A ray of light passes from vaccume into a medium of refractive index n. if the angle of incidence is twice the angle of refraction, then the angle of incidence is

Options

A. `2 sin^(-1)""(n/2)`
B. `2 cos^(-1)""(n/2)`
C. `cos^(-1)""(n/2)`
D. `2sin^(-1)(n)`

Answer

B

Explanation

`n=( sin i)/(sin r)=(sin i)/(sin""((i)/2))=(2 sin""((i)/2)cos""((i)/(2)))/(sin""((i)/(2)))`
`=2 cos ""((i)/(2)):. (n)/2= cos ""((i)/2) :. i=2cos^(-1)""((n)/2)`