Home · A-Level 9702 · Superposition · The diffraction grating · Practice
AS · Practice questions · The diffraction grating

Sharp orders.

Six original Cambridge-style questions on the grating equation, slit spacing and the highest order.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

d sin theta = n lambda.

01
Analysis
[2 marks]

State the diffraction grating equation and define each symbol.

  • d sinθ = nλ ✓
  • d is the slit spacing, θ the angle of the maximum, n the order and λ the wavelength ✓
02
Analysis
[2 marks]

A diffraction grating has 500 lines per millimetre. Find the slit spacing d.

  • d = 1 / N = (1 × 10⁻³ m) / 500 ✓
  • d = 2.0 × 10⁻⁶ m ✓
03
Analysis
[3 marks]

Light of wavelength 5.9 × 10⁻⁷ m falls on a grating with d = 2.0 × 10⁻⁶ m. Find the angle of the first-order maximum.

  • sinθ = nλ/d = (1 × 5.9 × 10⁻⁷) / (2.0 × 10⁻⁶) = 0.295 ✓
  • θ = 17° ✓
04
Analysis
[3 marks]

For the grating and light in question 3, find the highest order of maximum that can be observed.

  • The maximum order has n ≤ d/λ = (2.0 × 10⁻⁶)/(5.9 × 10⁻⁷) = 3.4 ✓
  • So the highest whole order is 3 ✓
05
Analysis
[2 marks]

Explain why a diffraction grating gives a more precise wavelength measurement than a double slit.

  • A grating has many slits, so the maxima are very sharp and bright ✓
  • The angle of a sharp maximum can be measured accurately, giving a precise wavelength ✓
06
Analysis
[3 marks]

Light of wavelength 6.0 × 10⁻⁷ m falls on a grating with d = 2.5 × 10⁻⁶ m. Find the angle of the second-order maximum.

  • sinθ = nλ/d = (2 × 6.0 × 10⁻⁷) / (2.5 × 10⁻⁶) = 0.48 ✓
  • θ = 29° ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.