A prism of refractive index `mu_1` = 1.42 and prism angle 10° is arranged with another prism of refractive index `mu_2` = 1.7. If this combination gives the dispersion without deviation, then what should be the prism angle of second prism?

Options

A. `6^@`
B. `8^@`
C. `10^@`
D. `4^@`

Answer

A

Explanation

For dispersion without deviation `delta=0`
`therefore delta=delta_1+delta_2`
`0=(mu-1)A+(mu.-1)A.`
`therefore A.=-((mu-1)A)/(mu.-1)`
`=-((1.42-1)xx10)/((1.7-1))=-(0.42xx10)/(0.7)=-6^@`
Negative sign represents that prism angles of prisms are opposite.
`therefore` Prism angle of second prism = `6^@`