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 coils of self inductance L₁ and L₂ are placed closer to each other so that total flux in one coil is completely linked with other. If M is mutual inductance between them, then 

(1) M = L₁ L₂

(2) M = L₁/L₂

(3) $M=\sqrt{L_1{L}_2}$

(4) M = (L₁ L₂)²

Two circuits have coefficient of mutual induction of \(0.09\) henry. Average emf 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

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

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

In the figure magnetic energy stored in the coil is:

An electric motor operating on a 60 V dc supply draws a current of 10 A. If the efficiency of the motor is 50%, the resistance of its winding is 

(1) 3Ω

(2) 6Ω

(3) 15Ω

(4) 30Ω