The width of a plane incident wavefront is found to be doubled on refractive in a denser medium. If it makes an anlge of `69Å` with the normal, calculate the refractive index of the denser medium.

Explanation

Data: i= `69^(@), (CD)/(AB)=2`
`=(cos r)/(cos i) = (CD)/(AB)=2`
`therefore cos r = 2 cos69^(@)= 2 xx 0.3584`
`=0.7168`
`therefore r=cos^(-1)0.7168 = 44^(@)12'`
The refractive index of the denser medium relative to the rarer medium
`=(sin i)/(sin r) = (sin 69^(@))/(sin 44^(@) 12') = (0.9336)/(0.6972)= 1.34`