Diffraction is a characteristic displayed by all types of waves. When a wave encounters an obstacle it does not go straight pass it rather it bends round it. Similarly, when waves encounter a gap the waves spread out the other side of the gap. This characteristic of waves to bend around obstacles and spread out past gaps is referred to as diffraction.
A ripple tank can be used to demonstrate diffraction in waves.
The amount of diffraction depends on the size of the barrier or gap and the wavelength. Light displays diffraction only when it passes through a very narrow gap or slit due to its very small wavelength and this shows that light displays wave properties.
TV and Very High Frequency (VHF) Radio Waves
Radio and TV waves are also diffracted. TV and high frequency radio waves are electromagnetic waves of short wavelengths (about a few meters). When a large barrier such as a tall building or hill obstructs the line of sight from the transmitter the waves cannot bend enough resulting in poor reception for receivers on the other side of the obstruction. In such instances a repeater station is often erected on top of the obstacle so receivers on the other side of the obstacle receive a strong signal.