(1) 1.5
For a prism of refracting angle A; a ray incident at an angle i1 ; emerges out at angle i2 . The deviation, δ , is
The refractive index μ of prism is given by
Assuming that incident ray has undergone minimum deviation we have
The deviation, for the given incident ray, may not be the minimum value of deviation. We can, therefore, only say that μ is close to 1.5.