A step-down transformer is employed to reduce the main supply of AC from 220V to 11V. If the primary coil draws a current of 5A and the secondary supplies a current of 90A, then the efficiency of the transformer is  -

1.  10%

2.  95%

3.  90%

4.  80%

Subtopic:  Transformer |
 84%
From NCERT
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At resonance, the value of the power factor of the circuit is -

1.  1

2.  Zero

3.  Between zero and 1

4.  More than 1

Subtopic:  LC Oscillations (OLD NCERT) |
 81%
From NCERT
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In a LCR circuit having L = 8.0 henry, C = 0.5 μF and R = 100 Ω in series, the resonance frequency (in Hz) is 

1.  250πHz  

2.  600πHz  

3.  500πHz 

4.  500 Hz

Subtopic:  LC Oscillations (OLD NCERT) |
 81%
From NCERT
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In an LCR series network, VL=40 V, VC=20 V and VR=15 V. The supply voltage will be:

1.  25 V

2.  75 V

3.  35 V

4.  Zero

Subtopic:  Different Types of AC Circuits |
 88%
From NCERT
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The ratio of the number of turns in secondary to primary in an ideal transformer varies from 50 to 550. If the power input is P, then its output power is  -

1.  11P

2.  P11

3.  18P111

4.  P

Subtopic:  Transformer |
From NCERT
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Loss in energy in the transformer is due to 

1.  Hysteresis

2.  Eddy current loss

3.  Leakage of flux

4.  All of these

Subtopic:  Transformer |
 88%
From NCERT
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An alternating current is given as i = icos \(\omega t\) - isin \(\omega t\). The value of rms current is given by:
1. \( \frac{1}{\sqrt{2}}\left(i_1+i_2\right) \)
2. \( \frac{1}{\sqrt{2}}\left(i_i+i_2\right)^2 \)
3. \( \frac{1}{\sqrt{2}}\left(i_1^2+i_2^2\right)^{1 / 2} \)
4. \( \frac{1}{2}\left(i_1^2+i_2^2\right)^{1 / 2}\)

Subtopic:  RMS & Average Values |
 80%
From NCERT
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In a step-up transformer, the turn ratio is 1:2 . A Leclanche cell (e.m.f. 1.5 V) is connected across the primary coil. What would be the voltage developed in the secondary coil?

1. 3.0 V 2. 0.75 V
3. 1.5 V 4. Zero
Subtopic:  Transformer |
From NCERT
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A 220 V, 50 Hz ac source is connected to an inductance of 0.2 H and a resistance of 20 ohms in series. How much current flows across the circuit?

1.  10 A

2.  5 A

3.  33.3 A

4.  3.33 A

Subtopic:  Different Types of AC Circuits |
 64%
From NCERT
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When a step-down transformer is connected to a 2400 volt line, the output load receives 80 amps of current. The ratio of the turns in the primary and secondary coils is 20:1. If transformer efficiency is 100%, then the current flowing in the primary coil will be:

1. 1600 A 2. 20 A
3. 4 A 4. 1.5 A
Subtopic:  Transformer |
 76%
From NCERT
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