2A.4 – Angle of Deviation

Angle of deviation θ of a light ray is the angle between its incident direction and its reflected direction.

We say that a light ray is “deviated from its original path” through this angle θ.

If possible state direction too, such as clockwise or anticlockwise.

 

Example
A light ray reflects on a mirror as shown below.

(a) What is the angle of incidence of this ray?

40º (as the normal will lie half way between these two rays)

 

(b) What is the angle of deviation that this light goes through?

180º – 80º = 100º in an anti-clockwise direction

 

2025 Physics Lessons