When a ray is refracted from one medium into another, the wavelegths changes from `6000Å` to `4000Å`. The critical angle for a ray from the second medium will be

Options

A. `cos^-1.(2)/(3)`
B. `sin^(-1).(2)/(3)`
C. `tan^-1.(3)/(2)`
D. `sin^-1.(2)/(sqrt3)`

Answer

B

Explanation

`lambda_1=6000Å`, `lambda_2=4000Å`
The light is passing from medium 2 to medium 1
`mu_2sini=mu_1sinr`
`mu_2sinC=mu_1sin90^@`
`(sinC)/(lambda_2)=(1)/(lambda_1)` (Since `muprop1/lambda`)
`sinC=lambda_2/lambda_1=(4000)/(6000)impliesC=sin^-1(2//3)`