Let there be light!!!

Light Energy &How light interacts with matter

What is light?

• Light is a form of radiant energy that you can detect with your eyes. Light energy comes from chemical energy, electrical energy and nuclear energy.

• Light can pass through anything that is transparent, sort of passes through translucent objects (frosted window) but doesn't make it through opaque objects such as a brick wall.

Properties of Light

•Light travels in straight lines:

Laser

Light travels VERY FAST – around 300,000 kilometres per second.

At this speed it can go around the world 8 times in one second.

• Light travels much faster than sound. For example:

Thunder and lightning start at the same time, but we will see the lightning first.

We see things because they reflect light into our eyes:

Homework

Luminous and non-luminous objects

A luminous object is one that produces light.

A non-luminous object is one that reflects light.

Luminous objects

Reflectors

•Sun

•Light bulbs

•Fire

•Water

•Mirrors

•Smooth shiny surfaces

Shadows

Shadows are places where light is “blocked”:

Rays of light

Properties of Light summary

1) Light travels in straight lines2) Light travels much faster than

sound3) We see things because they

reflect light into our eyes4) Shadows are formed when light is

blocked by an object

Reflection• Reflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

•The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

In other words, light gets reflected from a surface at ____ _____ angle it hits it.

The same !

!!

Clear vs. Diffuse Reflection

• Smooth, shiny surfaces have a clear reflection:

Rough, dull surfaces have a diffuse reflection.

Diffuse reflection is when light is scattered in different directions

Using mirrors• Two examples:

1) A periscope

2) A car headlight

Color• White light is not a single color;

it is made up of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light with a prism:

This is how rainbows are formed: sunlight is “split up” by raindrops.

• A rainbow would form a complete circle, not just an arc, if the ground didn't get in the way

• Rainbows always face the observer.  As the observer moves, the rainbow moves.

• And sorry, no one can ever get to the "pot of gold" at the end of the rainbow

Seeing color• The color an object appears depends on

the colors of light it reflects.

For example, a red book only reflects red light:

White

light

Only red light is

reflected

A white hat would reflect all seven colors:

A pair of purple shorts would reflect purple light (and red and blue, as purple is made up of red and

blue):

Purple light

White

light

Take a ride on the Magic School Bus!

RefractionRefraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a ruler is placed in water it looks like this:

In this case the light rays are slowed down by the water and are _____, causing the ruler to look odd. The two mediums in this example are ______ and _______.

Words – speed up, direction, water, air, bent

Key Vocabulary

Reflection – The light energy that bounces off objects.

Refraction – The bending of light rays when they pass through a substance.

Convex and Concave Mirrors

Images in convex mirrors          Images in concave mirrors are always smaller. are always bigger.

Convex and Concave Lenses

• Convex Lenses  are used as a Magnifier

• Concave Lenses  are used as a De-magnifier

Convex Lenses• People who are farsighted

have trouble seeing things that are close to them (reading) Glasses or contacts with convex lenses magnify the print

• Movie projectors use convex lenses. As light from the bulb shines through the film, light rays spread apart. As these rays pass through the projector lens, they bend toward each other again.

Concave Lenses• Concave lenses help

people who are nearsighted. These people have trouble seeing distant objects. Concave lenses bend light rays outward just enough to make distant objects seem closer.

• Some cameras have a concave lens in their viewfinder, you see a small version of what the final photograph wil look like.

Key Vocabulary

lens – a piece of clear material that bends, or refracts, light rays passing through it.

Convex lens – is thicker in the middle than at the edges.

Concave lens – is thicker at the edges than in the middle.

Using Light, Lenses, and Mirrors for space

exploration

In Galileo's version, light

entering the far end (1) passed through a convex lens (2), which bent the light rays until they came into focus at the focal point (f). The eyepiece (3) then spread out (magnified) the light so that it covered a large portion the viewer's retina and thus made the image appear larger.

Refracting Telescope

Reflecting Telescope

In Newton's version, light streaming in one end (1) reflected off a concave mirror fixed inside the other end (2), then off a flat mirror set an angle (3). The light came into focus at the focal point (f) and then was magnified for the viewer by the eyepiece (4).

Take a ride on the Magic School Bus!