Alternating current cannot be measured by a D.C. ammeter because:

1. A.C. cannot pass through D.C. Ammeter
2. A. C. changes direction
3. Average value of current for the complete cycle is zero
4. D.C. Ammeter will get damaged

Subtopic:  AC vs DC |
 64%
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In an L-R circuit, the inductive reactance is equal to the resistance R of the circuit. An emf of E = E0cos(ωt) is applied to the circuit. The power consumed by the circuit is:

1. E022R

2. E024R

3. E022R

4. E028R

Subtopic:  Power factor |
 53%
From NCERT
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A series AC circuit has a resistance of 4 Ω and an inductor of reactance 3 Ω. The impedance of the circuit is z1. Now when a capacitor of reactance 6 Ω is connected in series with the above combination, the impedance becomes z2. z1z2 will be:

1. 1 : 1

2. 5 : 4

3. 4 : 5

4. 2 : 1

Subtopic:  Different Types of AC Circuits |
 86%
From NCERT
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An inductor (L) and resistance (R) are connected in series with  an AC source. The phase difference between voltage (V) and current (i) is 45°. If the phase difference between V and i remains the same, then the capacitive reactance and impedance of the L-C-R circuit will be:

1. 2R, R2

2. R, R2

3. R, R

4. 2R, R3

Subtopic:  Different Types of AC Circuits |
 54%
From NCERT
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What is the value of inductance L for which the current is a maximum in a series LCR circuit with C=10 μF and ω = 1000 s-1?

1. 10 mH
2. 100 mH
3. 1 mH
4. Cannot be calculated unless R is known

Subtopic:  Different Types of AC Circuits |
 77%
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A 50 Hz a.c. source of 20 volts is connected across R and C as shown in the figure below. If the voltage across R is 12 volts, then the voltage across C will be:
   

1. 8 V
2. 16 V
3. 10 V
4. not possible to determine unless values of R and C are given

Subtopic:  Different Types of AC Circuits |
 72%
From NCERT
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A transformer has an efficiency of 90% when working on a 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the secondary coil and the current in the primary coil, respectively, are:

1. 300 V, 15 A

2. 450 V, 15 A

3. 450 V, 13.5 A

4. 600 V, 15 A

Subtopic:  Transformer |
 74%
From NCERT
AIPMT - 2014
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The core of a transformer is laminated because:

1. Energy losses due to eddy currents may be minimized
2. The weight of the transformer may be reduced
3. Rusting of the core may be prevented
4. Ratio of voltage in primary and secondary may be increased
Subtopic:  Transformer |
 90%
From NCERT
AIPMT - 2006
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How much power is dissipated in an \(\mathrm{L-C-R}\) series circuit connected to an \(\mathrm{AC}\) source of emf \(\mathrm E\)?

1. \(\frac{\varepsilon^{2} R}{\left[R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}\right]}\) 2. \(\frac{\varepsilon^{2} \sqrt{R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}}}{R}\)
3. \(\frac{\varepsilon^{2}\left[R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}\right]}{R}\) 4. \(\frac{\varepsilon^{2}R}{\sqrt{R^{2}+\left(L \omega-\frac{1}{C \omega}\right)^{2}}}\)
Subtopic:  Power factor |
 71%
From NCERT
AIPMT - 2009
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A coil of inductive reactance of 31 Ω has a resistance of 8 Ω. It is placed in series with a condenser of capacitive reactance 25 Ω. The combination is connected to an a.c. source of 110 V. The power factor of the circuit is:

1. 0.56

2. 0.64

3. 0.80

4. 0.33

Subtopic:  Power factor |
 84%
From NCERT
AIPMT - 2006
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