Light of wavelength `5000Å` falls on a plane reflecting surface. What are the wavelength and frequency of reflected light ? For what angle of incidence is the reflected ray normal to the incident ray ?

Explanation

Here, `lamda = 5000 Å = 5 xx 10^-7 m`
`v = ( c)/(lamda) = (3 xx 10^8)/(5 xx 10^-7) = 6 xx 10^14 hertz`
On reflection, there is no change in wavelength or frequency. Therefore,
`lamda' = lamda = 5000 Å , v' = v = 6 xx 10^14 Hz`
for reflected ray to be normal to incident ray,
`i+ r = 90^@` or `i+ i= 90^@` `(because r = i)`
`:. i= 90//2 = 45^@`.