Law of Reflection: Deviation Angle

Steps:

• Incident ray strikes mirror at angle of incidence i = 40° to the normal.
• Reflected ray leaves at angle of reflection = 40° to the normal (law of reflection).
• Angle between incident and reflected rays is 180° - 2i.
• Substitute i = 40°: 180° - 80° = 100° deviation.

Why C is correct:

• Deviation angle is 180° - 2i; for i = 40°, it equals 100° per reflection law.

Why the others are wrong:

• A: 40° is the angle of incidence, not the deviation.
• B: 90° assumes perpendicular incidence (i=45°), but i=40° here.
• D: 140° would require i=20° (180°-40°), inconsistent with setup.

Final answer: C