Light Waves

Light is energy. It has electric and magnetic fields, making it electromagnetic radiation. Light waves move as transverse waves at a speed of approximately 186,000 miles/second, which is much faster than sound. Light rays travel in a straight line and do not need a medium. A ray is a straight line that represents the path of light. A beam is a group of parallel rays. Wavelength and frequency definitions electromagnetic spectrum visible light reflection, refraction, transmitted, or absorbed as heat

Woah...it's really dark.

I'm kinda scared of the dark.

Can you please turn the lights on?

Ahhh...Much better! Thank you!

Light is pretty awesome. Let's learn about it.

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Let's zoom way out as we begin our exploration into light. Select Earth's ultimate source light in the model below.

A lot is going on inside that big ball of plasma and gas known as our sun!

Fusion reactions

Under A LOT of pressure, tiny particles fuse together to form bigger ones. What do you think is released as a result of these fusion reactions?

caffeine

energy

sugar

Yes! Fusion reactions in the sun release incredible amounts of energy.

A lot of this energy travels through space as light.

93 million miles

Note: This model is not to scale, not even close!

Select the ray that represents light traveling towards Earth.

Light travels about 93 million miles from the sun to Earth. It would take a car traveling at 100 miles per hour 100 years to travel 93 million miles.

Thankfully, light travels REALLY FAST at a speed of about 186,000 miles per second!

93 million miles

Note: This model is not to scale, not even close!

About how much time do you think it takes for sunlight to reach Earth?

8 seconds

8 minutes

8 hours

8 days

Yes! The journey of light energy from the sun to Earth takes approximately 8 minutes, during which it travels as an electromagnetic wave through the vacuum of space, without the need for any medium.

Select anywhere on the model of the electromagnetic wave above.

Of course our sun is not our only source of light. Other stars in the universe release light that we can see.

Select anywhere on the model of the electromagnetic wave above.

Light energy is emitted during some chemical reactions such as when wood burns or fireworks explode.

Select anywhere on the model of the electromagnetic wave above.

Light energy is emitted during some chemical reactions such as when wood burns or fireworks explode.

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Select anywhere on the model of the electromagnetic wave above.

Also, electrical energy is transformed into light and heat energy in the case of light bulbs.

Select anywhere on the model of the electromagnetic wave above.

Light travels in a straight line until it hits a new medium. Then, it can either be transmitted, absorbed, or reflected.

Select the diagram that represents light that is transmitted through a medium.

Yes! Transmitted light passes through the medium, such as air, water, or glass.

What is the path of light as it transmits through a medium?

Wiggly Line

Straight Line

Zig-Zag

You got it! Light travels in a straight line as it transmits through a medium.

Now, select the diagram that represents light that is absorbed by a medium.

When light is absorbed by a medium, its energy is converted into heat energy.

What happens to a black road as the sun shines on it?

It gets hotter.

It gets colder.

Nothing

Yes! When a medium, such as a road, absorbs sunlight energy, it gets hotter!

Now, select the diagram that represents light that is reflected by a medium.

Reflection occurs when light traveling through one medium bounces off a different medium. Most often, only some of the light is reflected. In the case of a mirror, almost all the light is reflected.

Select the image of the kitten that is formed as a result of the reflection of light.

Like all waves, electromagnetic light waves have properties that can be measured.

Today we will focus on the properties of wavelength, amplitude, and frequency.To understand each of these properties, we must first understand that the crest of a wave is the highest part of a wave and the trough of a wave is the lowest part of a wave.

Select one of the crests of the wave model above.

The wavelength of a wave is the distance between successive troughs, crests, or identical parts of a wave.

Select the image that shows the line that extends along one wavelength.

The amplitude of a wave is the distance from the center line to the top of a crest or to the bottom of a trough .

crest

center line

trough

Select the image that shows the line that represents the amplitude of a wave.

The frequency of a wave is a measure of how many waves pass a point in a certain amount of time.

One peak passes by the red dot per second. This measurement is the wave's frequency! The units are cycles per second, which is the same thing as Hertz.

This wave's frequency = 1 cycle/second = 1 Hertz

The units of frequency are Hertz. One Hertz is equal to __________.

1 cycle per second

1 cm/ second

1 centimeter

The wavelengths of light waves can be bigger than buildings or smaller than atoms.

Select the part of the electromagnetic spectrum diagram that shows the largest wavelengths and smallest frequencies.

Yes! Radio waves have the largest wavelengths and smallest frequencies.

Now select the part of the electromagnetic spectrum diagram that shows the smallest wavelengths and largest frequencies.

You got it! Gamma rays have the smallest wavelengths and highest frequencies.

Select the kind of electromagnetic waves that frequencies that humans can see as visible light.

Nice work! The sun emits waves from the entire electromagnetic spectrum. Only a tiny portion of the electromagnetic spectrum is visible light.

Select the rainbow of colors that represent the tiny portion of sunlight that humans can see.

Use this PhET simulation explore the different frequencies of visible light.

Play with the simulation for a bit. Be sure to push all the buttons and change the frequency and amplitude.

Now wait a second, the sun shines white light! Where are all the colors?

NASA.Mrshaba at en.wikipedia., Public domain, via Wikimedia Commons

Select the bright white sun to continue.

When all the colors of white light are combine, the light appears white. The colors can be seen when the the different wavelengths of visible light are separated, such as when a rainbow forms.

Select anywhere on the rainbow to learn how it forms.

Step 2The white light hits TRILLIONS of raindrops and refracts (bends) as it travels through the water of these raindrops. The red wavelengths refracts the most and the the blue refracts the least.

Step 4The light exits the raindrop and refracts again.

Step 1White light travels 93 million miles from the sun all the way into Earth's atmosphere.

Step 1White light travels 93 million miles from the sun all the way into Earth's atmosphere.

Step 5Humans see the white light that has been refracted, reflected, and refracted again as a rainbow!

Select the arrow that represents sunlight traveling through Earth's atmosphere.

Step 3The light reflects off the back inside of the raindrops.

Step 2The white light hits TRILLIONS of raindrops and refracts (bends) as it travels through the water of these raindrops. The red wavelengths refracts the most and the the blue refracts the least.

Step 4The light exits the raindrop and refracts again.

The blue wavelengths refract (bend) the most and the red wavelengths refract the least.The colors are now speparated!

Step 1White light travels 93 million miles from the sun all the way into Earth's atmosphere.

Step 2The white light hits TRILLIONS of water drops (such as raindrops or fog) and refracts (bends) as it changes medium from the air into the the water. Each color refracts by a different amount.

Step 5Humans see the white light that has been refracted, reflected, and refracted again as a rainbow!

Select the area in the model above that represents where light refracts as it changes medium from the air to the water within the raindrop.

Step 3The light reflects off the back inside of the raindrops.

Step 2The white light hits TRILLIONS of raindrops and refracts (bends) as it travels through the water of these raindrops. The red wavelengths refracts the most and the the blue refracts the least.

Step 4The light exits the raindrop and refracts again.

Step 1White light travels 93 million miles from the sun all the way into Earth's atmosphere.

Step 3The separated light reflects off the back inside of the raindrops.

Step 5Humans see the white light that has been refracted, reflected, and refracted again as a rainbow!

Select the area in the model above that represents where light reflects off the back side of the raindrop.

Step 3The light reflects off the back inside of the raindrops.

Step 2The white light hits TRILLIONS of raindrops and refracts (bends) as it travels through the water of these raindrops. The red wavelengths refracts the most and the the blue refracts the least.

Step 4The light exits the raindrop and refracts again.

Step 1White light travels 93 million miles from the sun all the way into Earth's atmosphere.

Step 4The light exits the raindrop and refracts again.

Step 5Humans see the white light that has been refracted, reflected, and refracted again as a rainbow!

Select the area in the model above that represents where the separated light refracts as it changes medium from the water to the air.

Step 3The light reflects off the back inside of the raindrops.

Step 2The white light hits TRILLIONS of raindrops and refracts (bends) as it travels through the water of these raindrops. The red wavelengths refracts the most and the the blue refracts the least.

Step 4The light exits the raindrop and refracts again.

Step 1White light travels 93 million miles from the sun all the way into Earth's atmosphere.

Step 5After being refracted, reflected, and refracted again by trillions of raindrops, the separated light travels down towards Earth where eyes can detect them and form the image of a rainbow!

Step 5Humans see the white light that has been refracted, reflected, and refracted again as a rainbow!

Fun fact:No two people see the same exact rainbow because each position on Earth receives light that has exited a different set of water drops!

About how many raindrops are needed to form the image of a giant rainbow in the sky?

hundreds of raindrops

trillions of raindrops

7 raindrops

Step 3The light reflects off the back inside of the raindrops.

Yes! Trillions of tiny water drops refract and reflect light to form the image of a rainbow.

Sometimes, the angle of the incoming light is just right to cause the light to reflect twice inside the raindrops. This results in a double rainbow! Select the model water drop that shows light that is reflected twice within it.

Our blue sky is another example of how white light separates! White light from the sun hits particles, such as nitrogen and oxygen gas molecules in the atmosphere.

White light from the sun hits the molecules in the atmosphere.

Select one of the arrows that represent white light from the sun.

The particles in the atmosphere reflect the blue and violet wavelengths much more than other wavelengths in white light.

White light from the sun hits the molecules in the atmosphere.

Select one of the arrows that represent light reflected off particles in the atmosphere.

The reflected blue and violet wavelengths of light are scattered in all directions, making the sky appear blue!

White light from the sun hits the molecules in the atmosphere.

Select the arrow that represents scattered blue light that the person sees.

Almost 80% of Greenland is covered by a giant sheet of ice.

As more CO2 and other greenhouse gases are added to the atmosphere, the Earth gets warmer. Evidence that the Earth is warming can clearly be seen in Greenland... WHERE THERE'S LOTS OF ICE!

Sunlight energy travels through mostly empty space in the form of electromagnetic radiation.

Note: This model is not to scale, not even close!

Which option describes the empty space between the sun and Earth?

Very Dark

Very Bright

That's right, almost all of space is... completely dark!

Once white sunlight hits the Earth's atmosphere, its beautiful colors can be seen.

Select the atmosphere.

White light from the sun hits tiny particles (such as nitrogen and oxygen molecules) in Earth's atmosphere.

White light from the sun hits the molecules in the atmosphere.

Select one of the particles in the atmosphere.

That's right, sunlight is not visible as it travels through empty space. But, its brightness and rainbow of colors can be seen when it reaches Earth!

Select the illumiated half of the Earth.

It takes sunlight about 8 minutes to make that 93 million mile journey all the way to Earth.

White light from the sun hits the molecules in the atmosphere.

When the white light, made up of all the colors of light, hits the particles in the atmosphere the shorter wavelengths scatter (hit the particles and get re-emited in a random direction) more than the other wavelengths.

Blue wavelengths of light are scattered in all directions through the atmosphere.

Nope! If that were true, why would the sky be blue here?

So the sky is not reflecting blue from the ocean?

Sunlight can appear a very light yellow because it's missing the wavelengths that were scattered.

Continue

Click on the sun to see what it looks like from outside Earth's atmosphere.

Let's figure out this whole light thing. I have an idea! Let's use a PhET simulation to learn about light.

Play with the simulation for a bit. Be sure to push all the buttons and change the frequency and amplitude.

Click on the ultimate source of energy for life.

What is light?