(a)(i) Refraction of a wave is the change in the direction of the wave as it moves from one medium to another of different density.
(ii) Critical angle is the angle of incidence in the denser medium beyond which total internal reflection occurs.

(b) (i) The conditions necessary for total internal reflection of wave to occur are:-
- The wave must be travelling from a denser medium to a less dense medium
- The angle of incidence of the wave in the denser medium must be greater than the critical angle of the medium.
(ii) The conditions necessary for interference pattern to be formed are:-
- Two or more sources must be involved.
- The distance between the sources must be of the order of the wave length of the waves

(c) V = \(f \lambda\)
F = \(\frac{v}{\lambda} = \frac{3.6}{0.45}\)
= 8.0Hz

(d) (i)

(ii) n = \(\frac{sin i}{sin r}\)
r = sin\(^{-1} (\frac{sin i}{n})\)
= sin\(^{-1} (\frac{sin 30}{1.5})\)
= 19.5\(^o\)
Deviation = i - r = 30 - 19.5
= 10.5\(^o\)