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

A transformer has 100 turns in the primary coil and carries 8 A current. If input power is one kilowatt, the number of turns required in the secondary coil to have 500V output will be 

(1) 100

(2) 200

(3) 400

(4) 300

A 220V input is supplied to a transformer.The output circuit draws a current of 2.0A at 440V. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is 

1. 3.6A                                        2. 2.8A

3. 2.5A                                        4. 5.0A

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. 100 mH

2. 1 mH

3. cannot be calculated unless R is known

4. 10 mH

A circuit when connected to an AC source of 12 V gives a current of 0.2 A. The same circuit when connected to a DC source of 12 V, gives a current of 0.4 A. The circuit is:

(1) series LR

(2) series RC

(3) series LC

(4) series LCR

The core of a transformer is laminated because:

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$\Omega$, the phase difference between the applied voltage and the current in the circuit is:

1.  $\frac{\mathrm{\pi }}{4}$

2.  $\frac{\mathrm{\pi }}{2}$

3.  zero

4.  $\frac{\mathrm{\pi }}{6}$

In the given circuit the reading of voltmeter V₁ and V₂ are 300 V each. The reading to the voltmeter V₃ and ammeter A are respectively:

1. 150 V, 2.2 A

2. 220 V, 2.2 A

3. 220 V, 2.0 A

4. 100 V, 2.0 A

An inductor 20 mH, a capacitor 100 μF, and a resistor 50 $\Omega$ are connected in series across a source of emf, V= 10sin314t. The power loss in the circuit is:

1. 0.79 W

2. 0.43 W

3. 2.74 W

4. 1.13 W

The potential differences across the resistance, capacitance and inductance are 80 V, 40 V and 100 V respectively in an L-C-R circuit. The power factor of this circuit is:

1.  0.4

2.  0.5

3.  0.8

4.  1.0