Glossary
Absorption
The process where light energy is converted into another form of energy, typically heat, when it interacts with a medium.
Example:
Wearing a dark shirt on a sunny day makes you feel warmer because the fabric is absorbing more sunlight and converting it to heat.
Angle of Incidence (θi)
The angle between the incident ray and the normal line.
Example:
If a laser beam hits a mirror at 30 degrees from the normal, its angle of incidence is 30 degrees.
Angle of Reflection (θr)
The angle between the reflected ray and the normal line.
Example:
According to the Law of Reflection, if the angle of incidence is 45 degrees, the angle of reflection will also be 45 degrees.
Angle of Refraction (θ₂)
The angle between the refracted ray and the normal line in the new medium.
Example:
When light enters water from air, the angle of refraction will be smaller than the angle of incidence because light slows down.
Critical Angle (θc)
The specific angle of incidence at which the angle of refraction is 90 degrees, beyond which total internal reflection occurs when light travels from a higher to a lower index of refraction.
Example:
For light traveling from water to air, if the angle of incidence exceeds the critical angle, the light will not exit the water but reflect back inside.
Diffuse Reflection
Reflection that occurs on rough surfaces, where incoming light rays are scattered in many different directions, preventing the formation of a clear image.
Example:
You can see a painted wall from any angle because its rough texture causes diffuse reflection, scattering light evenly.
Incident Ray
The incoming light ray that strikes a surface.
Example:
In a laser show, the beam of light traveling from the projector to the mirror is the incident ray.
Index of Refraction (n)
A dimensionless measure of how much light slows down in a medium, calculated as the ratio of the speed of light in a vacuum (c) to its speed in the medium (v), n = c/v.
Example:
Glass has a higher index of refraction than air, which is why light bends significantly when it passes from air into glass.
Law of Reflection
A fundamental principle stating that the angle of incidence (θi) is always equal to the angle of reflection (θr) when light reflects off a smooth surface.
Example:
A pool player uses the Law of Reflection to predict how a billiard ball will bounce off the cushion.
Normal Line
An imaginary line drawn perpendicular to the surface at the point where a light ray strikes it, used as a reference for measuring angles.
Example:
When analyzing light hitting a prism, drawing a normal line helps measure the angles of incidence and refraction accurately.
Reflected Ray
The outgoing light ray that bounces off a surface after reflection.
Example:
When a flashlight beam hits a mirror, the light that bounces back into your eyes is the reflected ray.
Reflection
The phenomenon where light bounces off the surface of a medium.
Example:
When you look into a still pond, you see your own image due to the reflection of light off the water's surface.
Refracted Ray
The light ray that passes through into a new medium after bending due to refraction.
Example:
When light enters a diamond, the path it takes inside the gem is the refracted ray.
Refraction
The bending of light as it passes from one medium to another due to a change in its speed.
Example:
A straw in a glass of water appears bent at the water's surface because of the refraction of light.
Snell's Law
A formula (n₁sinθ₁ = n₂sinθ₂) that describes the relationship between the angles of incidence and refraction and the indices of refraction of the two media.
Example:
Engineers use Snell's Law to design lenses that focus light precisely, such as in cameras or telescopes.
Specular Reflection
Reflection that occurs on smooth surfaces, where incoming parallel light rays are reflected in an orderly, parallel manner, preserving the image.
Example:
A highly polished chrome bumper on a car creates a sharp, clear image of its surroundings due to specular reflection.
Total Internal Reflection (TIR)
The complete reflection of a light ray within a denser medium when it strikes the boundary of a less dense medium at an angle greater than the critical angle.
Example:
Fiber optic cables transmit data over long distances by using total internal reflection to keep light signals confined within the fiber.
Transmission
The process where light passes through a medium without being absorbed or reflected.
Example:
Sunlight easily passes through a clear glass window, demonstrating the transmission of light through the material.