Chapter 6: Electromagnetic Induction

A square of side L meters lies in the x-y plane in a region, where the magnetic field is given by B = Bo (2i + 3j + 4k) T where Bo is constant. The magnitude of flux passing through the square is

(a) 2 Bo L² Wb.

(b) 3 Bo L² Wb.

(c) 4 Bo L² Wb.

(d) √29 B Lo² Wb

A loop, made of straight edges has six corners at A(0,0,0), B(L,O,0) C(L,L,0), D(0,L,0) E(0,L,L) and F(0,0,L). A magnetic field B = Bo (i + k)T is present in the region. The flux passing through the loop ABCDEFA (in that order) is

(a) Bo L² Wb.

(b) 2 Bo L² Wb.

(c) 2 Bo L² Wb.

(d) 4 Bo L² Wb.

A cylindrical bar magnet is rotated about its axis. A wire is connected from the axis and is made to touch the cylindrical surface through a contact. Then

(a) a direct current flows in the ammeter A.

(b) no current flows through the ammeter A.

(c) an alternating sinusoidal current flows through the ammeter A with a time period T=2π/ω.

(d) a time-varying non-sinusoidal current flows through the ammeter A.

There are two coils A and B. A current starts flowing in B as shown, when A is moved towards B and stops when A stops moving. The current in A is counterclockwise. B is kept stationary when A moves. We can infer that

(a) there is a constant current in the clockwise direction in A.

(b) there is a varying current in A.

(c) there is no current in A.

(d) there is a constant current in the counterclockwise direction in A.

Same as problem 4 except the coil A is made to rotate about a vertical axis. No current flows in B if A is at rest. The current in coil A, when the current in B (at t = 0) is counterclockwise and the coil A is as shown at this instant, t = 0, is

(a) constant current clockwise.

(b) varying current clockwise.

(c) varying current counterclockwise.

(d) constant current counterclockwise.

The self-inductance L of a solenoid of length l and area of cross-section A, with a fixed number of turns N increases as

(a) l and A increase.

(b) l decreases and A increases.

(c) l increases and A decreases.

(d) both l and A decrease.

A metal plate is getting heated. It can be because

(a) a direct current is passing through the plate.

(b) it is placed in a time-varying magnetic field.

(c) it is placed in a space varying magnetic field, but does not vary with time.

(d) a current (either direct or alternating) is passing through the plate.

An e.m.f is produced in a coil, which is not connected to an external voltage source. This can be due to

The mutual inductance M12 of coil 1 with respect to coil 2

(a) increases when they are brought nearer.

(b) depends on the current passing through the coils.

(c) increases when one of them is rotated about an axis.

(d) is the same as M21 of coil 2 with respect to coil 1.

A circular coil expands radially in a region of the magnetic field and no electromotive force is produced in the coil. This can be because

(a) the magnetic field is constant.

(b) the magnetic field is in the same plane as the circular coil and it may or may not vary.

(c) the magnetic field has a perpendicular (to the plane of the coil) component whose magnitude is decreasing suitably.

(d) there is a constant magnetic field in the perpendicular (to the plane of the coil) direction.