One conducting U tube can slide inside another as shown in figure, maintaining electrical contacts between the tubes. The magnetic field B is perpendicular to the plane of the figure. If each tube moves towards the other at a constant speed v then the emf induced in the circuit in terms of B, l and v where l is the width of each tube, will be 

1. Zero

2. 2 Blv

3. Blv

4. – Blv

The magnitude of the earth’s magnetic field at a place is B₀ and the angle of dip is δ. A horizontal conductor of length l lying along the magnetic north-south moves eastwards with a velocity v. The emf induced across the conductor is 

1. Zero

2. B₀lv sinδ

3. B₀lv

4. B₀lv cosδ

Two circuits have coefficient of mutual induction of 0.09 henry. Average e.m.f. induced in the secondary by a change of current from 0 to 20 ampere in 0.006 second in the primary will be 

1. 120 V

2. 80 V

3. 200 V

4. 300 V

A coil and a bulb are connected in series with a dc source, a soft iron core is then inserted in the coil. Then 

1. Intensity of the bulb remains the same

2. Intensity of the bulb decreases

3. Intensity of the bulb increases

4. The bulb ceases to glow

The inductance of a coil is 60μH. A current in this coil increases from 1.0 A to 1.5 A in 0.1 second. The magnitude of the induced e.m.f. is 

1. 60 × 10^–6 V

2. 300 × 10^–4 V

3. 30 × 10^–4 V

4. 3 × 10^–4 V

The self inductance of a coil is L. Keeping the length and area same, the number of turns in the coil is increased to four times. The self inductance of the coil will now be 

1. $\frac{1}{4}L$

2. L

3. 4 L

4. 16 L

A coil has an inductance of 2.5 H and a resistance of 0.5 r. If the coil is suddenly connected across a 6.0 volt battery, then the time required for the current to rise 0.63 of its final value is 

1. 3.5 sec

2. 4.0 sec

3. 4.5 sec

4. 5.0 sec

Pure inductance of 3.0 H is connected as shown below. The equivalent inductance of the circuit is

1. 1 H

2. 2 H

3. 3 H

4. 9 H

If a current of 10 A flows in one second through a coil, and the induced e.m.f. is 10 V, then the self-inductance of the coil is 

1. $\frac{2}{5}H$

2. $\frac{4}{5}H$

3. $\frac{5}{4}H$

4. 1 H

The adjoining figure shows two bulbs \(B_1\) and \(B_2\) resistor \(R\) and an inductor \(L\). When the switch \(S\) is turned off