Question

A rod AB moves with a uniform velocity v in a uniform magnetic field as shown in figure.

Options

• The rod becomes electrically charged

• The end A becomes positively charged

• The end B becomes positively charged.

• The rod becomes hot because of Joule heating

Answer 1

The end A becomes positively charged

Due to electromagnetic induction, emf e is induced across the ends of the rod. This induced emf is given by

`e=Bvl`

The direction of this induced emf is from A to B, that is, A is at the higher potential and B is at the lower potential. This is because the magnetic field exerts a force equal to `qvB` on each free electron where q is -1.6 × 10^-16C. The force is towards AB by Fleming's left-hand rule; hence, negatively charged electrons move towards the end B and get accumulated near it. So, a negative charge appears at B and a positive charge appears at A.