Magnetism And Matter

A magnetic dipole is rotated slowly in a uniform magnetic field from an angle of 0 degrees to 90 degrees and then from 90 degrees to 180 degrees. The work done by the external agent during the second rotation compared to the first rotation is

1. Less
2. Equal
3. Greater
4. Zero

A bar magnet is suspended freely inside a region where Earth's magnetic field is negligible. A strong, perfectly uniform magnetic field is then switched on horizontally. Which statement is correct?

1. The magnet translates in the direction of the magnetic field.
2. The magnet experiences only a torque until it aligns with the field.
3. The magnet remains completely unaffected because Earth's field is absent.
4. The magnet experiences a constant force but no torque.

A student argues that if a bar magnet is broken repeatedly into smaller and smaller pieces, one should eventually obtain an isolated north pole. Which statement best explains why this conclusion is incorrect?

1. The north pole disappears because it is weaker than the south pole.
2. Every fragment becomes a complete magnet with both north and south poles.
3. The magnetic moment of each fragment becomes zero after sufficient cutting.
4. The magnetic field inside a magnet is always zero.

Three identical rods made of different materials are brought near the north pole of a strong bar magnet. Rod P is always attracted. Rod Q is always repelled. Rod R is strongly attracted, but after heating above a certain temperature, it is only weakly attracted. The correct identification is

1. P — Paramagnetic, Q — Diamagnetic, R — Ferromagnetic
2. P — Ferromagnetic, Q — Paramagnetic, R — Diamagnetic
3. P — Diamagnetic, Q — Ferromagnetic, R — Paramagnetic
4. P — Paramagnetic, Q — Ferromagnetic, R — Diamagnetic

A magnetic dipole is placed successively in two different magnetic field configurations. Case I: A uniform magnetic field. Case II: A non-uniform magnetic field directed along the same direction everywhere, but whose magnitude increases gradually along the positive x-axis. Which statement is correct?

1. The dipole experiences a net force in both cases but no torque.
2. The dipole experiences torque only in Case II.
3. The dipole experiences no net force in Case I but may experience both force and torque in Case II.
4. The dipole experiences neither force nor torque in either case.

A diamagnetic substance is placed inside a strong uniform magnetic field. Which statement is correct?

1. It experiences a torque tending to align itself with the field.
2. It experiences no net force and no preferred direction of orientation.
3. It is strongly attracted toward the source of the magnetic field.
4. Its magnetic susceptibility becomes positive because the field is strong.

A student states that a current-carrying solenoid is fundamentally different from a bar magnet because one is produced by moving charges while the other is produced by permanent magnetic poles. Which statement best evaluates this claim?

1. The statement is correct because permanent magnets possess isolated magnetic poles.
2. The statement is incorrect because the external magnetic field patterns of a solenoid and a bar magnet are essentially identical.
3. The statement is correct only if the solenoid carries alternating current.
4. The statement is correct because a bar magnet produces a non-uniform field whereas a solenoid always produces a uniform field.

A bar magnet is heated gradually while remaining well below its Curie temperature. Which of the following is most likely to occur?

1. The magnetic moment increases because thermal energy aligns domains.
2. The magnetic moment decreases because thermal agitation partially disturbs domain alignment.
3. The magnetic moment remains exactly constant until the Curie temperature is reached.
4. The magnet suddenly loses all magnetism at an arbitrary temperature below the Curie temperature.

Two magnetic dipoles have magnetic moments M and 2M. They are placed in the same uniform magnetic field such that both experience the same maximum torque. The angle made by the second dipole with the magnetic field must be

1. 90 degrees
2. 60 degrees
3. 30 degrees
4. 45 degrees

A short bar magnet is suspended freely and allowed to settle in Earth's magnetic field. A second identical bar magnet is then placed directly below it with its north pole facing upward, such that the line joining their centers is vertical. The suspended magnet is again allowed to come to equilibrium. Which statement is correct?

1. The magnet continues to point along the magnetic meridian because Earth's field dominates.
2. The magnet rotates so that its axis becomes vertical.
3. The magnet oscillates indefinitely without attaining equilibrium.
4. The magnet remains horizontal but points east-west.

A magnetic dipole having magnetic moment M is placed in a uniform magnetic field B. It is slowly rotated from the stable equilibrium position to the unstable equilibrium position. The work done by the external agent is

1. MB
2. 2MB
3. Zero
4. -2MB

Three identical specimens made of different materials are placed separately in the same non-uniform magnetic field. One moves strongly toward the stronger field region, one moves weakly toward the stronger field region, and one moves slightly away from the stronger field region. The materials are respectively

1. Paramagnetic, diamagnetic, ferromagnetic
2. Ferromagnetic, paramagnetic, diamagnetic
3. Diamagnetic, ferromagnetic, paramagnetic
4. Ferromagnetic, diamagnetic, paramagnetic

A student claims that magnetic field lines can start from the north pole of one magnet and terminate on the south pole of another nearby magnet. Which statement is most accurate?

1. The statement is always correct.
2. The statement is correct only outside magnets.
3. The statement is incorrect because magnetic field lines always form closed loops.
4. The statement is correct only if the magnets have equal magnetic moments.

A magnetic dipole is placed in a uniform magnetic field. It is released from rest while making an angle of 120 degrees with the field. Neglect all friction and damping. Which statement is correct?

1. The dipole will rotate through 120 degrees and finally stop.
2. The dipole will rotate, cross the stable equilibrium position due to inertia, and oscillate about it.
3. The dipole will rotate until it becomes perpendicular to the field and remain there.
4. The dipole will not rotate because the net force on it is zero.

A bar magnet is cut into three equal parts perpendicular to its length. One of the smaller pieces is again cut into two equal parts along its length. Which statement about one of these final pieces is correct?

1. Magnetic moment becomes one-sixth of the original and pole strength becomes one-third.
2. Magnetic moment becomes one-sixth of the original and pole strength becomes one-half.
3. Magnetic moment becomes one-third of the original and pole strength becomes one-half.
4. Magnetic moment becomes one-twelfth of the original and pole strength becomes one-fourth.