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AS · Practice questions · The electromagnetic spectrum

One speed, many waves.

Six original Cambridge-style questions on c = fλ, ordering the regions, and the visible range.

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

Shared speed in a vacuum.

01
Analysis
[2 marks]

State two properties that are common to all electromagnetic waves.

  • They are all transverse waves ✓
  • They all travel at the same speed, c = 3.0 × 10⁸ m s⁻¹, in a vacuum ✓
02
Analysis
[2 marks]

A microwave has a frequency of 12 GHz. Taking c = 3.0 × 10⁸ m s⁻¹, find its wavelength.

  • λ = c / f = (3.0 × 10⁸) / (12 × 10⁹) ✓
  • λ = 0.025 m ✓
03
Analysis
[2 marks]

Place these regions in order of increasing frequency: radio, infrared, ultraviolet, gamma.

  • Increasing frequency means decreasing wavelength ✓
  • Order: radio, infrared, ultraviolet, gamma ✓
04
Analysis
[2 marks]

State the approximate wavelength range of visible light in metres.

  • About 4 × 10⁻⁷ m (violet) to 7 × 10⁻⁷ m (red) ✓
  • i.e. 400 nm to 700 nm ✓
05
Analysis
[3 marks]

A gamma ray has a wavelength of 1.0 × 10⁻¹² m. Taking c = 3.0 × 10⁸ m s⁻¹, find its frequency.

  • f = c / λ = (3.0 × 10⁸) / (1.0 × 10⁻¹²) ✓
  • f = 3.0 × 10²⁰ Hz ✓
06
Analysis
[2 marks]

Explain, in terms of the spectrum, why X-rays are more penetrating than visible light.

  • X-rays have a much higher frequency, and so higher photon energy, than visible light ✓
  • The higher energy lets them pass through materials that visible light cannot ✓

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