A beam of parallel rays of diameter `'b'` propagates in glass at an angle `theta` to its plane. Find the diameter of the beam when it goes to air through this face. `(n_(glass)=n)`

Answer

`CD=(dsqrt(1-n^(2)cos^(2)theta))/(sintheta)`

Explanation

`CD=` beam diameter outside
`CD=AC cos r =(AB)/(sin theta) cos r`,
by Snell's law `nxxsin(90-theta)=1xxsin r`
`rArr sin r =n cos theta`
`therefore cos r=sqrt(1-n^(2)cos^(2)theta)`
thereforeCD(b.sqrt(1-n^(2)cos^(2)theta))/(sin theta)`