A thin prism of angle `15^(@)` made of glass of refractive index `mu_(1)=1.5` is combined with another prism of glass of refractive index `mu_(2)=1.75`. The combination of the prism produces dispersion without deviation. The angle of the second prism should be

Options

A. `5^(@)`
B. `7^(@)`
C. `10^(@)`
D. `12^(@)`

Answer

C

Explanation

For dispersion without deviation
`delta_(1)+delta_(2)=0,(mu_(1)-1)A_(1)+(mu_(2)-1)A_(2)=0`
`A_(2)=-((mu_(1)-1)A_(1))/((mu_(2)-1))=-((1.5-1)15^(@))/((1.75-1))=-10^(@)`
`-ve` sign shows that two prisms must be joined in opposition.