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How Does Light Interact With Matter?

Alexandrea Dillon, Artem Cheprasov
  • Author
    Alexandrea Dillon

    Alexandrea has taught secondary science for over six years. She has a bachelors degree in Teaching Secondary Science and a Masters of Education in Instructional Design. She's TESOL certified and a National Geographic Certified Educator. In addition, she was the spotlight educator for National Geographic in late 2019.

  • Instructor
    Artem Cheprasov

    Artem has a doctor of veterinary medicine degree.

Learn about the interaction between light and matter in physics. Discover facts, ways, and relationships between light and matter and how they are defined. Updated: 08/17/2022

Table of Contents


Light in Physics

From a scientific standpoint, light is electromagnetic radiation that can be detected by the human eye. Human eyes can usually detect light at the wavelengths between red light, at seven hundred nanometers, and violet light, at four hundred nanometers. A photon is a packet of electromagnetic waves having specific energy. Photons travel as transverse waves. Light is not a type of matter but rather a stream of photons that are transmitting electromagnetic radiation.

This image showcases the entirety of wavelengths available to the human eye, ranging from red at the low end to violet at the high end.

Rectangular bar showing the spectrum of visible light to the human eye, beginning from the left with violet and ending with red.

All electromagnetic waves, including light, can travel through a vacuum. This has been experimentally proven. The speed of light through a vacuum is a scientific constant, usually notated as C. It is famously seen in Albert Einstein's equation, {eq}E = MC^2 {/eq}. In this equation, E = energy, M = mass, and C = the speed of light through a vacuum.

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  • 0:01 Light and Matter
  • 0:34 Binding Energy and…
  • 2:28 Excited Atoms and Photons
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Matter in Physics

Matter is anything that has mass and volume. All matter is made up of atoms, which are comprised of three components:

  1. Protons: Give the atom weight and are positively charged.
  2. Neutrons: Give the atom weight and have no charge.
  3. Electrons: Give the atom negligible weight and are negatively charged.

The protons and neutrons of the atom are clustered together at the center of the atom in a ball of matter known as the nucleus. The electrons orbit around the nucleus.

This carbon atom has six electrons (-) that orbit around six protons (+) and six neutrons.

Artistic representation of a carbon atom with a nucleus and six electrons orbiting it.

An excited atom contains electrons that have moved to a higher level from their original level. Practically speaking, this would look like a much larger orbit around the nucleus than an unexcited atom. The lowest possible level of electron energy is called ground state. Therefore, atoms have multiple permitted energy levels based on their environment. Typically, all diagrams of atoms are in a ground state unless otherwise noted. Binding energy is the amount of energy necessary to remove an electron from its atom. Electrons that are closer to the nucleus tend to be more tightly bound. For example, it would take a greater amount of energy to rip away an electron that is in the first orbital shell at the ground state than an excited electron that is further from its nucleus.

This all leads up to the question, ''Does light have matter?'' The short answer is, no. Light does not have matter, as light is only a form of energy. However, like many things in science, the answer is a little bit more complicated than it seems at first glance. The next sections of this lesson cover that complexity.

Interaction Between Light and Matter

While light is not matter and has no mass, matter can absorb and emit multiple wavelengths of light. How does light interact with matter? There are several different ways a light-matter interaction can occur. Some of these are listed here:

  • Emission: Matter can emit light, such as the filament inside of household light bulbs.
  • Absorption: Matter can absorb light, such as a black roof on a sunny day. This light energy is then converted into heat energy.
  • Transmission: Objects that are transparent transmit light. Windows, crystals, and water are all examples of matter that easily transmit light. Sometimes during transmission, light is refracted. When light is refracted, it changes its speed and direction slightly, which is why objects tend to look bent or distorted when placed under water.
  • Reflection: Mirrors reflect light in specific and predictable ways, which is known as reflection.
  • Scattering: This is sometimes included in the reflection category due to its similarity. However, scattering occurs when light interacts with matter in unpredictable ways with photons bouncing off in all directions. This is common in foggy conditions when photons are randomly bouncing off of the water droplets in the air.

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Frequently Asked Questions

How does light interact with matter and atoms?

Photons, which are discrete packets of light, have wave-particle duality. This means that they sometimes behave like a transverse wave and sometimes behave like a particle. The environment and type of matter being interacted with will define how light and matter interact in any given situation.

What are the different interactions of light?

There are five main different interactions between light and matter in the real world. They are transmission, absorption, scattering, reflection, and emission.

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