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 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 B₁ and B₂ resistor R and an inductor L. When the switch S is turned off 

1. Both B₁ and B₂ die out promptly

2. Both B₁ and B₂ die out with some delay

3. B₁ dies out promptly but B₂ with some delay

4. B₂ dies out promptly but B₁ with some delay

An inductance L and a resistance R are first connected to a battery. After some time the battery is disconnected but L and R remain connected in a closed circuit. Then the current reduces to 37% of its initial value in time ?

(1) RL sec

(2) $\frac{R}{L}sec$

(3) $\frac{L}{R}sec$

(4) $\frac{1}{LR}sec$