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# What is light, particles, waves or both

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What is light? Is it a particle, wave, or both? Define the wave properties: period, wavelength, amplitude and frequency. What is c? How does c relate to wavelength and frequency?

https://brainmass.com/physics/speed-of-light/light-particles-waves-both-343668

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Classical, from classical electrodynamics of Maxwell, light is the propagation of disturbances in the continuum of electric field. Just as water waves are propagation of any disturbance in the "matter field" of the water or "water field".
Now from the viewpoint of quantum theory, light consists of some physical entities called photons which are referred to as particles but are not quite particles as we explain in the following. First of all photons are responsible for exchange of electric force: When two charges exert force on each other, they are actually sending and receiving photons to each other, thereby acting on the other body and exerting force on it.
But is light or photons particles or waves? Based on standard interpretation of quantum theory, we can not say anything about a system before measurement. We can only say what happened at the measurement time. So photos or light is both wave and particle in the sense that it behaves wavelike in some measurements like when we perform the interference experiment and it is a particle in the sense that it behaves as it is a particle in some other experiments like the photoelectric effect. We can not say whether it is a wave or particle before measurement. We can just say that at the moment of measurement, for some experiments it behaves like waves and for some experiments it behaves like particles.
In the classical viewpoint light is wave so it has properties of waves as period, wavelength, amplitude and frequency. So what are they?
Period: Just as every point in the water moves up and down while it is sitting in its own place and not moving back or forth, points in electric field do the same. The amount of time which it takes for a point on a point in water or electromagnetic field to move from its position and then again return back to that same state is called period.
Wavelength: If you look at a water wave, you see sum peaks equally spaced from each other moving in the water. Note that the water itself doesn't move. It is just that disturbance in the form of a sine function which is moving. The particles of water are just moving up and down while sitting on a same position. Now the distance between two consecutive peaks or two consecutive valleys or more generally two consecutive points on the wave with the same state is called a wavelength.
Amplitude: Each point in water wave in moving up and down. The maximum amount of distance that they move up (or down) from flat surface of water (the surface of water when there were no wave) is called amplitude.
Frequency: Frequency is the number of times that a point on a wave starts from a position and goes back to it in a second. For example if a point on the wave in now on its peak and in 1 second it goes dawn and back up three more time (totally 4 times) then its frequency is 4. Because in 1 second it has touched its peaks four times during its periodic motion up and down around the flat surface of water.
C: C is the speed of light or the speed of propagation of disturbance in the electric field. It is the measure of how fast light goes from one place to another. The relation of c to wavelength L and frequency f is as follows:

c=L*f