a. Irregular reflection – wood

The surface of the wood is rough, and not polished. When light hits such surfaces, the reflected rays scatter in random directions (see figure below). This is called irregular reflection.

b. Multiple reflection – Periscope

Periscopes are used, if the object to be viewed and the observer are not in line-of-sight. Periscope uses multiple mirrors, which allows the light to reflect multiple times so as to reach the observer.

c. Refraction – glass slab

Refraction is the phenomenon where the light ray bends while passing from one medium to another. When light travels from air to glass slab, there is a change in the medium, and hence refraction occurs.

d. Total internal reflection – optic fibre

An optical fibre is a thin fibre made of glass or plastic which allows light to move from one end to the other. The light is incident on the fibre at a small angle, and the light that passes inside undergoes repeated total internal reflections along the fibre and finally comes out.