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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
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 energycan cause changes in matter The light energy is changed to other forms of energyFor 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.
Photons! Tiny invisible particles of energy! Photons are energy, not matter, so no weight!
So, how does light travel?
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 isCrest – highest point of the waveTrough – lowest part of the wave
Hmmm.. Does this sound familiar?
Who remembers waves from our ocean unit?
Light Waves are measured according to:
Frequency the number of waves that pass a point in a specific amount of
time (like a second)
Wavelength measurement from the crest of one wave to another crest
Amplitude 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 LightWhat 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 spectrumRedOrangeYellowGreenBlueIndigoViolet
ROYGBIV The visible light spectrum
Red – Orange – Yellow – Green – Blue – Indigo - Violet
Reflection 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?
Refraction
the bending &
slowing down of
light waves
A prism works like a rainbow!It separates white light into the spectrum known as
ROY G BIV. When light passes into the prism glass it slows down and bends. This is known as
refraction
Rainbows are produced when white light strikes drops of water. Each drop acts like a prism that separates the white light into
ROYGBIV.
OpaqueNo light passes through
Example – wood, foil, 50 sheets of paper
Transparent Allows all light rays to pass through
Example - glass, shallow water
Translucent Allows some light rays to pass through
Example: wax paper – one piece of paper
Light Activity
1. Each table will have one container of objects.2. Experiment with the prism to find ROYGBIV3. Experiment with the disk to find ROYGBIV4. Answer questions on the ROYGBIV worksheet
5. Find your What’s Blocking the Light worksheets in packet6. Choose an object such as a pencil or eraser. 7. Now take a material that you believe is transparent from8. Your box of goodies. 9. Observe what happens when you place it over the object you 10.have chosen.11.Draw in the cloud what you observe.12.Write about what you observe13.Do the same for translucent and opaque14.When finished, try experimenting with other materials in box15.Fill in boxes with materials that are transparent, translucent and opaque16.Finish worksheet.
Refraction
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 LensA lens that is wider at the edges than in the middle, and
That refracts light rays so they bend outward
Convex LensA 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 camerasThe pupil is the opening
Iris – controls the amount of light that enters the eyeRetina – 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?