What happens to the interference pattern when two coherent sources are

(a) infinitely close, and

(b) far apart from each other

(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.