Light Light

Light is a form of energy called radiant energy

This energy travels to Earth in a vacuum of space. 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! A wave is energy that moves through a 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?

Frequency Wavelength Amplitude 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 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 Red Orange Yellow Green Blue Indigo Violet

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

refraction 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.

Opaque No light passes through Example – wood, foil, 50 sheets of paper

Allows all light rays to pass through Example - glass, shallow water Transparent Allows all light rays to pass through Example - glass, shallow water

Allows some light rays to pass through Translucent 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.

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 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?