UNIT EIGHT: Waves



Chapter 24 Waves and Sound



Chapter 25 Light and Optics

Chapter Twenty-Five: Light and Optics



25.1 Properties of Light



25.2 Color and Vision



25.3 Optics

Chapter 25.3 Learning Goals



Explain how basic optical devices function.



Compare and contrast the interactions of light and matter.



Distinguish between concave and convex lenses.

Investigation 25B

Reflection and Refraction 

Key Question:

How does light behave when its path is changed?

25.3 Basic optical devices Three useful optical devices are: 1.

lenses 2.

3.

mirrors prisms

25.3 Basic optical devices



A

converging lens

bends light so that the light rays come together in a point.



This is why a magnifying glass makes a hot spot of concentrated light.



A

mirror

and allows you to see yourself.

reflects light

25.3 Basic optical devices



A

mirror

reflects light and allows you to see yourself.

25.3 Basic optical devices



A

prism

light. , usually a solid piece of glass with flat polished surfaces, can both bend and reflect



Telescopes, cameras, and laser scanners use prisms.

25.3 Ways that light is affected by matter



When light interacts with matter, it can:

    pass through almost unchanged (be transparent) pass through but is scattered (be translucent) bounces off (be reflected) transfers its energy (be absorbed)

25.3 Ways that light is affected by matter



All four interactions almost always happen together.



The green shirt absorbs some light, reflects some light, and is partly translucent.

Can you tell which colors are reflected and which are absorbed?

25.3 Light rays



Reflection

occurs when light bounces off a surface and when light bends while crossing through materials.

25.3 Refraction



When light rays travel from air to water, they

refract

.



This is why a straw in a glass of water looks broken or bent at the water’s surface.

25.3 Law of reflection



The

law of reflection

states that the angle of incidence is equal to the angle of reflection.

25.3 Reflection



Not all reflections form images.



Rays light that strikes a shiny surface (like a mirror) create

specular reflection

.



Light rays reflected at different angles from dull or unven surfaces cause

difuse reflection.

25.3 Refraction



Materials with a higher

index of refraction

light by a large angle. bend



The index of refraction for air is about 1.00.



Water has an index of refraction of 1.33.

25.3 Refraction



Vegetable oil and glass have almost the same index of refraction.



If you put a glass rod into a glass cup containing vegetable oil, the rod disappears because light is NOT refracted!

25.3 Lenses



An ordinary

lens

is a polished, transparent disc, usually made of glass.



The shape of a converging lens is described as being “

convex

” because the surfaces curve outward.

25.3 Lenses



The distance from the center of the lens to the focal point is the

focal length .



Light can go through a lens in either direction so there are always two focal points, one on either side of the lens.

25.3 Lenses



For a

converging lens

, the first surface (air to glass) bends light rays toward the normal.



At the second surface (glass to air), the rays bend away from the normal line.

25.3 Lenses



A

diverging lens

has concave surfaces.



For a diverging lens, you can show the focal point in a diagram by extending the path of the exiting light rays back through the lens.

Bioluminescence- Glow Live!



Like a glow stick, living things produce their own light using a chemical reaction. Bioluminescence is “cold light” because it doesn’t produce a lot of heat. While it takes a lot of energy for a living thing to produce light, almost 100 percent of the energy becomes visible light.