Explain with the help of a diagram why a pencil partly immersed in water appears to be bent at the water surface.

Use this table  to give an example of 

(i) a medium pair so that light speeds up when it goes from one of these medium to another.

(ii) a medium pair so that light slows down when it goes from one of these medium of another.

(a) With the help of a ray diagram, show that when light falls obliquely on a side of a rectangular glass slab, the emergent ray is parallel to the incident ray.

(b) Show the lateral displacement on the ray of diagram.

(a) A ray of light is incident at an angle of $45°$ at the interface of medium (1) and medium (2) as shown in the diagram. Redraw this diagram in your answer sheet and complete it. If the angle of refraction is $30°$, find the refractive index of medium (2) w.r.t. medium (1).$\left[Given: \sin 45°=\frac{1}{\sqrt{2}} and \sin 30°=\frac{1}{2}\right]$

(b) If the second medium is water in place of medium (2), will the angle of refraction increase or decrease? Why? (Refractive index of water$=\raisebox{1ex}{$4$}\!\left/ \!\raisebox{-1ex}{$3$}\right.$).

(a) State the laws of refraction of light. Explain the term absolute refractive index of a medium and write an expression to relate it with the speed of light in vacuum.

(b) The absolute refractive indices of two media 'A' and 'B' are $2.0 \mathrm{and} 1.5$ respectively. If the speed of light in medium 'B' is $2\times {10}^8 \mathrm{m}/\mathrm{s}$, calculate the speed of light in.

(i) Vacuum       (ii) Medium 'A'.