Alternating Current

The core of a transformer is laminated because

1. ratio of voltage in primary and secondary may be increased
2. energy losses due to eddy currents may be minimised
3. the weight of the transformer may be reduced
4. rusting of the core may be prevented.

A transistor-oscillator using a resonant circuit with an inductor L (of negligible resistance) and a capacitor C in series produces oscillations of frequency f. If L is doubled and C is changed to 4C, the frequency will be

1. f/2
2. f/4
3. 8f
4. f/2 2

In a circuit L, C and R are connected in series with an alternating voltage source of frequency f. The current leads the voltage by 45 . The value of C is

1. 1 f(2 fL - R)
2. 12 f(2 fL - R)
3. 1 f(2 fL + R)
4. 12 f(2 fL + R)

For a series LCR circuit the power loss at resonance is

1. V2 [ L - 1 C ]
2. I2L
3. I2R
4. V2C

A capacitor of capacity C has reactance X. If capacitance and frequency become double then reactance will be

1. 4X
2. X/2
3. X/4
4. 2X

The value of quality factor is

1. LR
2. 1 RC
3. LC
4. L/R