An electron moving with a velocity $\vec{v}=\left(1.0 \times 10^7\right.$ $\mathrm{m} / \mathrm{s}) \hat{i}+\left(0.5 \times 10^7 \mathrm{~m} / \mathrm{s}\right) \hat{j}$ enters a region of uniform magnetic field $\vec{B}=(0.5 \mathrm{mT}) \hat{j}$. Find the radius of the circular path described by it. While rotating; does the electron trace a linear path too? If so, calculate the linear distance covered by it during the period of one revolution.

(a) Name the parts of the electromagnetic spectrum which are (i) also known as heat waves' and (ii) absorbed by ozone layer in the atmosphere.

(b) Write briefly one method each, of the production and detection of these radiations.

(a) Explain the characteristics of a $p-n$ junction diode that makes it suitable for its use as a rectifier.

(b) With the help of a circuit diagram, explain the working of a full wave rectifier.

Explain the following, giving reasons:

(a) A doped semiconductor is electrically neutral.

(b) In a $p$ - $n$ junction under equilibrium, there is no net current.

(c) In a diode, the reverse current is practically not dependent on the applied voltage.