# Photons For Kids

Albert Einstein was the first scientist to study and determine the properties of light. He called his theory of light the ‘quantum theory of light”.

He received the Nobel Prize for Physics for his discovery and his experiments and explanations that proved his theory.

Other scientists have followed Einstein’s reasoning and have also studied light (what it is, what it does or does not do).

They have agreed that light travels in waves and is made up of particles of electromagnetic energy. They call the particles photons.

Sometimes you may hear the word ‘quantum’ which is another word for a photon.

Einstein made a list of the properties of a photon and how it behaves:

A photon has zero mass. In other words, it has zero weight or is weightless.

A photon has no electric charge. It does not have a positive or negative charge.

A photon is stable. It never changes, but it can be destroyed.

A photon has energy and momentum. It travels in waves.

A photon can interact with other particles, such as electrons.

A photon can be created or destroyed by something in nature.

A photon travels at the speed of light when travelling in empty space.

A photon can be absorbed by matter, which transforms the light into heat, like when sunshine shines down on a pavement, the pavement becomes warm.

Light isn’t the only thing that is made up of photons. All electromagnetic energy is made up of photons, such as microwaves, radio waves and X-rays.

Theses waves can’t be seen by the naked eye, but they exist. How much energy a photon has depends on the wavelength of the light. The wavelength is called frequency.

Energy that has a long wavelength has low frequency and if the wavelength is short, then the frequency is higher.

As light is carried by photons, the photons will have different amounts of energy and will have different wavelengths as they travel.

The photons that have the greatest amount of energy are called gamma rays.

Gamma rays usually have more energy than 100 kilo electron volts (kilo stands for 1000) which is written as 100 keV. Gamma rays that have less than 100 keV’s are X-rays.

Photons that have only 1 eV are part of visible light.

### Questions:

1. What was Einstein’s theory of light?
2. What does ‘no mass’ mean?
3. What is a photon?
4. Name 3 things a photon can do or has.
5. What is the only thing that has photons?