# NCERT Physics Class 12 Exemplar Ch 6 Electromagnetic Inductions Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q 26. A rectangular loop of wire ABCD is kept close to an infinitely long wire carrying a current for and Find the total charge passing through a given point in the loop, in time T. The resistance of the loop is R.

If is the current in the loop.

If Q is the charge that passed in time t,

Integrating

The magnitude of change is

Q. 27 A magnetic field B is confined to a region and points out of the paper (the z-axis) , being the centre of the circular region. A charged ring (charge ) of radius and mass m lies in the plane with its centre at the origin. The ring is free to rotate and is at rest. The magnetic field is brought to zero in time . Find the angular velocity of the ring after the field vanishes.

Ans:

Torque

If is the change in angular momentum

Initial angular momentum

Final angular momentum

Q 28. A rod of mass m and resistance R slides smoothly over two parallel perfectly conducting wires kept sloping at an angle with respect to the horizontal. The circuit is closed through a perfect conductor at the top. There is a constant magnetic field B along the vertical direction. If the rod is initially at rest, find the velocity of the rod as a function of time.

Ans:

(A is a constant to be determine by initial conditions)

Q 29. Find the current in the sliding rod AB (resistance = R) for the arrangement shown in. B is constant and is out of the paper. Parallel wires have no resistance. v is constant. Switch S is closed at time .

Ans:

If Q (t) is charge on the capacitor (note current flows from A to B)

. Differentiating, we get