An alternating current is given as i = i1 cos ωt - i2 sin ωt. The rms current is given by

1.  i1 + i22 

2.  i1 + i22

3.  i12 + i222 

4.  I12 + i222

Concept Questions :-

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

1. 3.0 v

2. 0.75 v

3. 1.5 v

4. Zero

Concept Questions :-

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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. What is the current in the circuit :

1.  10A

2.  5A

3.  33.3A

4.  3.33A

 

Concept Questions :-

Different types of AC Circuits
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If XL = XC then the reading of  ideal voltmeter is: 

                             

1.  V = VL - VC 

2.  V = VR2 + VL2 

3.  V = VR2 + VL - VC2

4.  Zero

Concept Questions :-

LC oscillations
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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

Concept Questions :-

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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

Concept Questions :-

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In a LCR series network, VL=40 V, VC=20 V and VR=15 V. The supply voltage is

1.  25V

2.  75V

3.  35V

4.  Zero

Concept Questions :-

Different types of AC Circuits
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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

Concept Questions :-

LC oscillations
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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

Concept Questions :-

LC oscillations
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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%

Concept Questions :-

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