Lesson Plan

• Describe the physical meaning of each term in the grating equation d sin θ = nλ.
• Apply the grating equation to calculate wavelength, grating spacing, or diffraction angles from given data.
• Analyse experimental data from a diffraction‑grating setup and determine the maximum observable order.
• Predict how changes in wavelength or grating spacing affect the diffraction angles.

• Projector and screen
• Diffraction grating slides (e.g., 500 lines mm⁻¹)
• Laser pointer (monochromatic source)
• Protractor or angle‑measuring app
• Worksheet with practice questions
• Scientific calculators

Imagine being able to separate the colours of light like a prism, but using a thin piece of glass with thousands of lines. Students should already understand interference and the double‑slit path‑difference concept. By the end of the lesson they will correctly use d sin θ = nλ to solve for unknowns and explain the trends.

1. Do‑now (5 min): short quiz on interference and path difference.
2. Mini‑lecture (10 min): derive the grating equation, define each variable, and show a ray diagram.
3. Demonstration (10 min): laser through a diffraction grating; students measure the first‑order angle with a protractor.
4. Guided practice (15 min): work through the provided example (5000 lines cm⁻¹, θ = 20°) together, filling a worksheet.
5. Independent practice (10 min): students solve the three practice questions while the teacher circulates.
6. Check for understanding (5 min): exit‑ticket – one sentence stating how wavelength influences diffraction angle.

We reviewed how the grating equation links spacing, order, wavelength and angle, and confirmed the relationships with real measurements. Students submit their exit‑ticket, summarising the wavelength‑angle link, as a quick retrieval check. For homework, complete the additional set of diffraction‑grating problems in the textbook.