(i) Define critical angle.

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

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

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

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.