Diffraction
When waves meet a gap or an edge in a barrier, they continue through the gap or past the edge of the barrier. This may seem obvious but what happens on the far side of the gap or barrier is not so straightforward.
The waves always 'spread' to some extent into the area beyond the gap.
This is diffraction - the spreading out of waves when they go through a gap, or past the edge of a barrier.
The extent of the spreading (diffraction) depends on how the width of the gap compares to the wavelength of the waves. The wavelength is unchanged after diffraction.
A gap width similar to the wavelength of the waves passing through causes a lot of spreading, eg sound waves passing through a doorway.
A gap width much larger than the wavelength causes little spreading eg light waves passing through a doorway.
The extent of the diffraction also depends on the wavelength of the waves.
The greater the wavelength, the greater the diffraction.
Diffraction affects radio and television signals. Long wave radio signals are much less affected by buildings, hills, tunnels etc. than those of short wave or VHF radio, or television.
