A wire of fixed lengths is wound on a solenoid of length l and radius r. Its self inductance is found to be L. Now if same wire is wound on a solenoid of length l/2 and radius r/2, then the self inductance will be –

1.  2L                     

2.  L 

3.  4L                     

4.  8L

Concept Questions :-

Self-inductance
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A wire in the form of a circular loop of radius 10 cm lies in a plane normal to a magnetic field of 100 T. If this wire is pulled to take a square shape in the same plane in 0.1 s, average induced emf in the loop is: 

1.  6.70 volt                   

2.  5.80 volt 

3.  6.75 volt                   

4.  5.75 volt

Concept Questions :-

Faraday 's law and lenz law
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A superconducting loop of radius R has self inductance L. A uniform and constant magnetic field B is applied perpendicular to the plane of the loop. Initially current in this loop is zero. The loop is rotated by 180°. The current in the loop after rotation is equal to –

1. zero                                 

2. BπR2L

3. 2BπR2L                           

4. BπR22L

Concept Questions :-

Self-inductance
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A coil of inductance 8.4 mH and resistance 6Ω is connected to a 12 V battery. The current in the coil is 1.0 A at approximately the time. 

1.  500 ms                 

2.  20 ms 

3.  35 ms                   

4.  1 ms

Concept Questions :-

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PQ is an infinite current carrying conductor. AB and CD are smooth conducting rods on which a conductor EF moves with constant velocity V as shown. The force needed to maintain constant speed of EF is –

                    

1. 1VRμ0IV2π ln ba2                       

2. 1VRμ0IV2 ln ba2

3. VRμ0IV2 ln ba2                         

4. VRμ0IV2π ln ba2

Concept Questions :-

Motional emf
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A 50 turns circular coil has a radius of 3 cms, it is kept in a magnetic field acting normal to the area of the coil. The magnetic field B increased from 0.10 tesla to 0.35 tesla in 2 milliseconds. The average induced emf in the coil is-

1.  1.77 volts                     

2.  17.7 volts 

3.  177 volts                     

4.  0.177 volts

Concept Questions :-

Faraday 's law and lenz law
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A semicircular wire of radius R is rotated with constant angular velocity ω about an axis passing through one end and perpendicular to the plane of the wire.

                         

There is a uniform magnetic field of strength B. The induced emf between the ends is -

1. BωR2/2                           

2. 2BωR2

3. is variable                         

4. none of these

Concept Questions :-

Motional emf
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The inductance of a closed-packed coil of 400 turns is 8 mH. A current of 5 mA is passed through it. The magnetic flux through the coil is approximately

1.  0.1 μ0 Wb                     

2.  0.2 μ0 Wb

3.  1.0 μ0 Wb                     

4.  2.0 μ0 Wb

Concept Questions :-

Self-inductance
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Loop A of radius (r << R) moves towards loop B with a constant velocity v in such a way that their planes are always parallel.

                       

What is the distance (x) between the two loops when the induced emf in loop A is maximum –

1. R                                     

2. R2

3. R2                                     

4. R1-12

Concept Questions :-

Motional emf
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The current in an L – R circuit builds up to 3/4th of its steady state value in 4 seconds. The time constant of this circuit is

1. 1In 2sec                       

2. 2In 2sec

3. 3In 2sec                       

4. 4In 2sec

Concept Questions :-

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