Einstein's special relativity says that E 2=p 2c 2+m 2c 4. Photons can have energy (E) and momentum (p). The two particles are the photon (already spoken about), and a similar particle, called a gluon, which is a lot like a photon in many ways but carries the strong force instead of the electromagnetic one. We do know of two kinds of particles which have zero invariant mass (called "rest mass" by some, but if it's zero, you can never get these particles to be at rest - they always travel at the speed of light, c).
Well, we sure didn't define matter in that way. The higher the frequency the more energy per photon. The size of those lumps (or "quanta") of energy depends on the frequency. What that means is that when light is absorbed or emitted, the energy in the wave comes in lumps.
Sometimes you'll hear that light is made of photons. Then waves with higher frequency are called X-rays and still higher are gamma rays - these have the peaks closest together. the different colors of light that people can see), followed by ultraviolet light. Next comes microwaves, then infrared light. For example, radio waves have a pretty low frequency - that is, the peaks in a radio wave are pretty far apart. Electromagnetic waves typically start when an electric charge jiggles back and forth.ĭepending on the "frequency" of the electromagnetic wave (or how scrunched together the peaks in the wave are), you get different kinds of waves.
Light is what's called an "electromagnetic wave", just like radio waves, microwaves, X-ray waves, etc.
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