Laws of Reflection

• The two laws of reflection for light on smooth surfaces.
• Regular vs diffuse reflection.
• Image formation in a plane mirror — virtual, erect, same size, lateral inversion.
• Uses: periscope, kaleidoscope, rear-view mirrors.

1. First law — angle of incidence (∠i) = angle of reflection (∠r), measured from normal.
2. Second law — incident ray, reflected ray, and normal lie in the same plane.
3. Plane mirror image — distance behind mirror = object distance; laterally inverted.
4. Regular reflection — smooth surface (calm water, mirror).
5. Diffuse reflection — rough surface scatters light (paper, wall) — still obeys laws at each point.
6. Real world — ambulance lettering reversed; dressing mirror; periscope in submarines.

Finding reflected ray when incident ray makes 35° with normal

Given: ∠i = 35°
Step 1 — Law 1: ∠r = 35° on other side of normal.
Step 2 — Draw normal perpendicular to mirror at point of incidence.
Step 3 — Both rays lie in plane of paper (Law 2).
Step 4 — If object 4 cm from mirror, image is 4 cm behind mirror.

• Measuring angles from mirror surface instead of normal.
• Misconception: rough surfaces don't reflect (they scatter by diffuse reflection).
• Thinking mirror image is real (cannot be projected on screen).
• Confusing lateral inversion with upside-down image.

• State both laws of reflection.
• List three properties of image in plane mirror.
• Why is 'AMBULANCE' written backwards on ambulances?

Open the Practice tab for graded questions on Laws of Reflection.