Light and Optics

Physical Science 92 B

Reference: Ch 14 & 15

LightWe see objects because of their reflected light.

Can carry heat

Travels far and fast

Travels in a straight line unless bent or reflected.

Can carry color.

What makes light?Almost everything that creates light is made of atoms.

Elements have electrons which are in shells.

The further from the nucleus, the more energy it has.

As it falls to a lower level, emits energy.

Visible Light and UVROY G. BIV-colors of visible light.

Sunlight emits UV along with other rays.

Gives us Vitamin D

Too much harmful.

Most filtered by ozone.

Speed of LightSpeed of sound-340 m/s

Speed of light-300 million m/s

Einstein figured out how light behaved

PolarizationRays are all vibrating on the same plane.

A polarizer allows only 1 type through. Ex: sunglasses.

Many things use polarized light-laptop monitors

ColorColor has freq and wavelength

One goes up, the other goes down.

Red-longest wavelength, lowest freq

Violet-shortest wavelength, highest freq

How do I see color?Photochemical receptors receive the light (rods and cones)

They release a chemical signal to the brain.

Brain interprets the signal

Rods-brightness, cones-the color

Primary colors of light: red, blue, green mix together to make white.

Additive and subtractivePrimary colors of light are additive-each one adds more light and the result is white.

Primary pigment colors are subtractive-each one takes away more light and the result is black. (magenta, cyan, yellow)

Optics and Reflection• Optics-the study of

how light behaves • Deals with the

collection and use of light to create images

• Includes: lenses, mirrors, and prisms

• Law of reflection: determines the reflected ray

• Light rays bounce off a mirror at the same angle at which they arrive

• We always define angles relative to the normal (the line perpendicular to the mirror (or lens)

Mirrors & Prisms

• Mirrors reflect light– Flat mirrors show true-size

– Curved mirrors cause light to come together or spread apart

• Prisms cause light to change directions– Traditionally used to separate the

colors of light and to show how light bends

Images

• Objects are any real physical things that gives off or reflects light

• Images are “pictures” of objects formed where light rays from the object meet

• Normally light travels in straight lines

• To make images, sometimes light must be bent between an object and your eye

Reflection & Mirrors

• A mirror reflects rays of light so that they change their path

• Mirrors create a virtual image– Image appears behind the mirror and is reversed– The light rays are reflected back to your eye at an

equal but opposite angle

• Incident ray – the ray that comes from the object and hits the mirror

• Reflected ray – the ray that bounces off the mirror

Refraction and Lenses • A lens uses refraction to cause light to

come together or spread apart• Refraction – The bending of light that

occurs when light crosses a boundary between two different substances– EX. Glass, Plastic, Water

• Lens – a shape of transparent material that is used to bend the light rays– Shape is determined by how strong we bend

the light