- Diffraction is the spreading of wave through an aperture or round an obstacle.
- It is observable when the width of the aperture is of the same order of magnitude as the wavelength of the waves.
- The extent of the diffraction effect is dependent on the relative sizes of the aperture to the wavelength of the wave.
• The smaller the size of the aperture, the greater the spreading of the waves (if the width of the aperture is about the same size as the wavelength, λ, the diffraction effect is very considerable).
• Size of the aperture refers to the width of the slit or gap.
Experiments which demonstrate diffraction including the diffraction of water waves in a ripple tank with both a wide gap and a narrow gap
Note : Huygens’ explanation of Diffraction is not mentioned in syllabus.
Generally, the bigger the wavelength in relation to the width of the aperture, the greater is the spreading or diffraction of the waves.
- The diagrams below show the plan view of diffraction of plane water waves through gaps of different width, in a ripple tank. Note that the wavelengths do not change after passing through the gap.
• It is the relative sizes of the aperture to the wavelength that is important.
Application of Diffraction
• The forms of jetties are used for directing currents and they are constructed sometimes of high or low solid projections.
The diagrams below are INCORRECT! Why?
In (c), diffraction effect is right, but wavelength increases, which is incorrect.
In (d), diffraction effect is too much for the given large slit size and the wavelength should not be increasing.
Note : Huygen’s explanation of diffraction is not mentioned in syllabus