Plane Mirror. Reflect it.

1. Place a plane mirror upright on a sheet of paper and trace its reflecting edge.
2. Draw the normal at a chosen point on the mirror line.
3. Construct an incident ray at an angle of incidence i from the normal.
4. Place two optical pins (P₁, P₂) on the incident ray, at least 5 cm apart.
5. Look into the mirror to find the images of P₁ and P₂. Move your head until the two images appear in line.
6. Place pins P₃, P₄ so they line up with the images of P₁, P₂.
7. Remove the mirror; join the points to mark the reflected ray.
8. Measure the angle of reflection r from the normal.
9. Repeat for i = 20°, 30°, 40°, 50°, 60°.

Analytical control: plot r against i. The line should be straight through the origin with gradient 1.

• Front- vs back-silvered mirrors — back-silvered mirrors produce a double image; use a front-silvered mirror if possible.
• Pin alignment — sight pin images carefully so all four pins line up visually.
• Pencil thickness — use a sharp pencil so the rays drawn are thin and precise.
• Mirror movement — once traced, do not move the mirror.
• Protractor reading — measure angles from the normal, not from the mirror surface.

• Plane mirror in a holder
• Soft board / pin board
• A4 plain paper
• Four optical pins (P₁, P₂, P₃, P₄)
• Sharp pencil and ruler
• Protractor (resolution ± 1°)

• 3.2.1 Reflection of light — define the terms normal, angle of incidence and angle of reflection; recall and use the law of reflection (i = r); describe an experiment to verify the law of reflection.
• Characteristics of an image formed by a plane mirror — same size as object, same distance behind the mirror as the object is in front, virtual, upright, laterally inverted.