A thin prism having refracting angle `10^(@)` is made of glass of refracting index `1.42`. This prism is combined with another thin prism of glass of refractive index `1.7`. This combination produces dispersion without deviation. The refracting angle of second prism should be `:`

Options

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

Answer

B

Explanation

Thinking proces for dispersion withgout deviation net deviation produced byt the combination of prisms must be zero Let prism angle of the first and second prisms are `A_(1) adnA_(2)` respectively. Similarly , their refractive indices are `mu_(1) and mu_(2)` condition for dispersion without deviation is
`delta_(1)-delta_(2)=0 rArr (mu_(1)-1)A_(1)-(mu_(2)-1)A_(2)=0`
`rArr A_(2)=((mu_(1)-1)/(mu_(2)-1)rArrA_(1)((1.42-1)/(1.7-1)) (10^(10^(@)))rArrA_(2)=6^(@)`