What proves that light is a wave?

Answer 1

This is a simple experiment you can do at home. Take three pieces of white cardboard - business cards are perfect. Cut a very narrow slit in the first piece of cardboard. Cut two very narrow slits - about a half inch apart - in the second piece of cardboard. NOTE: The slits only need to be an inch or two long. It is really important to make very narrow slits - as narrow as your scissors will allow. Make sure the slits are evenly cut, so that they are the same narrow width thoughout the length of each slit. Also, make sure the slits on the second card are parallel. Set up a lamp on a flat desk or table with a bare light bulb so that the light bulb is about two or three feet above the table. Hold the first piece of cardboard (with one slit) very close to a light bulb. Do not let it touch the light bulb to avoid risk of fire. Now hold the second piece about two feet below the first card, so that the light that passed through the slit on the first card falls around both slits of the second cardboard. Now place the third piece of cardboard (with not slits) on a table below the cardboard with two slits. All three pieces of cardboard should be lined up so that the light passes first through the cardboard with one slit, and then through the cardboard with two slits, and then onto the cardboard with no slits. Observe the light striking the third piece of cardboard. You will see many bands of lighter and darker areas. If you do not see it right away, move the cardboard with two slits up and down slowly to adjust the focus on the third card. These bands of alternating bright and dark zones are called interference patterns, and are a function of wave interaction. Waves of light pass through the slits of the second piece of cardboard (the one with two slits), and the waves from the two slits combine to make the light brighter at some points (constructive interference), or cancel to make the light darker at other points (destructive interference), thus creating the interference pattern. You can create the same interference pattern on a perfectly smooth pond, puddle, or bath tub by dropping in two small pebbles about two or three feet apart simultaneously. As you watch the ripples radiate outward from the two impact points, the waves will combine in some points to make even higher waves, and will cancel each other out in other points.

Answer 2

by diffraction. when a light wave hits water or glass, it diffracts into separate waves (colors) due to their different wavelength, the way the sunlight diffracts after raining, giving us rainbows

Answer 3

We can prove that light is a wave by the Interference phenomena. A typical example is the existence of alternating light and dark bands, which had been exhibited by Sir Isaac himself in a phenomenon called Newton's rings. The manner in which two trains of waves combine depends upon how their oscillations relate to each other. It they are in step, then crest coincides constructively with crest, giving maximum mutual reinforcement. When this happens in the case of light, one gets a band of brightness, but many times the crest coincides with the trough in mutually destructive cancellation, and one gets a band of darkness.

But according to new research in the field of Quantum mechanics, light exhibits properties of both a particle and wave. Popularly called as the wave-particle duality of light.

Hope this answer helped you.

Answer 4

The clearest evidence that light is a wave is the formation of interference patterns when light passes through a double slit (and in other situations such as the use of a diffraction grating).

Answer 5

You can pass the light through a prism and split the different wavelengths.

Visible (white) light is made up of different wavelengths. Each wavelength travels at a slightly different speed when passing through glass.

A prism is a small glass pyramid, with the sides cut and polished at angle.

As the light passes from air to glass and then back from glass to air, the different speeds, cause the light to bend as it passes through.

This can be projected onto a screen and the different single colors can be displayed.

Answer 6

I assume you mean, how to measure it. The method used by Ole Roemer is fairly easy to understand; check the Wikipedia article "Rømer's determination of the speed of light". Modern methods are much more accurate, but they are also a bit more confusing to understand.

Answer 7

Polarization and interference are evidence of the wave nature of light.

Answer 8

This is known because of different phenomena that are due to light, for example, refraction patterns in light, and interference experiments such as the double-slit experiment.