When the mirror is rotated through an angle(∆) the reflect ray is rotated through an angle (2∆).proove it

Consider a plane-reflect and a settled episode beam of light reflecting from the surface at a point θ Before the mirror has pivoted, the edge of occurrence is θ just like the edge of reflection.If the mirror is turned through an edge φ the ordinary is turned by an edge &phi and along these lines the edge of frequency increments to θ +φ. In this way, the edge of reflection should likewise increment by φ to θ+φ The contrast between the last edge of reflection and the underlying edge of reflection and is 2φ 

For a settled episode beam, the point of the reflection is double the edge through which the mirror has pivoted.