Lesson Plan

• Describe the law of reflection and its geometric representation.
• Construct accurate ray diagrams for plane mirrors using the normal and incident ray.
• Measure angles of incidence and reflection and calculate Δθ to verify the law.
• Calculate object and image distances for plane mirrors and interpret sign conventions.
• Analyse common errors in measurements and diagram construction.

• Plane mirror (small tabletop)
• Protractor or digital angle measurer
• Ruler or metre stick
• Laser pointer or ray box
• Whiteboard and markers
• Worksheet with measurement table
• Projector for demonstration

Begin with a quick demonstration of a bathroom mirror to highlight how everyday mirrors follow simple geometric rules. Ask students what they already know about angles and how light behaves when it hits a smooth surface. Explain that today they will construct ray diagrams, take precise measurements, and use calculations to confirm the law of reflection. Success will be measured by accurate diagrams, correct angle calculations, and a clear explanation of the virtual image.

1. Do‑now (5') – Quick quiz on previous optics concepts (angle terminology, image types).
2. Mini‑lecture (10') – Present the law of reflection, virtual image properties, and demonstrate a ray diagram on the projector.
3. Guided construction (10') – In pairs, students draw a ray diagram on their worksheet, marking the mirror, normal, incident ray, reflected ray, and virtual image.
4. Practical measurement (10') – Set up the mirror, laser pointer, and protractor; record object distance, incident angle, and reflected angle for three trials.
5. Data analysis (5') – Calculate Δθ for each trial and compute image distance using d_i = –d_o; discuss accuracy.
6. Error analysis & discussion (5') – Identify common mistakes (measuring from the mirror surface, sign errors) and correct them.
7. Exit ticket (5') – One‑sentence summary of how the experiment verified the law of reflection.

Review the key points: the incident and reflected rays make equal angles with the normal, and a plane mirror forms a virtual, upright image at the same distance behind the mirror as the object is in front. Collect exit tickets to gauge understanding, and assign a short homework task to complete a ray‑diagram worksheet with a new set of measurements.