PYQ NEET- Magnetism And Matter L-4

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 lattice structure of the material of the rod

B) the magnetic field of Earth

C) the present source

D) the induced electric field due to the changing magnetic field

the current source is the correct answer#

Sol:#

As the source of current is switched on, a magnetic field sets up in between the poles of the electromagnet. As we know that a diamagnetic substance when placed in a magnetic field acquires a feeble magnetism opposite to the direction of magnetic field. Also, in the presence of the field (non-uniform), these substances are attracted towards the weaker field, i.e. they move from stronger to weaker magnetic field. Due to these reasons, the rod is repelled by the field produced by the current source. Hence, it is pushed up, out of horizontal field and gains gravitational potential energy.