Alternating Current

To an ac power supply of 220 V at 50 Hz, a resistor of 20 , a capacitor of reactance 25 and an inductor of reactance 45 are connected in series. The corresponding current in the circuit and the phase angle between the current and the voltage is, respectively

1. 15.6 A and 30
2. 15.6 A and 45
3. 7.8 A and 30
4. 7.8 A and 45

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