Question #ea4f0

1 Answer
Aug 10, 2017

We know the following relation of refractive index (mu) of the prism with the angle of prism (A) and minimum deviation (del_m)

mu=sin((del_m+A)/2)/sin(A/2)

As per given condition we have del_m=A

So we have

mu=sin((A+A)/2)/sin(A/2)

=>mu=sinA/sin(A/2)

=>mu=(2sin(A/2)cos(A/2))/sin(A/2)

=>cos(A/2)=mu/2

=>A=2cos^-1(mu/2)

If we take for glass mu=1.5

Then A=2cos^-1(1.5/2)=82.8^@

If we think otherwise

This relation reveals that the value of A increases with decrease in value of mu and A will be maximum when mu is minimum.The medium of the material of the prism is optically denser than the surrounding medium. So the minimum value of the refractive (mu ) of the medium with respect to the surrounding one may be taken as ~~1.

Imposing this condition we can have the maximum value of A.

Hence " "A_"max"=2cos^-1(1/2)=2xx60^@=120^@