JEE Physics Magnetism and Matter MCQs Set A

Question: Suppose an isolated north pole is kept at the centre of a circular loop carrying a electric current i. The magnetic field due to the north pole at a point on the periphery of the wire is B. The radius of the loop is a. The force on the wire is

• a)

  

• b)

  

• c)

  

• d) Zero

Answer:

Question: If L be the length of a bar magnet then separation between the two poles is nearly

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: Two identical thin bar magnets each of length l and pole strength m are placed at right angle to each other with north pole of one touching the south pole of the other. Magnetic moment of the system is

• a)

  

• b)

  

• c) ml
• d) 2 ml

Answer:

Question:  A solenoid of length 10 cm and radius 1 cm contains 200 turns and carries a current of 10 A. The value of pole strength of each pole is

• a)

  

• b)

  

• c)

  

• d) 2 Am

Answer:

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: M/2, m

Question: A steel wire of length l has a magnetic moment M. It is then bent into a semi-circular arc. The new magnetic moment is

• a)

  

• b)

  

• c)

  

• d) M

Answer:

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: 27 : 1

Question:

• a)

  

• b)

  

• c)

  

• d) Zero

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: A magnetic needle lying parallel to a magnetic field requires W units of work to turn it through 60°. The torque needed to maintain the needle in this position will be

• a)

  

• b)

  

• c) 2W
• d) W

Answer:

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: Zero

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: d⁴

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: All of these

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: T/n

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: 2 s

Question:  The magnetic moments of two bar magnets of same size are in the ratio 1 : 2. When they are placed one over the other with their similar poles together, then their period of oscillation in a magnetic field is 3s. If one of the magnets is reversed, then the period of oscillation in the same field will be

• a)

  

• b)

  

• c) 3 s
• d) 6 s

Answer:

Question: Magnetostatic screening or shielding can be created by

• a) Both
• b) Soft iron ring
• c) Super conductor
• d) None of these

Answer: Both

Question: Planets producing larger magnetic field have larger

• a) Rotational speed
• b) Density
• c) Mass
• d) Size

Answer: Rotational speed

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: Iron

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

Question: If a dip circle is placed in a vertical plane at an angle of 30° to the magnetic meridian, the dip needle makes= an angle of 45° with the horizontal. The real dip at that place is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: Vertical

Question:

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: Infinite

Question:

• a)

  

• b)

  

• c)

  

• d) Infinite

Answer:

Question: A magnet is suspended in such a way that it oscillates in the horizontal plane. It makes 20 oscillations per minute at a place where dip angle is 30° and 15 oscillations per minute at a place where dip angle is 60°. Ratio of the total earth’s magnetic field at the two places is

• a)

  

• b)

  

• c) 4 : 9
• d)

  

Answer:

Question: Instruments based on tangent law are most accurate when the deflection is

• a) 45°
• b) 30°
• c) 60°
• d) Any angle

Answer: 45°

Question: The magnetic induction and magnetising field intensity in a sample of magnetic material are B and H respectively. The magnetic susceptibility of the material is

• a)

  

• b)

  

• c)

  

• d)

  

Answer:

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: Diamagnetic

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: Behaves like a paramagnetic substance

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: In a ferromagnetic material net magnetic moment of each domain is zero

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: Magnetic permeability is high and retentivity and coercive force are small

Question: Relative permeability of superconductors is

• a) 0
• b) 1
• c) –1
• d) 0.5

Answer: 0

Question:

• a) 60° below horizontal
• b) 45° above horizontal
• c) 30° below horizontal
• d) 30° above horizontal

Answer: 60° below horizontal

Question:

• a) OQ and OR both should be large
• b) OQ and OR both should be small
• c) OQ should be large, OR should be small
• d) OQ should be small and OR should be large

Answer: OQ and OR both should be large

Question: The work done in turning a magnet of magnetic moment M by an angle of 90° from the magnetic meridian is n times the corresponding work done to turn it through an angle of 60°. The value of n is

• a) 2
• b) 1
• c) 

  

• d)

  

Answer: 2

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: Low hysteresis loss and high permeability

Question: A magnetic needle oscillates in a horizontal plane with a period T at a place where the angle of dip is 60°. When the same needle is made to oscillate in a vertical plane coinciding with the magnetic meridian, its period will be

• a)

  

• b)

  

• c) 2T 
• d) T

Answer: