Three prisms of crown glass, each have angle of prism `9^(@)` and two prisms of flint glass are used to make direct vision spectroscope. What will be the angle of flint glass prisms if `mu` for flint is `1.69` and `mu` for crown glass is `1.53` ?

Options

A. `11.9^(@)`
B. `16.0^(@)`
C. `15.3^(@)`
D. `9.11^(@)`

Answer

A

Explanation

For no deviation n (n-1) A = (n- 1) (n. -1) A.
`3 xx A_(Cr) (n_(Cr) - 1) = 2 A_(f) (n_(f) - 1)`
`rArr 3 xx 9 (1.53 - 1) = 2xx A_(f) (1.6 - 1) = A_(f) = 11.9^(@)`.