Definition of Diffraction of Light

Written by david r. wetzel
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Definition of Diffraction of Light
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Diffraction of light is the bending of light waves around an object. The amount of light diffracted or which changes direction is dependent on an object's size. This also applies to light waves that pass through an opening, such as the aperture of a camera or through the pupil of an eye. As light waves pass around the edge of an object or through an opening, light is diffracted or broken into the colours of the rainbow.

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Facts

The deviation of the direction light is travelling occurs when the light passes around the edge of an object. The amount of bending which occurs is based on the wavelength of the light or the objects size in relation to light's wavelength. In addition to bending, light is sometimes broken into its basic components. These components are the colours of the rainbow red, orange, yellow, green, blue, indigo and violet (ROYGBIV).

Red light has the longest wavelength, while violet has the shortest. This is why red is typically the prominent colour in a rainbow and appears to be wider than violet light. This also accounts for a red sky just before sunset or just after sunrise. Occasionally water vapour in the air causes the red light to separate readily from the other colours as the light waves been around the droplets of water.

Full lunar eclipses permit light waves to bend around the edges of the moon to let the side facing earth remain visible, albeit an orange-brown colour instead of the white colour. This is a due to the distance of the moon from earth, allowing the moon to completely cover the sun. Sunlight then bends around the edges of the moon to provide the orange-brown colour.

Interference of the light waves with each other causes the diffracted light to become brighter or dimmer during the diffraction process. Amplification interference causes the light to become brighter and cancellation interference causes the light to become dimmer.

Definition of Diffraction of Light
Light wave diffracting through an opening and around an object

Function

Bending of light also occurs in diffraction grating which has tiny slits cut in the material. Diffraction grating is made from paper, plastic, metal or other materials that cause the light waves to separate into the colours of the rainbow as the light passes through the tiny slits. The size of the slits cut in diffraction grating material are extremely small and may contain as many as 13,500 per inch.

Parallel tiny grooves in a polished surface, such as plastic, also cause the diffraction of light. One example of polished surfaces with parallel tiny groves is a compact disk (CD). The sharp edges of these groves cause the light to bend and separate into the colours of the rainbow.

Definition of Diffraction of Light
Diffraction grating material effects

Significance

Appearance of a rainbow is the result of the diffraction of light. As sunlight encounters water droplets in the air, the light is broken into the colours of the rainbow. This typically occurs just before or after it rains and the air contains a large amount of water vapour or water droplets.

Separation into the colours of the rainbow also occurs when a CD is placed at an appropriate angle in relation to a light source. The light waves bend around the edges of the groves cut into the CD and separates into the colours of the rainbow.

Definition of Diffraction of Light
Rainbow caused by diffraction

Effects

Twinkling stars are another example of diffraction of light. As light from stars pass through the earth's atmosphere which is laden with water vapour, the light bends around the water droplets causing the twinkling effect. The light waves become brighter or dimmer and the colours constantly change due to amplification or cancellation interference.

Misconceptions

Often diffraction and refraction of light are confused with each other. Refraction of light is caused by light passing through transparent material, such as water, that causes the speed of the light wave to slow down and bend. Light is not separated into the colours of the rainbow, as with diffraction.

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