A radio station broadcasts signals using electromagnetic waves. The waves travel through the air at a speed of 3 × 10⁸ m/s. One station broadcasts at a frequency of 100 MHz and another broadcasts at a frequency of 200 MHz. Describe the wave properties of frequency and wavelength, and explain how the wavelengths of the two stations' signals compare to each other.

Eduqas A-Level Physics — 3.1 Wave properties · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Radio stations broadcast signals as electromagnetic waves. These waves all travel through air at the same speed of 3 × 10⁸ m/s, but different stations broadcast at different frequencies.

Model answer (5 marks)

Frequency is the number of complete waves passing a point each second. Wavelength is the distance between two successive identical points on a wave, i.e. the length of one complete wave. The speed of an electromagnetic wave is given by v = fλ, so at constant speed wavelength and frequency are inversely related. The 200 MHz station has a higher frequency than the 100 MHz station. Therefore the 200 MHz station has a shorter wavelength, while the 100 MHz station has a longer wavelength.

Examiner tips

  • Use the definition of frequency and wavelength verbatim. Include the formula v = fλ and state the inverse relationship. Mention the relative frequencies before comparing wavelengths. Keep the answer to 5 points.

Common mistakes

  • Confusing frequency with wavelength or vice versa. Using the wrong direction of the inverse relationship (claiming higher frequency gives longer wavelength). Forgetting to state that both waves travel at the same speed.

Mark scheme (5 marks)

  1. Frequency is the number of complete waves (cycles/oscillations) passing a point per second
  2. Wavelength is the distance between two successive (identical/corresponding) points on adjacent waves / the length of one complete wave
  3. The wave speed equals frequency multiplied by wavelength (v = fλ), so wavelength and frequency are inversely related at constant speed
  4. The 200 MHz station has a higher frequency than the 100 MHz station
  5. The 200 MHz station has a shorter wavelength / the 100 MHz station has a longer wavelength (because both travel at the same speed but at different frequencies)

Key terms in this question

frequency · wavelength · electromagnetic waves

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