(i) Define critical angle.

(ii) State one important factor which affects the critical angle of a given medium.

An electromagnetic radiation is used for photography in fog.

(i) Identify the radiation.

(ii) Why is this radiation mentioned by you, ideal for this purpose?

Two bodies A and B have masses in the ratio 5:1 and their kinetic energies are in the ratio 125:9. Find the ratio of their velocities.

(i) Name the physical quantity which is measured in calories.

(ii) How is calorie related to the S.I. unit of that quantity?