A plane wavefront incident on a reflecting surface at and angle of `30^(@)` with vertical. Find the angle (acute) of reflected wave with vertical.

Explanation

Consider a plane wavefront OA incident at `30^(@)` with the vertical. ON is normal to the reflecting surface. `angle i` is angle of incidence and `angler` is angle of reflection. According to law of reflection `anglei = angle r=30^(@)`

Reflected ray must be perpendicular to the reflected wavelength (OB) as shown in the figure. Therefore, acute angle made by reflected ray with the vertical is `theta=90^(@)-r`
`=90^(@)=30^(@)=60^(@)`