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Light - PowerPoint PPT Presentation

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Light. Light. Light is a form of energy called radiant energy. The Sun gives off huge amounts of energy called electromagnetic radiation or radiant energy. This energy travels to Earth in a vacuum of space. . Some of this E-M or radiant energy you can see some you can’t

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Light is a form of energy called radiant energy

The Sun gives off huge amounts of energy called electromagnetic radiation or radiant energy.

This energy travels to Earth in a vacuum of space.

  • Some of this E-M or

  • radiant energy

  • you can see

  • some you can’t

  • Visible light you can see!

  • Hence the word visible!

  • Most types of E-M or radiant energy are invisible.

  • For example:

  • Infrared radiation

  • Ultraviolet radiation (ouch!)

  • X-rays

  • Microwaves

  • Radio waves

  • Gamma rays

Light starts many chemical

reactions such as photosynthesis

Radiant energy

can cause changes in matter The light energy is changed

to other forms of energy

For example:

Sunlight heats the

water in the ocean

What about

solar power?

Is this a change in the form of energy?

Remember chemical reactions?

Many give off light.

So, how does light travel?

Photons! Tiny invisible particles of energy!

Photons are energy, not matter, so no weight!

Wow, I am as light as a photon!

But, I still don’t get it!

How do the photons get to where they are going?

Light moves in waves!

No, not those waves!

Light Waves like this!

Geez! Do I always have to tell you guys everything?

A wave is energy that moves through a

medium (solid, liquid, or gas)

But however they travel…..

light waves all travel through space at the same speed and they can all travel through a vacuum.

Nothing is a fast as the speed of light….well almost nothing!

It travels 300,000 km/s!

That’s fast!

Light could travel around the world 7.5 times in 1 second!

Waves – light waves that is

Crest – highest point of the wave

Trough – lowest part of the wave

Hmmm.. Does this sound familiar?

Who remembers waves from our ocean unit?

Light Waves are measured according to:


the number of waves that pass a point in a specific amount of time (like a second)


measurement from the crest of one wave to another crest


measurement from crest to the midline, or crest to trough

divided by two

High frequency wave= short wave length =

more energy

Low frequency waves =

longer wave length =

less energy

How Light Behaves

“Light”, the dog

Light behaves in different ways when it strikes different things

Light slows down - bends – or bounces back when it travels through different mediums like gas, liquids, or solids

We’ll learn in the next unit that sound is just the opposite!

Sound waves speed up when they travel through

different mediums such as gas, liquids, or solids.

Visible Light

What we see is white light

that is actually made up of many colors of light

We can only see

these colors when

they are

reflected or refracted

ROYGBIV – the visible light spectrum








ROYGBIV The visible light spectrum

Red – Orange – Yellow – Green – Blue – Indigo - Violet


the return of light or sound as it bounces off a surface

Reflection is the way we see most things!

The colors of light that an object reflects are the colors we see.

For example: an apple absorbs most of the sunlight that strikes it.

The rest of the light – the red part – reflects off the apple.

That’s why the apple appears red to us.

Cool heh?


the bending


slowing down of

light waves

A prism works like a rainbow!

It separates white light into the spectrum known as


  When light passes into the prism glass it slows down and bends. This is known as


Rainbows are produced when white light strikes drops of water.

Each drop acts like a prism that separates the white light into



No light passes through

Example – wood, foil, 50 sheets of paper


Allows all light rays to pass through

Example - glass, shallow water


Allows some light rays to pass through

Example: wax paper – one piece of paper

Light Activity

Each table will have one container of objects.

Experiment with the prism to find ROYGBIV

Experiment with the disk to find ROYGBIV

Answer questions on the ROYGBIV worksheet

Find your What’s Blocking the Light worksheets in packet

Choose an object such as a pencil or eraser.

Now take a material that you believe is transparent from

Your box of goodies.

Observe what happens when you place it over the object you

have chosen.

Draw in the cloud what you observe.

Write about what you observe

Do the same for translucent and opaque

When finished, try experimenting with other materials in box

Fill in boxes with materials that are transparent, translucent and opaque

Finish worksheet.


the bending & slowing down of light waves when they pass from one kind of matter to another

A mirage is an example of light refraction.

The difference in air temperature bends the light

Concave Lens

A lens that is wider at the edges than in the middle, and

That refracts light rays so they bend outward

Convex Lens

A lens that is wider in the middle than it is at the edges

It refracts light rays so they come together.

Nearsighted means you can see

close up, but not far away.

Concave lenses correct nearsighted vision.

Farsighted means you can see faraway objects,

but not close up objects.

Convex lenses correct farsighted vision

Other examples of convex lenses are:

magnifying glasses, telescopes, microscopes, & binoculars

How do we see?

Our eyes are like cameras

The pupil is the opening

Iris – controls the amount of light that enters the eye

Retina – a layer of light sensitive cells at the back of the eye

The retina sends a signal to our brain to tell us what we are seeing

Hey can someone turn off the light?

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