CBSE Class 12 Physics Electromagnetic Induction Alternating Currents Assignment Set B

Question. Whenever the flux linked with a circuit changes, there is an induced emf in the circuit. This emf in the circuit lasts
(a) for a very short duration
(b) for a long duration
(c) forever
(d) as long as the magnetic flux in the circuit changes.

Answer: D

Question. The area of a square shaped coil is 10^–2 m². Its plane is perpendicular to a magnetic field of strength 10–3 T. The magnetic flux linked with the coil is
(a) 10 Wb
(b) 10–5 Wb
(c) 105 Wb
(d) 100 Wb

Answer: B

Question. A square of side L meters lies in the X-Y plane in a region, where the magnetic field is given by B=Bo (2it+3tj+4kt)T, where Bo is constant. The magnitude of flux passing through the square is
(a) 2 B_o L² Wb
(b) 3 B_o L² Wb
(c) 4 B_o L² Wb
(d) √29 B_o L² Wb

Answer: C

Question. 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 (it+kt)T is present in the region. The flux passing through the loop ABCDEFA (in that order) is
(a) B_o L² Wb
(b) 2 B_o L² Wb
(c) √2 B_o L² Wb
(d) 4 B_o L² Wb

Answer: B

Question. An emf is produced in a coil, which is not connected to an external voltage source. This can be due to
(a) the coil being in a time varying magnetic field.
(b) the coil moving in a time varying magnetic field.
(c) the coil moving in a constant magnetic field.
(d) All of the options

Answer: D

Question. A magnet is dropped with its north pole towards a closed circular coil placed on a table then
(a) looking from above, the induced current in the coil will be anti-clockwise.
(b) the magnet will fall with uniform acceleration.
(c) as the magnet falls, its acceleration will be reduced.
(d) no current will be induced in the coil.

Answer: A

Question. A copper ring is held horizontally and a magnet is dropped through the ring with its length along the axis of the ring. The acceleration of the falling magnet is
(a) equal to that due to gravity
(b) less than that due to gravity
(c) more than that due to gravity
(d) depends on the diameter of the ring and the length of the magnet

Answer: B

Question. Lenz’s law is essential for
(a) conservation of energy
(b) conservation of mass
(c) conservation of momentum
(d) conservation of charge

Answer: A

Question. The self inductance L of a solenoid of length l and area of crosssection 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.

Answer: B

Question. A thin circular ring of area A is held perpendicular to a uniform magnetic field of induction B. A small cut is made in the ring and a galvanometer is connected across its ends in such a way that the total resistance of the circuit is R. When the ring is suddenly squeezed to zero area, the charge flowing through the galvanometer is
(a) BR/A
(b) AB/R
(c) ABR
(d) B² A/A²

Answer: B

Question. Inductance plays the role of
(a) inertia
(b) friction
(c) source of emf
(d) force

Answer: A

Question. A circular coil expands radially in a region of 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.

Answer: B, C

Question. When the current in a coil changes from 8A to 2A in 3 × 10^–2 second, the emf induced in the coil is 2 volt. The self-inductance of the coil, in millihenry, is
(a) 1
(b) 5
(c) 20
(d) 10

Answer: D

Question. A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from
(a) the current source
(b) the magnetic field
(c) the lattice structure of the material of the rod
(d) the induced electric field due to the changing magnetic field

Answer: A

Question. The mutual inductance of two coils depends upon
(a) medium between coils
(b) separation between coils
(c) both on (a) and (b)
(d) none of (a) and (b)

Answer: C

Fill in the Blanks

Question. The phenomenon in which electric current is generated by varying magnetic fields is appropriately called __________.
Answer: electromagnetic induction

Question. The magnitude of the induced emf in a circuit is equal to the time rate of change of __________ through the circuit. 
Answer: magnetic flux

Question. The induced emf Blv is called __________.
Answer: motional emf

Question. Lenz's law is consistent with the law of __________.
Answer: conservation of energy

Question. The self-induced emf is also called the __________ as it opposes any change in the current in a circuit.
Answer: back emf

Question. Physically, the self-inductance plays the role of __________.
Answer: inertia

Question. The retarding force due to the eddy current inhibits the motion of a magnet. This phenomenon is known as __________.
Answer: electromagnetic damping