Alternating Current

In an ideal transformer, the turns ratio is NPNS = 12. The ratio VS : VP is equal to (the symbols carry their usual meaning) :

1. 1 : 2
2. 2 : 1
3. 1 : 1
4. 1 : 4

A 10 capacitor is connected to a 210 V, 50 Hz source as shown in figure. The peak current in the circuit is nearly ( = 3.14) : [figure]

1. 0.58 A
2. 0.93 A
3. 1.20 A
4. 0.35 A

In the circuit shown below, the inductance L is connected to an ac source. The current flowing in the circuit is I = I0 t. The voltage drop (VL) across L is [figure]

1. L I0 t
2. I0 L t
3. I0 L t
4. L I0 t

A step up transformer is connected to an ac mains supply of 220 V to operate at 11000 V, 88 watt. The current in the secondary circuit, ignoring the power loss in the transformer, is

1. 8 mA
2. 4 mA
3. 0.4 A
4. 4 A

The amplitude of the charge oscillating in a circuit decreases exponentially as Q = Q0e-Rt/2L, where Q0 is the charge at t = 0 s. The time at which charge amplitude decreases to 0.50Q0 is nearly: [Given that R = 1.5 , L = 12 mH, (2) = 0.693]

1. 19.01 ms
2. 11.09 ms
3. 19.01 s
4. 11.09 s

In a series LCR circuit, the inductance L is 10 mH, capacitance C is 1 and resistance R is 100 . The frequency at which resonance occurs is :-

1. 15.9 kHz
2. 1.59 rad/s
3. 1.59 kHz
4. 15.9 rad/s

A 12 V, 60 W lamp is connected to the secondary of a step down transformer, whose primary is connected to ac mains of 220 V. Assuming the transformer to be ideal, what is the current in the primary winding?

1. 2.7 A
2. 3.7 A
3. 0.37 A
4. 0.27 A

An ac source is connected to a capacitor C. Due to decrease in its operating frequency :

1. displacement current increases.
2. displacement current decreases.
3. capacitive reactance remains constant.
4. capacitive reactance decreases.

The net impedance of circuit (as shown in figure) will be : [figure]

1. 15
2. 5 5
3. 25
4. 10 2

The peak voltage of the ac source is equal to

1. The value of voltage supplied to the circuit
2. The rms value of the ac source
3. 2 times the rms value of the ac source
4. 1/ 2 times the rms value of the ac source