300

The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by $V = 5 \cos ω t$ volts and I = 2 sin ωt amperes (where ω = 2πf). The power dissipated in the instrument is

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Zero
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10 W
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5 W
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2.5 W

A generator produces a voltage that is given by V = 240 sin 120 t, where t is in seconds. The frequency and r.m.s. voltage are

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60 Hz and 240 V
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19 Hz and 120 V
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19 Hz and 170 V
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754 Hz and 70 V

The peak value of an alternating e.m.f. E is given by $E = E_{0} \cos ω t$ is 10 volts and its frequency is 50 Hz. At time $t = \frac{1}{600} s e c$ , the instantaneous e.m.f. is

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10 V
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$5 \sqrt{3} V$
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5 V
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1 V

If a current I given by $I_{0} \sin (ω t - \frac{π}{2})$ flows in an ac circuit across which an ac potential of $E = E_{0} \sin ω t$ has been applied, then the power consumption P in the circuit will be

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$P = \frac{E_{0} I_{0}}{\sqrt{2}}$

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$P = \sqrt{2} E_{0} I_{0}$

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$P = \frac{E_{0} I_{0}}{2}$

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P = 0

A resistance of 20 ohms is connected to a source of an alternating potential $V = 220 \sin (100 π t)$ . The time taken by the current to change from its peak value to r.m.s value is

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0.2 sec

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0.25 sec

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25 × 10^–3 sec

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2.5 × 10^–3 sec

An alternating current of frequency ‘f’ is flowing in a circuit containing a resistance R and a choke L in series. The impedance of this circuit is

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R + 2πfL

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$\sqrt{R^{2} + 4 π^{2} f^{2} L^{2}}$

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$\sqrt{R^{2} + L^{2}}$

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$\sqrt{R^{2} + 2 π f L}$

A resistance of 300 Ω and an inductance of $\frac{1}{π}$ henry are connected in series to a ac voltage of 20 volts and 200 Hz frequency. The phase angle between the voltage and current is :

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$\tan^{- 1} \frac{4}{3}$

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$\tan^{- 1} \frac{3}{4}$

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$\tan^{- 1} \frac{3}{2}$

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$\tan^{- 1} \frac{2}{5}$

In a region of uniform magnetic induction B = 10^–2 tesla, a circular coil of radius 30 cm and resistance π² ohm is rotated about an axis that is perpendicular to the direction of B and which forms a diameter of the coil. If the coil rotates at 200 rpm the amplitude of the alternating current induced in the coil is :

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4π² mA

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30 mA

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6 mA

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200 mA

In a LCR circuit having L = 8.0 henry, C = 0.5 μF and R = 100 ohm in series. The resonance frequency in radian per second is

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600 radian/second

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600 Hz

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500 radian/second

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500 Hz

The impedance of a circuit consists of 3 ohm resistance and 4 ohm reactance. The power factor of the circuit is :

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0.4

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0.6

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0.8

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1.0

The power factor of a good choke coil is:

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Nearly zero

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Exactly zero

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Nearly one

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Exactly one

L, C and R represent physical quantities inductance, capacitance and resistance respectively. The combination representing dimension of frequency is

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LC

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(LC)^–1/2

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${(\frac{L}{C})}^{- 1 / 2}$

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$\frac{C}{L}$

In an ac circuit, a resistance of R ohm is connected in series with an inductance L. If phase angle between voltage and current be 45°, the value of inductive reactance will be

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$\frac{R}{4}$

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$\frac{R}{2}$

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R

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Cannot be found with the given data

The phase difference between the current and voltage of LCR circuit in series combination at resonance is

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0

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π/2

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π

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–π

In a series resonant circuit, the ac voltage across resistance R, inductance L and capacitance C are 5 V, 10 V and 10 V respectively. The ac voltage applied to the circuit will be

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20 V

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10 V

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5 V

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25 V

In a series LCR circuit, resistance R = 10Ω and the impedance Z = 20Ω. The phase difference between the current and the voltage is

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30°

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45°

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60°

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90°

0:0:1

0:0:1

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