Light and Optics

What is Light?

A particle.

Photons

Light particle, packet of waves.

The speed of light

300 million meters per second.

White Light

When all the colors of the rainbow are combined.

Cones

Respond to red, green, and blue.

Rods

Responds to black, white, and shades or gray.

Additive Primary Colors

Red, green, and blue

How we see the color of things.

The light can be emitted directly from the object, like a light bulb or glow stick. Or the light can come from somewhere else, like the sun, and we see the objects by reflected light.

Subtractive Primary Colors

Magenta, yellow, and cyan.

Why are plants green?

Plants absorb energy from light and convert it to chemical energy in the form of sugar.

Radio Waves

Used primarily for communication.

Microwaves

Cellphones, WiFi, RADAR, and Microwave ovens.

Cosmic Microwave Background

Left over radiation from the Big Bang is in Microwaves.

Infrared

Can be felt has heat, humans give off infrared radiation, used in remote controls and garage sensors.

UV-A

Indirect cell damage, black lights, gives you a tan, and causes skin to age and wrinkle.

UV-B

Indirect cell damage, gives you sunburns, can give you skin cancer, and helps you make vitamin D.

UV-C

Ionizing, blocked by the atmosphere, and used to kill bacteria.

Gamma Rays

Very dangerous in high doses, nuclear reactions, nuclear explosions, nuclear reactors, naturally occurring radioactive decays.

Real Image

Located where light rays come together, Can be projected on a screen, and positive image distance.

Virtual Image

Rays of light diverge, Image is at the position where the rays seem to be coming from, looks like it is behind the mirror, and negative image distance.

Upright

Image is right side up, positive magnification.

Inverted

Image is upside down, negative magnification.

Reduced Image

Smaller than the original, magnification < 1.

Enlarged Image

Larger than the original, magnification > 1.

Plane Mirrors

Flat, virtual image, same size, upright

Convex Mirror

Curves away on the outside, virtual images, used for security mirrors and in cars.

Concave Mirrors

Curves towards on the outside, real and virtual images, used as shaving and makeup mirrors.

Focal Length

Measures how well the mirror converges or diverges light.Concave = very far away.COnvex mirrors have negative focal length. Focal point is behind the mirror. Concave mirrors have a positive focal length. Focal point in front of the mirror.

Reflection

Law of reflection, the angle of reflection measured from the normal line equals the angle of incidence.

Diffuse

Eye sees reflected light at all angles.

Specular

Eye must be in the correct position.

Refraction

Bending og light as it moves from one medium to another. Occurs at the boundary between the two mediums.

Index of Refraction

Light slows down when it moves through a medium. Related to how much the light slows down. The more it changes speed the more it bends.

Snell’s Law

Refraction is what makes objects half-submerged in water look odd.

Total internal reflection

When angle is greater then or equal to the critical angle.

Diffraction

Light bends through small openings from diffraction.

Converging lens

Positive focal length, produces real or virtual images, used in magnifying class, reading glasses, camera lens, eye lense, and projector lens.

Diverging lens

Negative focal length, only produces virtual images, used in glasses and contacts.

Glasses

Lenses that correct for light focusing in front or behind the retina/.

Polarization

Light is polarized when its electric fields oscillate in a single plane, rather than in any direction perpendicular to the direction of propagation.