1.6 Short Notes: Diffraction of Waves

Diffraction of Waves

  • Diffraction of waves occurs when waves are spread out when passing through a narrow gap.
  • Diffraction is easily can be seen when the size of gap is less than the wavelength of the waves.
  • Figure 1.24 shows how diffraction works when a gap is placed at the middle of the wave propagation. Larger gap produces small diffraction while smaller gap produces large diffraction.

Diffraction of sound wave

  • Figure 1.25 shows a student is walking on a corridor. When reaching the turn, he could listen to the music on the radio that was placed behind the turn.
  • This is due to diffraction of sound waves. Sound waves travel in circular motion and when it passes through the turn, the waves still able to travel to the other corridor.

Diffraction of light

  • Figure 1.26 shows how diffraction of light works. A light source (commonly known as monochromatic light) passes through a very narrow slit and projected on a screen.
  • The bright fringes show that the light waves does not intersect each other while dark fringes shows there are intersections between light waves.


  1. How does water diffracts when passing an obstacle that is the same length as the wavelength of the wave?
  2. What are the factors that affect sound wave when it diffracts?
  3. What if a monochromatic light source passes through a wide slit?


  1. There is no diffraction occur.
  2. Direction of wave.
  3. The gap between bright fringes and dark fringes increases.