It is desired to measure the magnitude of the field between the poles of a powerful loudspeaker magnet. A small flat search coil of area $2 c{m}^2$ with 25 closely wound turns, is positioned normal to the field direction, and then quickly snatched out of the field region. Equivalently, one can give it a quick 90° turn to bring its plane parallel to the field direction). The total charge flown in the coil (measured by a ballistic galvanometer connected to the coil) is 7.5 mC. The combined resistance of the coil and the galvanometer is 0.50 $\Omega$. The field strength of the magnet is:

1. 0.55 T
2. 0.75 T
3. 0.67 T
4. 0.49 T

What is the dimensional formula of magnetic flux?

1. $[\mathrm{M}$ ${\mathrm{L}}^2$ ${\mathrm{T}}^{-2}$ ${\mathrm{A}}^{-1}]$

2. $[\mathrm{M}$ ${\mathrm{L}}^1$ ${\mathrm{T}}^{-1}$ ${\mathrm{A}}^{-2}]$

3. $[\mathrm{M}$ ${\mathrm{L}}^2$ ${\mathrm{T}}^{-3}$ ${\mathrm{A}}^{-1}]$

4. $[\mathrm{M}$ ${\mathrm{L}}^{-2}$ ${\mathrm{T}}^{-2}$ ${\mathrm{A}}^{-2}]$

A cylindrical magnet is kept along the axis of a circular coil. On rotating the magnet about its axis, the coil will have induced in it:

A bar magnet is made to fall through a long surface copper tube. The speed (v) of the magnet as a function of time (t) is best represented by:

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

Figure shows a metal rod PQ resting on the smooth rails AB and positioned between the poles of a permanent magnet. The rails, the rod, and the magnetic field are in three mutually perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod = 15 cm, B = 0.50 T, resistance of the closed-loop containing the rod = 9.0 mΩ. Assume the field to be uniform.

What is the emf induced in the moving rod if the direction of the magnetic field is changed from perpendicular to parallel to the rails?

1. 0
2. 9 mV
3. 0.9 mV
4. None of these