Optics refers to the study of light, which is a very interesting subject. Light particles have wave-like behavior, but also displays particle-like behavior.

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Most modern physics describe light with the photon model. This means that instead of classifying light as a wave or a particle, it is classified as a photon, which is an entity that shows both wave- and particle-like traits. Quantum physics are a heavy topic, but we’ll try to break down why the behavior of light has to be described this way.

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Wave Properties:

Reflection: Waves all have the tendency to bounce off of an obstacle in their path. Light behaves in this way; when it approaches a flat, reflective surface, it will bounce off at the same angle it approached the surface with, which is the law of wave reflection.

Refraction: Waves undergo a change in path when they cross the boundary between two mediums. This is because certain mediums are faster or slower, like it’s easier to run through air rather than water. Light does refract, bending its path when going through a boundary.

Diffraction: Waves will change their direction to go through an opening or around an obstacle. This is easily imagined with water waves, going through a narrow opening and then spreading out once past the barrier. Light does this as well, it’s just a little harder to see. Even though an obstacle in the path of light blocks most light, creating a shadow, careful study of the  shadow shows that interference patterns (the “fuzziness”) are created on the edges. So some light does diffract around the edges of obstacles.

Light Ray: Light always travels in a straight line in free space. Even if two light rays are crossed, they will continue on in straight lines, not interfering. A light ray would also theoretically travel forever if it didn’t have any interactions with other materials. It also travels at constant velocity, the speed of light, in a vacuum.

Photoelectric Effect: Under certain conditions, light can dislodge electrons from types of metal. This effect takes a while to explain in full, but basically what was realized from this finding was that the the atoms in metal can absorb a certain amount of energy from the light, a photon, and photons of light have momentum.

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In summary, photons can be described as having wave-particle duality, properties of waves and particles. In quantum physics, a photon is referred to as the elementary particle of light, or a quantum of light.

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