Lesson Plan

• Describe the conditions required for two waves to interfere.
• Explain temporal and spatial coherence and their impact on interference patterns.
• Calculate resultant intensity using the phase‑difference formula.
• Predict locations of constructive and destructive interference for a given path difference.
• Apply coherence concepts to assess whether a practical set‑up (e.g., double‑slit) will produce visible fringes.

• Projector or interactive whiteboard
• Slide deck with interference & coherence diagrams
• Laser pointer or narrow‑band LED source
• Double‑slit apparatus or simple slit mask
• Ruler/measuring tape for path‑difference checks
• Worksheet with practice problems
• Whiteboard and markers

Begin with a quick video of colourful interference fringes to capture interest. Ask students what they already know about waves overlapping and why some patterns are bright while others are dark. Explain that today they will uncover the hidden rules—interference conditions and coherence—that govern these patterns, and they will be able to predict and design experiments by the end of the lesson.

1. Do‑now (5'): Students answer a short question on wave superposition on the board.
2. Mini‑lecture (10'): Define interference, present conditions, and introduce the intensity formula.
3. Demonstration (15'): Live double‑slit experiment with laser; vary path difference and observe constructive/destructive fringes.
4. Guided practice (10'): Work through example calculations of intensity and fringe positions using the formula.
5. Coherence discussion (10'): Explain temporal vs. spatial coherence, show table, relate to laser vs. LED sources.
6. Think‑pair‑share (5'): Students evaluate a scenario (LED source with given bandwidth) and decide if interference will be visible.
7. Recap & check (5'): Quick quiz via Kahoot or exit ticket.

Summarise how interference requires coherent waves and how coherence time and length set the limits for observable patterns. For the exit ticket, ask students to write one condition for interference and one factor that limits coherence. Assign homework: complete the worksheet on calculating fringe spacing and coherence length for different light sources.