CBSE Class 12 Physics Magnetism and Matter MCQs Set B

Question. A frog can be levitated in a magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as :
(a) paramagnetic
(b) diamagnetic
(c) ferromagnetic
(d) antiferromagnetic

Answer : C

Question. Domain formation is the necessary feature of :
(a) ferromagnetism
(b) diamagnetism
(c) paramagnetism
(d) all of the options

Answer : A

Question. The best material for the core of a transformer is
(a) mild steel
(b) stainless steel
(c) soft iron
(d) hard steel

Answer : C

Question. What happens, when a magnetic substance is heated ?
(a) It loses its magnetism
(b) It becomes a strong magnet
(c) Does not effect the magnetism
(d) Either (b) and (c)

Answer : A

Question. A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60° is W. Now the torque required to keep the magnet in this new position is
(a) W/√3
(b) √3W
(c) √3W /2
(d) 2W /√3

Answer : B

Question. Which one of the following are used to express intensity of magnetic field in vacuum ?
(a) oersted
(b) tesla
(c) gauss
(d) none of these

Answer : A

Question. A bar magnet of magnetic moment M is placed at right angles to a magnetic induction B. If a force F is experienced by each pole of the magnet, the length of the magnet will be
(a) MB/F
(b) BF/M
(c) MF/B
(d) F/MB

Answer : A

Question. A magnetic needle suspended parallel to a magnetic field requires 3 J of work to turn it through 60°.
The torque needed to maintain the needle in this position will be
(a) 2√3J
(b) 3 J
(c) √3 J
(d) 3 /2 J

Answer : B

Question. At a certain place, the angle of dip is 30º and the horizontal component of earth’s magnetic field is 0.50 oerested. The earth’s total magnetic field (in oerested) is
(a) √3
(a) 1
(a) 1√3
(a) 1/2

Answer : C

Question. A steel wire of length l has a magnetic moment M. It is then bent into a semicircular arc. The new magnetic moment is
(a) M/π
(a) 2M/π
(a) 3M/π
(a) 4M/π

Answer : B

Question. At a temperatur of 30°C, the susceptibility of a ferromagnetic material is found to be c . Its susceptibility at 333°C is
(a) c
(b) 0.5 c
(c) 2c
(d) 11.1c

Answer : B

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 north pole of a magnet is brought near a metallic ring. Then the direction of the induced current in the ring will be:
(a) Towards north
(b) Towards south
(c) Anticlockwise
(d) Clockwise

Answer : C

Question. Angle of dip is 90° at:
(a) Equator
(b) Middle point
(c) Poles
(d) None of these

Answer : C

Question. A short bar magnet of magnetic moment 0.4 J T–1 is placed in a uniform magnetic field of 0.16 T. The magnet is in stable equilibrium when the potential energy is
(a) 0.064 J
(b) –0.064 J
(c) zero
(d) –0.082 J

Answer : B

Question. A vibration magnetometer placed in magnetic meridian has a small bar magnet. The magnet executes oscillations with a time period of 2 sec in earth’s horizontal magnetic field of 24 microtesla. When a horizontal field of 18 microtesla is produced opposite to the earth’s field by placing a current carrying wire, the new time period of magnet will be
(a) 1 s
(b) 2 s
(c) 3 s
(d) 4 s

Answer : D

Question. The moment of a magnet (15 cm × 2 cm × 1 cm) is 1.2 A-m². What is its intensity of magnetisation?
(a) 4 × 104 A m^–1
(b) 2 × 104 A m^–1
(c) 104 A m^–1
(d) None of the options

Answer : A

Question. The magnetic moment of a diamagnetic atom is
(a) much greater than one
(b) 1
(c) between zero and one
(d) equal to zero

Answer : D

Question. Two points A and B are situated at a distance x and 2x respectively from the nearer pole of a magnet 2 cm long. The ratio of magnetic field at A and B is
(a) 4 : 1 exactly
(b) 4 : 1 approximately
(c) 8 : 1 approximately
(d) 1 : 1 approximately

Answer : C

Question. Two bar magnets of the same mass, same length and breadth but having magnetic moments M and 2M are joined together pole for pole and suspended by a string. The time period of assembly in a magnetic field of strength H is 3 seconds. If now the polarity of one of the magnets is reversed and combination is again made to oscillate in the same field, the time of oscillation is
(a) √3 sec
(b) 3 √3 sec
(c) 3 sec
(d) 6 sec

Answer : B

Question. A magnet makes 40 oscillation per minute at a place having magnetic intensity of 0.1 × 10^–5 tesla. At another place it takes 2.5 sec to complete one oscillation. The value of earth’s horizontal field at that place is
(a) 0.76 × 10^–6 tesla
(b) 0.18 × 10^–6 tesla
(c) 0.09 × 10^–6 tesla
(d) 0.36 × 10^–6 tesla

Answer : D

Question. Magnetic lines of force due to a bar magnet do not intersect because
(a) a point always has a single net magnetic field
(b) the lines have similar charges and so repel each other
(c) the lines always diverge from a single force
(d) the lines need magnetic lenses to be made to interest

Answer : A

Question. A 250-turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 mA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180° against the torque is
(a) 4.55 mJ
(b) 2.3 mJ
(c) 1.15 mJ
(d) 9.1 mJ

Answer : D

Question. A closely wound solenoid of 2000 turns and area of cross-section 1.5 × 10^–4 m² carries a current of 2.0 A. It is suspended through its centre and perpendicular to its length, allowing it to turn in a horizontal plane in a uniform magnetic field 5 × 10^–2 tesla making an angle of 30° with the axis of the solenoid.
The torque on the solenoid will be
(a) 3 × 10^–3 N m
(b) 1.5 × 10^–3 N m
(c) 1.5 × 10^–2 N m
(d) 3 × 10^–2 N m

Answer : C

Question. A bar magnet having a magnetic moment of 2 × 10⁴ J T^–1 is free to rotate in a horizontal plane. A horizontal magnetic field B = 6 × 10^–4 T exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction 60° from the field is
(a) 12 J
(b) 6 J
(c) 2 J
(d) 0.6 J

Answer : B

Question. At a point A on the earth’s surface the angle of dip,d = +25°. At a point B on the earth’s surface the angle of dip, d = –25°. We can interpret that
(a) A and B are both located in the southern hemisphere.
(b) A and B are both located in the northern hemisphere.
(c) A is located in the southern hemisphere and B is located in the northern hemisphere.
(d) A is located in the northern hemisphere and B is located in the southern hemisphere.

Answer : D