D. C. Pandey Solutions for Chapter: Magnetism, Exercise 9: [ Level 2 ]

Assertion: A magnet suspended freely in a uniform magnetic field experiences no net force, but a torque that tends to align the magnet along the field.

Reason: Net force $mB-mB=0$. But the forces on North and South poles being equal, unlike and parallel make up a couple that tends to align the magnet, along the field.

Assertion: If one arm of a U-tube containing a diamagnetic solution is placed in between the poles of a strong magnet with the level in line with the field, the level of the solution falls.

Reason: Diamagnetic substances are repelled by the magnetic field.

Assertion: Basic difference between an electric line and magnetic line of force is that former is discontinuous and the latter is continuous or endless.

Reason: No electric lines of forces exist inside a charged conductor but magnetic lines do exist inside a magnet.

Assertion: The earth's magnetic field is due to iron present in its core.

Reason: At a high-temperature magnet loses its magnetic property or magnetism.

Assertion: The ferromagnetic substances do not obey Curie's law.

Reason: At Curie point, ferromagnetic substances start behaving as a paramagnetic substance.

Assertion: The properties of paramagnetic and ferromagnetic substances are not affected by heating.
Reason: As temperature rises, the alignment of molecular magnets gradually decreases.

Assertion: A soft iron core is used in a moving coil galvanometer to increase the strength of the magnetic field.

Reason: From soft iron more number of magnetic lines of force passes.

Assertion: Earth's magnetic field inside a closed iron box is less than compared to the outside.
Reason: The magnetic permeability of iron is low.