A long solenoid has self-inductance L. If its length is doubled keeping total number of turns constant, then its new self-inductance will be:

1. $\frac{\mathrm{L}}{2}$

2. 2L

3. L

4. $\frac{\mathrm{L}}{4}$

A solenoid has 2000 turns wound over a length of 0.3 m. The area of its cross section is $1.2\times {10}^{-3} {\mathrm{m}}^2$. Around its central section of a coil of 300 turns is wound. If an initial current of 2A is reversed in 0.25 s, the e.m.f. induced in the coil is equal to

1. $6\times {10}^{-4} \mathrm{V}$

2. $4.8\times {10}^{-2} \mathrm{V}$

3. $2.4\times {10}^{-2} \mathrm{V}$

4. 48 kV

With the decrease of current in the primary coil from 2 A to zero in 0.01 s, the e.m.f. generated in the secondary coil is \(1000~\mathrm{V}\). The mutual inductance of the two coils is:

1. 1.25 H

2. 2.50 H

3. 5.00 H

4. 10.00 H

The coefficient of self induction of two inductor coils are 20 mH and 40 mH respectively. If the coils are connected in series so as to support each other and the resultant inductance is 80 mH then the value of mutual inductance between the coils will be:

1. 5 mH

2. 10 mH

3. 20 mH

4. 40 mH

A coil and a bulb are connected in series with a 12 volt direct current source. A soft iron core is now inserted in the coil. Then

1. The intensity of the bulb remains the same 

2. The intensity of the bulb decreases

3. The intensity of the bulb increases

4. Nothing can be said

A uniform magnetic field B is directed out of the page. A metallic wire has the shape of a square frame and is placed in the field as shown. While the shape of the wire is steadily transformed into a circle in the same plane, the current in the frame:

1. is directed clockwise

2. does not appear

3. is directed counter clockwise

4. is alternating

The dimension of the ratio of magnetic flux and the resistance is equal to that of:

1. induced emf

2. charge

3. inductance

4. current

Three identical coils A, B and C carrying currents are placed coaxially with their planes parallel to one another. A and C carry currents as shown. B is kept fixed, while A and C both are moved towards B with the same speed. Initially, B is equally seperated from A and C. The direction of the induced current in the coil B is :

1. same as that in coil A

2. same as that in coil B

3. zero

4. none of the above

In the arrangement shown in given figure, current from A to B is increasing in magnitude. Induced current in the loop will:

1. have clockwise direction

2. have anticlockwise direction

3. be zero

4. oscillate between clockwise and anticlockwise

Two identical coaxial circular loops carry a current \(i\) each circulating in the same direction. If the loops approach each other: