A ray of light enters a spherical drop of water of refractive index `mu` as shown in figure.

Q. Considert eh figure of question 60, the angle `phi` for which minimum deviation is produced will be given by

Options

A. `cos^(2)phi=(mu^(2)+1)/(3)`
B. `cos^(2)phi=(mu^(2)-1)/(3)`
C. `sin^(2)phi=(mu^(2)+1)/(3)`
D. `sin^(2)phi=(mu^(2)-1)/(3)`

Answer

b.

Explanation

`(ddelta)/(dphi)=-(4dalpha)/(dphi)+2`
`(ddelta)/(dphi)=0rArr (dalpha)/(dphi)=(1)/(2)`
`a=sin^(-1)((1)/(mu)sinphi)`
`cos^(2)phi=(mu^(2)-1)/(3)`