A ray of light is incident on a plane mirror at an angle of 40° with respect to surface normal. When it gets reflected from the mirror, it undergoes a deviation of

The correct answer is Option 2 (100°).

According to the laws of reflection, the angle of incidence (i) is equal to the angle of reflection (r). Given that the ray is incident at 40° to the surface normal, the angle of reflection is also 40°.

The angle of deviation (δ) is defined as the angle between the original path of the incident ray and its reflected path. Mathematically, if a light ray were to travel straight without the mirror, it would cover a total linear angle of 180°. The deviation is calculated using the formula: δ = 180° - (i + r) or δ = 180° - 2i.

• Substituting the values: δ = 180° - (40° + 40°)
• δ = 180° - 80°
• δ = 100°

Option 4 (80°) is incorrect as it represents the total angle between the incident and reflected rays, not the deviation from the original path.