When I say, sound waves can bend, it cannot be observed in open space. Suppose, a man speaks from the stage in a hall and you are standing outside the hall. You can still hear his speech. It proves that the sound waves bend around the doors and windows and reach you. Wavelength of sound and width of door are comparable. Hence the bending of waves or diffraction can easily be observed.
The light waves are very very small. So its bending cannot be observed through house doors. So we have to construct small slits suitable to it's wavelength.
A piece of glass is taken and using a diamond needle, so many lines (rulings) are drawn on it. Nearly 5000 lines per mm. The rulings are opaque and the space between the rulings are transparent. Hence they act as 5000 slits per mm. Now the slits are comparable to the size of light's wave. This device is called 'grating'.
If the light is passed through grating, it will bend at all the thousands of slits. All the bent light rays in a particular direction can be brought to focus using a lens. Now the diffraction of light can be easily observed and studied.
The diffraction grating is widely used in the place of prism.
Note: Arrangements of atoms in some crystals act like a natural grating.
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