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Physics for Kids

Photons and Light

We learned on the light page that light has the unique characteristic of behaving like both a wave and a particle at the same time. We then learned some of the ways that light behaves like a wave. Now we want to explore how light also behaves like a particle. Scientists have named the particles that make up light photons.

What is a photon?

In physics, a photon is a bundle of electromagnetic energy. It is the basic unit that makes up all light. The photon is sometimes referred to as a "quantum" of electromagnetic energy.

Photons are not thought to be made up of smaller particles. They are a basic unit of nature called an elementary particle.

Properties of a Photon

Photons have some basic properties that help define what they are and how they behave. These properties include:
Photons Interact with Matter

Photons behave like particles in that they can interact with matter. In some cases the energy of the photon is absorbed by the matter. In this case the extra energy may be emitted as heat. One example of this is the blacktop of the road getting hot in the sun.

Our eyes also interact with photons. When a photon strikes the eye it is turned into electrical energy that is then transmitted to brain to form an image.

When the energy from photons is absorbed by matter, the matter can emit electrons. This process is called the photoelectric effect. The photoelectric effect is a property of light that is not explained by the theory that light is a wave. This is one of the main reasons that scientists chose to treat light as both a wave and a stream of particles.

Planck's Constant

The relationship between the energy of a photon and its frequency can be described by the following equation:

E = hv

where E is energy, v is frequency, and h is Planck's constant. Planck's constant is always the same (i.e. the "constant") and equals 6.62606957 * 10-34 m2 kg / s.

Fun Facts about Photons

Waves and Sound
Intro to Waves
Properties of Waves
Wave Behavior
Basics of Sound
Pitch and Acoustics
The Sound Wave
How Musical Notes Work
The Ear and Hearing
Glossary of Wave Terms
Light and Optics
Intro to Light
Light Spectrum
Light as a Wave
Electromagnetic Waves
The Eye and Seeing

Science >> Physics for Kids

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