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 

(1) 4 A

(2) 0.4 A

(3) 0.04 A

(4) 0.2 A

Subtopic:  Transformer |
 76%
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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 

(1) 200 V, 50 Hz

(2) 2 V, 50 Hz

(3) 200 V, 500 Hz

(4) 2 V, 5 Hz

Subtopic:  Transformer |
 81%
From NCERT
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A step-down transformer is connected to main supply 200V to operate a 6V, 30W bulb. The current in primary is 

(1) 3 A

(2) 1.5 A

(3) 0.3 A

(4) 0.15 A

Subtopic:  Transformer |
 77%
From NCERT
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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 

(1) 100

(2) 200

(3) 400

(4) 300

Subtopic:  Transformer |
 86%
From NCERT
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The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by V=5cosωt volts and I = 2 sin ωt amperes (where ω = 2πf). The power dissipated in the instrument is 

(1) Zero

(2) 10 W

(3) 5 W

(4) 2.5 W

Subtopic:  Different Types of AC Circuits |
 63%
From NCERT
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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 

(1) 60 Hz and 240 V

(2) 19 Hz and 120 V

(3) 19 Hz and 170 V

(4) 754 Hz and 70 V

Subtopic:  RMS & Average Values |
 80%
From NCERT
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The peak value of an alternating e.m.f. E is given by E=E0cosωt is 10 volts and its frequency is 50 Hz. At time t=1600sec, the instantaneous e.m.f. is

1. 10 V

2. 53V

3. 5 V

4. 1 V

Subtopic:  Different Types of AC Circuits |
 81%
From NCERT
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If a current I given by I0sinωtπ2 flows in an ac circuit across which an ac potential of E=E0sinωt has been applied, then the power consumption P in the circuit will be 

(1) P=E0I02

(2) P=2E0I0

(3) P=E0I02

(4) P = 0

Subtopic:  Different Types of AC Circuits |
 74%
From NCERT
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A resistance of \(20~ \mathrm{ohms}\) is connected to a source of an alternating potential, \(V=220sin(100 \pi t).\) The time taken by the current to change from its peak value to its r.m.s value will be: 

1. \( 0.2~ \mathrm{sec}\) 2. \( 0.25~ \mathrm{sec}\)
3. \(25 \times10^{-3}~ \mathrm{sec}\) 4. \(2.5 \times10^{-3}~ \mathrm{sec}\)
Subtopic:  RMS & Average Values |
 65%
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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 will be:

1. R + 2πfL

2. R2+4π2f2L2

3. R2+L2

4. R2+2πfL

Subtopic:  Different Types of AC Circuits |
 87%
From NCERT
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