(a) What is meant by ionisation energy? Write its value for hydrogen atom.

OR

(b) Define the term, mass defect. How is it related to stability of the nucleus?

Draw energy band diagram for an $$n$$-type and $$p$$-type semiconductor at $$\mathrm{T}>0 \mathrm{~K}$$.

Answer the following giving reasons:

(i) A $$p$$-$$n$$ junction diode is damaged by a strong current.

(ii) Impurities are added in intrinsic semiconductors.

(a) Two charged conducting spheres of radii $$a$$ and $$b$$ are connected to each other by a wire. Find the ratio of the electric fields at their surfaces.

OR

(b) A parallel plate capacitor (A) of capacitance C is charged by a battery to voltage $$V$$. The battery is disconnected and an uncharged capacitor (B) of capacitance $$2 \mathrm{C}$$ is connected across $$\mathrm{A}$$. Find the ratio of

(i) final charges on A and B.

(ii) total electrostatic energy stored in A and B finally and that stored in A initially.