Q. Refractive index of a rectangular glass slab is μ = √3. A light ray incident at an angle 60° is displaced laterally through 2.5cm. Distance travelled by light in the slab is

(a) 4cm

(b) 5cm

(c) 2.5√3

(d) 3cm

Ans: B

Sol:Angle of incidence = 60°

By applying Snell’s law ,

1×sin60 = √3×sinr

√3/2 = √3×sinr ,

sinr = 1/2

and r= 30°

By applying formula ,

Lateral Shift = t sin(i-r)/cosr

2.5 = tsin(60-30)/cos30

= t (tan30)

2.5 = t(1/√3)

t= 2.5 √3 cm

distance travelled by light in the slab

= t/cosr

= (2.5√3)/cos30 = 5 cm