Light

What is light? Light is a form of an electromagnetic wave. Recall: a wave is one method of transferring energy (the other is using matter)

How is light produced? Light is produced as energized electrons drop into a lower energy level. Electrons become energized as they absorb chemical, heat, electrical, or nuclear energy.

Incandescent Bulbs A bulb that produces light when a filament is heated. Much of the energy used to excite the filament atoms is given off as heat; therefore, incandescent bulbs are not efficient.

Fluorescent Bulbs UV energy is transmitted through a bulb coated with phosphorus. After the phosphorus absorbs the energy, it emits visible light. Very little energy is converted to heat energy using a fluorescent bulb.

L.E.D. Lighting Light Emitting Diode- source of light produced as electrical energy travels through a specially charged semi-conductor.

Electromagnetic Spectrum The entire range of energy emitted as electrons drop back into a non-energized level. Radiowaves, Microwaves, Infra-red, Visible, Ultra-violet, X-ray, Gamma ray

EM Spectrum Energy The amount of energy given off varies based on the energy absorbed by an electron and the beginning energy level of the electron.

EM Uses Radio wave: transmit radio signals, astronomy Microwave: cooking, cell phone transmission, astronomy Infra-red: thermal radiation (heat); astronomy Visible: COLORS

EM Uses part 2 Ultra-violet: sunburn, astronomy X-ray: medical, research, astronomy Gamma: cancer therapy, astronomy

COLORS

COLORS part 2 All of the colors in the rainbow are really light of different energies of the EM spectrum. Low energy  Red Light High energy  Blue Light All energies  White Light No energy  Black Light

How do we see COLORS? Light energy must reflect back to our eye with the color we hope to see. If an object absorbs a color, all the colors but the absorbed color is reflected back to one’s eye. Blue Green Red Magenta Cyan Yellow White

Polarized Light Because EM waves are transverse waves composed of an electrical and a magnetic function perpendicular to each other.

Polarized Products Sunglasses are often polarized to reduce glare off water, snow, and roads. Polarized films are also used to make LCD screens.

Ch 14 Book Problems Concept Review Problems 3, 6, 7, 8, 9, 10, 11 5, 6, 10, 11

Refraction of Light Light bends as it passes from one medium into another. The difference in optical densities determines how much the light bends. Light will bend more going from air into glass than from air into water.

Lens

Focal Point

Optical Technology The angle of incidence of the light is greater than a critical angle, so that all of the light is reflected back inside a medium instead of refracting out of the material. This is called total internal reflection.

Ch. 15 Book Problems Concept Review 3, 13 Problem 2, 3, 4,