Photons – Sunshine breaking through the clouds.
When did the first photons appear?
A photon is a tiny little particle of light, far too small to see individually. All light is made of photons (FOE-tahns). The earliest photons probably appeared about fifteen billion years ago, during the Big Bang.
What’s the Big Bang?
What are photons?
More about light
All our physics articles
What’s the speed of light?
Unlike electrons and quarks, photons have no mass, so they can travel at the speed of light (about 186,000 miles per second) – that’s why we call it the speed of light.
What are electrons?
And quarks?
The photon: behind light, radio, TV, sunburns, microwaves and X-rays
Photons behave in some ways like particles, little bits of stuff, and in other ways like waves. It’s not just visible sunlight that is made of photons, but a lot of other kinds of waves like radio waves, television broadcasts, x-rays, and the ultraviolet (UVA and UVB) rays that give you sunburns.
Radiation and sunburns
Radioactivity and nuclear physics
The difference between light and these other kinds of waves depends on the size of the wave – the wavelength. Very short waves are x-rays and ultraviolet rays, that cause sunburn. Visible light like sunlight is made of medium-length waves. Radio and television waves are very long waves. But all of these rays are made of photons.
Showing that photons are particles
Short and long wavelengths
If a photon moves in short wavelengths, like x-rays or ultraviolet rays, then that photon has more energy. It’s like if you were jumping rope quickly, you’d be using more energy than someone who jumped slowly. That’s why you have to be careful how much x-ray radiation or UV rays you get, or you’ll get radiation sickness or a sunburn.
If the wavelength is longer, then that photon will have less energy – that’s why it’s not dangerous to stand in the way of microwaves, or cell phones, or radio or television broadcasts.
Photons and heat
When photons bump into other atoms, some of their energy can get the electrons in those atoms moving faster than they were before – that’s what we call heat.
What is heat?
What is friction?
A friction project
That’s why you get hot sitting in the sun. (Microwaves work differently: they are long waves that hit water molecules just right to make them flip around, and it’s the friction from the water molecules flipping that heats your food.)
Did you find out what you wanted to know about photons? Let us know in the comments!
Learn by Doing – Setting up a Solar Oven
Bibliography and further reading about light:
What is the function of a sunlight photon?
Photons don’t exist for a purpose; they just exist. But from our point of view, sunlight photons carry the energy of the sun to Earth, where they provide the energy for most things that happen on earth, from plants growing to melting ice and snow to solar panels to run your computer and ultimately even things like oil and gas and coal.
Are photons in sunlight?
Photons are sunlight; sunlight is made of billions of photons, like your hand is made of millions of cells.
Standing in front of microwaves isn’t damaging?? Ooooook
Right, it’s not. Microwaves aren’t using short radiation waves, like the kind that come from the sun and give you sunburns. They use long waves, like your television or radio, to push the molecules around. It’s the friction of the molecules hitting each other that heats up your food. It’s no more dangerous to stand in front of a microwave than to stand in front of your radio or television. Which is to say, not at all dangerous.
So if i’m looking at a star in the sky, i’m seeing a stream of photons hitting my retina correct? Do we know the distance between each photon? Why does it seem like a stream of light instead of photon after photon? If just one photon hits my retina do i see a blink of light? Would one photon create a beam of light that goes on infinitely? What would it look like to be behind a photon moving away? Would i be able to see it?
Hi Andy! Yes, looking at a star you see a stream of photons hitting your retina. But photons don’t have mass. A lot of photons can occupy the same space at the same time (that’s how lasers work). So there’s no gap. But also, even if there were a gap (as for example when you watch a movie it’s really just a lot of still pictures), your brain fills in the gaps for you, to give the illusion of continuity.
Your eyes *can* see a single photon, but your brain filters it out unless there are 5 to 9 photons together, to keep your vision from being too confusing to process. (http://math.ucr.edu/home/baez/physics/Quantum/see_a_photon.html).
And no, you couldn’t see a photon from behind – when you see, that’s a photon hitting your eye. A photon moving away from you doesn’t hit your eyes.
Hi.. I have few questions ( Iam not a scientist)
1) what happens when photon hits an electron .
Does it get absorbed in to electron and make it vibrate?
2) what happens when photon hits a proton or neutron?
If a photon hits an electron, some of the photon’s energy will be transferred to the electron. The photon will bounce off in a different direction, at a longer wavelength. The electron will have more energy, and may be broken loose from its atom. If a photon hits a proton or a neutron, nothing much happens, because protons and neutrons are much, much bigger than photons.
Thank you Karen Carr. I learned a lot today.
Wonderful! Thanks for stopping by!
I am not a scientist so please excuse me if my question is nonsense but, if a photon has the properties of particles and waves then if we pass two beams at right angles too each other we should see an interaction of particles colliding and a significant degradation of the light beam on both sides after the point of collision. It appears we see a brighter light through the intersection of the two beams (expected as we now see the combined light of both beams) but the light after the intersection does not appear to be affected.
An ocean wave hitting a cliff will interact with and destroy the cliff, it does not change the nature of the wave, simply its course and the collision absorbs some of the energy, looks much more like the effect of photons (which are not atoms as your notes imply) colliding with atoms. What other characteristics suggest Photons are a form of particle?
I certainly did not intend to imply that photons are anything like atoms! Photons are not atoms. I’m not sure what you think photons could be, other than a kind of particle? You may be interested in this discussion: https://www.physicsforums.com/threads/what-happens-when-two-light-beams-collide.219619/ – basically, there are not very many photons in a light beam compared to the amount of space, so they mostly don’t hit each other when the beams cross. Instead of water, picture a few people walking west, with big spaces between them. They cross another few people walking north, also with big spaces between them. Nobody happens to hit anybody else. If you line the photons up (as in a laser) so that they have a bigger chance of hitting each other, then they do, and you get interference patterns.