Alternating Current · Question 30

A transformer having efficiency of 90% is working on 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

A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when

1. a capacitance of reactance XC = XL is included in the same circuit.
2. an iron rod is inserted in the coil.
3. frequency of the AC source is decreased.
4. number of turns in the coil is reduced.

The primary of a transformer when connected to a dc battery of 10 Volt draws a current of 1 mA. The number of turns of the primary and secondary windings are 50 and 100 respectively. The voltage in the secondary and the current drawn by the circuit in the secondary are respectively

1. 20 V and 2.0 mA
2. 10 V and 0.5 mA
3. Zero volt and therefore no current
4. 20 V and 0.5 mA

The instantaneous values of alternating current and voltage in a circuit are given as i = 1 2 (100 t) ampere e = 1 2 (100 t + 3 ) Volt The average power in watts consumed in the circuit is

1. 14
2. 34
3. 12
4. 18

In an electrical circuit R, L, C and a.c. voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and the current in the circuit is 3. If instead, C is removed from the circuit, the phase difference is again 3. The power factor of the circuit is

1. 12
2. 1 2
3. 1
4. 32

The r.m.s. value of potential difference V shown in the figure is [figure]

1. V0 3
2. V0
3. V0 2
4. V02

A coil has resistance 30 ohm and inductive reactance 20 ohm at 50 Hz frequency. If an ac source, of 200 volt, 100 Hz, is connected across the coil, the current in the coil will be

1. 2.0 A
2. 4.0 A
3. 8.0 A
4. 20 13 A

An ac voltage is applied to a resistance R and an inductor L in series. If R and the inductive reactance are both equal to 3 Ω, the phase difference between the applied voltage and the current in the circuit is

1. /6
2. /4
3. /2
4. zero

In the ac circuit an alternating voltage e = 200 2 sin 100t volts is connected to a capacitor of capacity 1 . The r.m.s. value of the current in the circuit is

1. 10 mA
2. 100 mA
3. 200 mA
4. 20 mA

A condenser of capacity C is charged to a potential difference of V1. The plates of the condenser are then connected to an ideal inductor of inductance L. The current through the inductor when the potential difference across the condenser reduces to V2 is

1. ( C(V1-V2)2L ) 12
2. C (V12-V22 )L
3. C (V12+V22 )L
4. ( C (V12-V22 )L ) 12