A ray of light travelling through rarer medium is incident at very small angle i on a glass slab and after refraction its velocity is reduced by 20%. The angle of deviation

Options

A. `(i)/8`
B. `(i)/5`
C. `(i)/2`
D. `(4i)/5`

Answer

B

Explanation

`n=(v_a)/(v_m)=(sin i)/(sin r)=(i)/(r) ` for small angles
`(v_a)/((8)/(10)v_a)=(i)/(r) " " :. (10)/(8) =(i)/(r)`
`:. 5r=4i " " :. r=(4)/(5)i`
angle of deviation `delta=i-r=1-(4)/(5)i=(1)/(5)i`