Introduction to Light and Its Properties

Light is a form of electromagnetic radiation that can be seen by the human eye
Light travels in a straight line and at a constant speed of 299,792,458 meters per second in a vacuum.

Incandescence: Objects heated to high temperatures emit light.
- Inexpensive, but inefficient as it loses energy as heat.
- Examples include light bulbs and glowing metals.
Electric Discharge: Electric current through a gas produces light.
- Can produce colored light, but often dim.
- Examples include neon signs.
Fluorescence: UV light converted into visible light.
- Energy efficient and lasts longer than incandescent, but contains hazardous mercury.
- Examples include fluorescent tubes.
Phosphorescence: UV light is absorbed and released slowly as visible light.
- Glow lasts for a period of time, but not very bright and fades with time.
- Examples include glow-in-dark items and novelty toys.
Chemiluminescence: Light is produced by a chemical reaction.
- Portable, durable, and inexpensive, but single-use and light is temporary.
- Examples include glow sticks and emergency safety lights.
Bioluminescence: Chemical reaction within a living organism produces light.
- Attracts mates, lures prey, but limited human applications.
- Examples include fireflies, jellyfish, and deep-sea fish.
Triboluminescence: Friction causes crystal breakage, producing light.
- Examples include wintergreen life savers (candy glow).
Light-Emitting Diodes (LEDs): Electric current passed through a semiconductor produces light.
- Very efficient, long-lasting, and durable, but expensive compared to other bulbs.
- Examples include LED bulbs and indicator lights.

Laser light is a type of light that is highly coherent, meaning that all of the light waves are in phase with each other.
Laser light is also highly directional, meaning that it travels in a straight line with very little divergence.
Lasers are used in a wide variety of applications, including:
- Scanning barcodes
- Playing music on CD players
- Performing surgery
- Cutting and welding materials
- Carrying information through fiber-optic cables
Uses the acronym LASER - Light Amplification by Stimulated Emission of Radiation.

Geometric optics is the study of how light interacts with matter.
Reflection is the bouncing of light off of a surface.
The law of reflection states that the angle of incidence is equal to the angle of reflection.
The angle of incidence is the angle between the incident ray and the normal line.
The angle of reflection is the angle between the reflected ray and the normal line.
The normal line is a line perpendicular to the surface at the point of incidence.

Concave Mirror: A mirror curved inwards, converging light rays.
- Objects further than the focal point (F) produce real, inverted images.
- Objects closer than the focal point produce virtual, upright images.
Convex Mirror: A mirror curved outwards, diverging light rays.
- Always produces virtual, upright, and smaller images.
Plane Mirror: A flat mirror that creates a virtual, upright, and laterally inverted image.

Refraction is the bending of light as it passes from one medium to another.
The amount of bending depends on the index of refraction of the two mediums.
The index of refraction is a measure of how much light slows down as it travels through a medium.
Light travels slower in denser mediums.

The index of refraction (n) of a medium is the ratio of the speed of light in a vacuum (c) to the speed of light in the medium (v):
- n = c/v
The greater the refractive index, the more the light bends.

Snell's Law describes the relationship between the angle of incidence (θ1) and the angle of refraction (θ2) when light passes from one medium to another:
- n1 sin(θ1) = n2 sin(θ2)
n1 and n2 are the refractive indices of the first and second mediums, respectively.

Occurs when light travels from a denser medium to a rarer medium (n1 > n2) at an angle of incidence greater than the critical angle.
Light is reflected back into the denser medium instead of refracting out.
Used in optical fibers for high-speed data transmission.

Lenses: Transparent materials that refract light.
Converging Lens: Thick in the middle, converging light rays.
- Produce both real and virtual images.
- Form a real, inverted image when an object is beyond the focal point (F).
- Form a virtual, upright, and magnified image when an object is between the focal point (F) and the lens.
Diverging Lens: Thin in the middle, diverging light rays.
- Always produces virtual, upright, and smaller images.

The lens equation relates the object distance (do), image distance (di), and focal length (f) of a lens:
1/do + 1/di = 1/f
Convention:
- do is positive for real objects and negative for virtual objects.
- di is positive for real images and negative for virtual images.
- f is positive for converging lenses and negative for diverging lenses.

Cameras: Use lenses to focus light onto a light-sensitive sensor.
Telescopes: Use lenses or mirrors to gather light from distant objects and magnify them.
Microscopes: Use lenses to magnify small objects.
Eyeglasses: Use lenses to correct vision problems.
Fiber Optics: Use total internal reflection to transmit light signals over long distances.