# Do x-rays and gamma rays also contain photons like visible light does?

Do x-rays and gamma rays also contain photons like visible light does? If so, then what makes photons of visible light and other waves different?

The rest mass of a photon is zero, but as it moves at the speed of light, its mass is infinite. By $E=mc^2$, its energy is infinite, but using formula $E=h\nu$, we get finite energy. How is this happening?

• it will form an undeterminant form of 0/0 as for photon v=c and m0( m not) is also zero – syed_ali_mousvi Jul 13 '14 at 14:42

The difference is the Energy (or equivalently, the wavelength). See the picture of the Electromagnetic spectrum . The different nomination comes from the time of the discovery. Your eyes can see the visible part. the radio waves can be observed with antennas, etc. The only difference is the way we observe it. But they are all the same (photons).

Here is a scale of the different wavelength for electromagnetic waves:

The Energy reads $E=mc^2$ for massive particles, which a photon is not. The good relation is: $$E=pc = \hbar c k = h \nu$$ You have to use the complete Einstein relation: $$E = \sqrt{p^2c^2 + m^2c^4}$$

And the energy is always finite.

• Might be good to add that what makes visible light different is not that it has photons, but that our eyes absorb only photons with those ranges. Visible light isn't visible because of anything objective about the photon, it's visible because of our eyes. – Mooing Duck Jul 13 '14 at 17:48
• Expanding on that, it's important to understand that the division of the whole electromagnetic spectrum is entirely subjective: there is not a "hard" limit between, say, gamma rays and X-rays. It's merely a rough way to categorize radiation of different wavelengths according to its properties and uses. – andrepd Jul 13 '14 at 19:55
• actually, the denomation come from the way we can observe it. And before Maxwell work, we didn't know that all the EM spectra was just EM waves – sailx Jul 13 '14 at 20:44

Light (all the electromagnetic radiations) is something like raindrops-each little lump of light is called photon-and if the light is all one color, all the "rain-drops" are the same size.$_1$ The size makes photons of visible light and other waves different.

Credits: $_1$ Richard Feynman-QED, The strange Theory of light and Matter.