Reflection, Refraction,and Absorption

Light travels in a straight line. What happens when it hits an object???

It can bounce back (reflect), bend (refract), or be absorbed (absorb) by the object.

Reflection• Reflection occurs when an

object or wave bounces back off a surface through which it can not pass.• What sort of objects reflect

light?• Mirrors• Shiny surfaces• Some metal• Surface of water

Law of reflection The law of reflection states

the angle of incidence equals the angle of reflection.

The angle of incidence (angle of the incoming wave) is the same as the angle of reflection (angle of the reflected wave).

Notice on the diagram to the left how on a smooth surface, the light bounces back at the same angle it hits the surface.

Plane Mirrors Plane mirrors- A flat sheet

of glass with a silver coating on one side. When light strikes the coating the image and the light is reflected back.

The image produced is a virtual image, which is upright and reversed

Concave Mirrors Concave Mirror: A mirror with a surface that

curves inward. (Think “cave”) Example: makeup mirrors (they enlarge the image), inside

of a spoon. This gives these mirrors the ability to create an

image when their curvature bounces light to a specific area in front of them. This area is called the focal point.

From far away, objects will seem upside down, but as you get closer and pass the focal point, the image flips and magnifies.

Concave Mirrors Reflecting telescopes

use a concave mirror instead of an objective lens to gather light from a distant object. Used by astronomers Invented in the 1600s

Convex Mirror• Convex Mirror: A mirror with a

surface which curves outward.• This gives a wide field of view

and is used in security mirrors in stores as well as side mirrors on cars.

• The image in a convex mirror is always upright and is smaller than the object.

Convex Mirror

Refraction• When light waves bend when

passing through one substance to another, this is refraction.• When light rays enter a medium at

an angle, the change in speed causes the light rays to bend, or change direction.• What sort of objects refract

light?• Prisms• Cut diamonds• Water• Soap bubbles• Microscope lenses

Absorption• When light is absorbed by an object this is usually when

light transfers its energy into another form (like heat). • Have you ever worn a black shirt on a sunny day? What

happens? Do you feel the light energy turn into heat?

What sort of objects absorb light?

Technically most items do absorb some light. In fact, the color does matter! When we see an object that is green that is because the object is absorbing all of the colors EXCEPT for green. Green is bounced back to our eye and we see a green object.

How does a rainbow form?

First, what things are

needed for a rainbow to

form?

Refraction = Waves changing direction as they travel from one material to another.

Mini-Lab: Refraction in Water

Viewing from the side, draw picture of pen/pencil in empty beaker. Then add water and draw again.

Why does the pencil bend in the water?

Refraction! Light waves travel at DIFFERENT SPEEDS through air and water.

So waves travel at different speeds through air and water

.......and rainbows need light and rain...so....

Rainbows form when light is refracted off raindrops. If the sun is at the correct angle, different drops will refract different colors.