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Wave Nature of Light. How do you cook an ant on the sidewalk? Get a magnifying glass and focus the sun’s rays on the ant and the ant gets hot! If the ant heats up, the light must have supplied the energy! How did it do this?. Wave Nature of Light.
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Wave Nature of Light How do you cook an ant on the sidewalk? Get a magnifying glass and focus the sun’s rays on the ant and the ant gets hot! If the ant heats up, the light must have supplied the energy! How did it do this?
Wave Nature of Light We saw how Maxwell’s Equations predicted that alternating electric field produced a magnetic field and an alternating magnetic field produced an electric field The theory predicted electromagnetic waves! These waves must transport the energy!
Wave Nature of Light Last fall we saw how water waves could carry energy They make a leaf bob up and down on the surface of a lake when waves roll by So, we know that waves can carry energy We just finished looking at a “ray model” of light to explain reflection and refraction
Wave Nature of Light Why would we think that light is a wave? DIFFRACTION!!! Remember we saw that water waves diffracted around corners when the wavelengths were comparable to the size of the obstacle To see light diffraction, we have to have some small obstacles
Wave Nature of Light Back in the 1600s, Huygens developed an approach that is very helpful “Every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself. The new wave front is the envelope of all the wavelets - the tangent to all of them.
Wave Nature of Light Huygen’s Principle shows how the wave front moves from position AB to position CD. We just create a lot of new little sources and let each one generate a new wave. The combination forms a new wave front!
Wave Nature of Light See how the wavelets at the edges let the light bend around corners!!! As the slit gets smaller, the bending is more obvious.
The Wave Nature of Light The law of refraction is explained by Huygen’s Principle The little wavelets move slower in medium 2 than in medium 1. Doing the tangent shows how the wave fronts bend.
The Wave Nature of Light The second big argument for light being a wave is the phenomenon of interference We looked at wave interference last fall We decided that you just add the amplitudes of the two waves that occupy the same region of space
Young’s Double Slit The sources have to be coherent, that is they have the same phase relationship. The wave peaks must start out in sync at the two slits.
