JEE Physics Magnetism and Matter MCQs Set A

Question. A long magnetic needle of length 2L, magnetic moment M and pole strength m units is broken into two at the mid point. The magnetic moment and pole strength of each piece will be
(a) M/2, m
(b) M, m
(c) M
(d) 2M

Answer: A

Question. Points A and B are situated perpendicular to the axis of a small bar magnet at large distances x and 3x from its centre on opposite sides. The ratio of the magnetic fields at A and B will be approximately equal to
(a) 27 : 1
(b) 9 : 1
(c) 1 : 9
(d) 2 : 9

Answer: A

Question. A magnetic dipole is placed at right angles to the direction of lines of force of magnetic induction B. If it is rotated through an angle of 180o, then the work done is
(a) Zero
(b) –2MB
(c) MB
(d) 2MB

Answer: A

Question. Two small bar magnets are placed in a line at certain distance d apart. If the length of each magnet is negligible compared to d, the force between them will be inversely proportional to
(a) d⁴
(b) d³
(c) d
(d) d²

Answer: A

Question.  Which of the following statements regarding magnetic lines of force is correct?
(a) All of these
(b) They may or may not pass through a conductor
(c) They need not be perpendicular to the surface from where they start or where they meet
(d) Total magnetic flux linked with a closed surface is always zero

Answer: A

Question. A magnetic needle of negligible breadth and thickness compared to its length, oscillates in a horizontal plane with a period T. The period of oscillation of each part obtained on breaking the magnet into n equal parts perpendicular to the length is
(a) T/n
(b) T
(c) T n
(d) 1/T n

Answer: A

Question. The time period of a freely suspended magnet is 4 s. If it is broken in length into two equal parts and one part is suspended in the same way, then its time period will be
(a) 2 s
(b) 4 s
(c) 0.5 s
(d) 0.25 s

Answer: A

Question. Magnetostatic screening or shielding can be created by
(a) Both
(b) Soft iron ring
(c) Super conductor
(d) None of these

Answer: A

Question. Planets producing larger magnetic field have larger
(a) Rotational speed
(b) Density
(c) Mass
(d) Size

Answer: A

Question. To shield an instrument from external magnetic field, it is placed inside a cabin made of
(a) Iron
(b) Plastic
(c) Wood
(d) Diamagnetic substances

Answer: A

Question. A dip needle free to move in a vertical plane perpendicular to the magnetic meridian will remain
(a) Vertical
(b) Horizontal
(c) At an angle of 60° to the vertical
(d) At an angle of 45° to the horizontal

Answer: A

Question. How many neutral points will be obtained when a bar magnet is kept with magnetic moment parallel to earth's magnetic field?
(a) Infinite
(b) Four
(c) Two
(d) One

Answer: A

Question. Instruments based on tangent law are most accurate when the deflection is
(a) 45°
(b) 30°
(c) 60°
(d) Any angle

Answer: A

Question. A frog is levitated in a magnetic field produced by current in a vertical solenoid below the frog is
(a) Diamagnetic
(b) Paramagnetic
(c) Ferromagnetic
(d) Ferrimagnetic

Answer: A

Question. When a ferromagnetic substance is heated to a temperature above its Curie temperature, it
(a) Behaves like a paramagnetic substance
(b) Remains ferromagnetic
(c) Behaves like a diamagnetic substance
(d) Is permanently magnetised

Answer: A

Question. Select the incorrect statement
(a) In a ferromagnetic material net magnetic moment of each domain is zero
(b) In a ferromagnetic material net magnetic moment of each domain is non-zero
(c) In a paramagnetic substance net magnetic moment of each atom/molecule is non-zero
(d) In a diamagnetic substance net magnetic moment of each atom/molecule is zero

Answer: A

Question. Soft iron is used to manufacture electromagnets because their
(a) Magnetic permeability is high and retentivity and coercive force are small
(b) Retentivity is high
(c) Coercive force is high
(d) Area of the hysteresis curve is large

Answer: A

Question. Relative permeability of superconductors is
(a) 0
(b) 1
(c) –1
(d) 0.5

Answer: A

Question. Soft iron is used in many parts of electrical machines for
(a) Low hysteresis loss and high permeability
(b) High hysteresis loss and high permeability
(c) High hysteresis loss and low permeability
(d) Low hysteresis loss and low permeability

Answer: A