A thin prism `P_(1)` of angle `4^(@)` and refractive index `1.54^(@)C` is combined with another thin prism `P_(2)` of refractive index 1.72 to produce dispersion without deviation. The angle of `P_(2)` is

Explanation

In case of thin prism `delta = (mu-1)`A, when two prisms are combined together,
` delta = delta_1 + delta _2 = ( mu -1) A+ ( mu .-1) A `
For producing dispersion without deviation
` delta = 0 i.e., (mu.-1)A.=-(mu-1)A `or
`A.=- ((.54 -1))/((1.72 -1)) xx 4^@ =-3^@ `
So the angle of the other prism is `3^@` and opposite to the first.