Chapter 10.2 Wave Interference and Diffraction Interference

Interference occurs when light from one source mixes with light from another source.Interference Diffraction occurs when light bends around the edge of an obstacle.

The study of light interference and light diffraction is called physical optics. The superposition principle says that the amplitude of a wave is the sum of the amplitudes of both waves when they meet in interference.

If waves are in phase, there is a reinforcement of amplitudes. This is called constructive interference. In waves that are not in phase, there is a partial or complete cancellation of the amplitudes. This is called destructive interference.

If the amplitude of wave 1 is 40 and the amplitude of wave 2 is 60, what is the total amplitude is the waves are in phase? In Phase so add; = 100 If the waves above are out of phase, what is the total amplitude? Out of Phase so subtract; 60 – 40 = 20

Destructive interference is difficult to accomplish since most natural sources of light are incoherent - which means they emit light waves randomly. It is much easier to observe light if the phases of the waves have a fixed pattern. This is called coherent.

A light that has a single wavelength is called Monochromatic. White light from a bulb or from the sun has 7 wavelengths.

If we place a monochromatic light, such as a laser so that the light goes through a single slit, the light is diffracted. The diffraction from the light will cause a pattern of constructive and destructive interference which will be seen as dark and light bands.diffraction

A diffraction grating is an optical device that uses a large number of slits to transmit or reflect light to form a pattern. Gratings are made by scratching very fine lines in a glass with a diamond.

Diffraction Glasses

A diffraction grating allows us to see the colors separated from white light. An optical instrument that uses a diffraction grating to measure wavelengths is called a grating spectrometer.

3D Glasses Put on your glasses!