Physical Science Matric Revision: Electromagnetic Radiation

Revision Notes for CAPS Physical Science Grade 12: Waves, Sound, and Light Electromagnetic Radiation


In Grade 12 Physical Science, the study of Waves, Sound, and Light is fundamental because it explains various natural phenomena and technological applications we encounter daily. This unit covers the properties, behaviors, and applications of waves, sound, and light, as well as how electromagnetic radiation interacts with matter.

Key Points

  1. Waves: Waves transfer energy from one point to another without transferring matter.

    • Transverse Waves: Wave particles move perpendicular to the direction of the wave (e.g., light waves).
    • Longitudinal Waves: Wave particles move parallel to the direction of the wave (e.g., sound waves).
    • Wave Properties: Amplitude, wavelength, frequency, period, and speed with the formula (v = f \lambda) where (v) is wave speed, (f) is frequency, and (\lambda) is wavelength【4:17†source】 .
  2. Sound:

    • Properties of Sound: Speed of sound varies in different media, fastest in solids and slowest in gases.
    • Doppler Effect: Change in frequency or wavelength of sound due to the movement of the source or observer. The formula used is:
      f_L = \left( \frac{v \pm v_L}{v \mp v_S} \right) f_S
      where (f_L) is the frequency heard by the listener, (v) is the speed of sound, (v_L) is the speed of the listener, and (v_S) is the speed of the source .
  3. Light:

    • Properties of Light: Light behaves both as a wave and as a particle (wave-particle duality).
    • Electromagnetic Spectrum: Range of all types of electromagnetic radiation.
    • Photoelectric Effect: Emission of electrons when light hits a material. This can be described by the equation:
      E = hf = \frac{hc}{\lambda}
      where (E) is energy, (h) is Planck’s constant, (f) is frequency, (c) is the speed of light, and (\lambda) is wavelength .

Real-World Applications

  1. Doppler Radar: Used in meteorology to detect the speed of rain particles and predict weather patterns.
  2. Medical Imaging: Technologies like ultrasound utilize sound waves to create images of the inside of the body.
  3. Telecommunications: Light waves in fiber optics are used for high-speed internet.
  4. Photoelectric Sensors: Used in various applications like automatic doors and night-time lighting .

Common Misconceptions and Errors

  1. Misconception: Higher intensity always means higher energy.
    Correction: Intensity relates to the number of photons, but energy depends on frequency (higher frequency means higher energy, not intensity) .

  2. Misconception: Sound can travel through space.
    Correction: Sound requires a medium (solid, liquid, or gas) to travel; it cannot travel through a vacuum like space.

  3. Misunderstanding: Light always behaves as a wave.
    Correction: Light behaves as both a wave and a particle (wave-particle duality).

Practice and Review

  1. Basic Questions:

    • Explain the Doppler Effect and provide one practical application.
    • Calculate the speed of a wave with a frequency of 50 Hz and a wavelength of 2 meters.
  2. Advanced Questions:

    • Using the formula (E = hf), calculate the energy of a photon with a frequency of (6 \times 10^{14}) Hz.
    • Describe what happens to the wavelength and frequency of a sound wave if the source of the sound is moving towards a stationary listener.


  1. Doppler Effect: The frequency observed increases if the source is approaching and decreases if moving away. Used in radar speed guns.
  2. Wave Speed Calculation:
    v = f \lambda = 50 \, \mathrm{Hz} \times 2 \, \mathrm{m} = 100 \, \mathrm{m/s}
  3. Photon Energy Calculation:
    E = hf = (6.626 \times 10^{-34} \, \mathrm{Js}) \times (6 \times 10^{14} \, \mathrm{Hz}) = 3.98 \times 10^{-19} \, \mathrm{J}

Connections and Extensions

  • Interdisciplinary Links: Doppler Effect’s connection with weather prediction (Geography), use of waves in communication systems (Information Technology).
  • Real-World Implications: Understanding the fundamental properties of light and sound can lead to innovations in medical technology, telecommunications, and even space exploration.

Summary and Quick Review

  • Waves transfer energy without transferring matter, have properties such as amplitude, wavelength, and frequency.
  • Sound is a longitudinal wave, and its behavior can be described by properties like speed, frequency, and Doppler Effect.
  • Light behaves as both a wave and a particle; its interactions lead to technological advancements like photoelectric sensors and fiber optics.

Additional Resources:

By carefully studying these revision notes, working through the practice problems, and utilizing the additional resources, you can excel in your understanding of Waves, Sound, and Light.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.