Unit C Lesson C6 Refraction and the Speed of Light
Completion requirements
Lesson C6: Refraction and the Speed of Light
Video Lesson
Why do objects viewed through water sometimes form strange images? How does Earth's atmosphere play tricks with light? Watch this video to learn more about how light bends in the process of refraction.
Lesson C6: Refraction and the Speed of Light
Figure C.2.6.1 – Sundogs sometimes form in cold weather.
Figure C.2.6.2– Sundogs are a result of refraction.
Figure C.2.6.3– Sundogs can also appear in warmer, more southerly locations.
Reading and Materials
for This Lesson
Science in Action 8
Reading: Pages 200–203
Materials:
Small coin (like a nickel or dime), clear drinking glass, small piece of cardboard (must completely cover top of glass), water, laser pointer, empty and clean 2-litre plastic pop bottle, sharp screwdriver, duct tape, large shallow pan, flat-bottomed
pot, flashlight, mirror, white paper.
Sundogs
Sometimes two bright spots form on either side of the sun. These bright spots are called sundogs. They form when the sun is very low on the horizon. Sundogs tend to occur in cold weather, due to ice crystals in the atmosphere. Light from the sun enters the ice crystals. Since ice is more dense than air, the light bends. The refracted light forms bright sundogs and sometimes a halo around the sun.
Sometimes two bright spots form on either side of the sun. These bright spots are called sundogs. They form when the sun is very low on the horizon. Sundogs tend to occur in cold weather, due to ice crystals in the atmosphere. Light from the sun enters the ice crystals. Since ice is more dense than air, the light bends. The refracted light forms bright sundogs and sometimes a halo around the sun.
Watch More
Sundogs in the Sky
Watch this video to learn more about how sundogs are caused by light refraction in ice crystals.
Watch this video to learn more about how sundogs are caused by light refraction in ice crystals.
Lesson Activity
Problem:
Try this online simulation to explore how light bends in different substances.
Download:
DOWNLOAD this document. It
provides a space for you to write your analysis questions later in this activity. It also provides tables for you to record your observations.
Instructions:
- Click here to open the refraction simulation.
- Play with the simulation to see what happens when you change different parts of the simulation. Drag the “source angle” slider back and forth. Click the buttons for different substances. Click the “swap ray direction” button.
Figure C.2.6.4– Step 3; source angle set to 5°, refraction of light from air to diamond.
Figure C.2.6.5– Step 4; refracted angle of 10°, refraction of light from air to water.
- Make sure the “swap ray direction” button is off. Set the source angle to 5° (see figure C.2.6.4). Click through each of the substances to observe the refracted angle. Record your observations in the table in the document you downloaded. Repeat
for source angles of 30° and 60°.
- Make sure the “swap ray direction” button is off. Select air as the refraction substance. Adjust the source angle to create a refracted angle of 10° (see figure C.2.6.5). Record the corresponding source angle in the table in the document you downloaded.
Repeat for refracted angles for 20° and 30°. Repeat for all the other substances.
Figure C.2.6.6– Step 5; swap direction, source angle of 5°, refraction of light from glass to water.
Figure C.2.6.7– Step 6; swap direction, refracted angle of 20° in air from diamond.
- Turn the “swap ray direction” button on. Set the source angle to 5° (see figure C.2.6.6). Click through each of the substances to observe the refracted angle. Record your observations in the table in the document you downloaded. Repeat for source
angles of 20°, 30°, and 60°.
- Make sure the “swap ray direction” button is on. Select air as the source angle substance. Adjust the source angle to create a refracted angle of 20° (see figure C.2.6.7). Record the corresponding source angle in the table in the document you downloaded.
Repeat for refracted angles of 50° and 70°. Repeat for all the other substances.
- Simulate light entering and exiting a glass windowpane.
- Turn the “swap ray direction” button off. Select glass as the substance. Set the source angle in air to 50°. What is the refracted angle of light in glass?
- Turn the “swap ray direction” button on. Adjust the source angle to the same refracted angle of light in glass in Part A. What do you observe about the refracted angle of light back into air?
Analysis Questions:
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.
When light travels from less dense air into a more dense substance, the refracted angle of light becomes smaller than the source angle of light.
Diamond bends light the most because diamond is the most dense substance. As light travels from air into diamond, the dense particles in diamond cause light to slow down and bend. Air bends light the least. When light travels into the same substance,
it does not bend.
Light refracted a smaller amount at smaller source angles. Light refracted a larger amount at larger source angles.
When light travels from a more dense substance into less dense air, the refracted angle of light becomes larger than the source angle of light.
Light travelling from diamond into air bends the most, because light speeds up the most as it travels from the dense diamond into less dense air. Light did not bend when it travelled from air back into the identical substance of air.
As the source angle of light increases in a dense substance, its refracted angle approaches 90 degrees. At a certain source angle for each substance, the light cannot be refracted greater than 90 degrees, and so instead, the light internally
reflects back into the substance.
When light travels from air into glass, it bends into a smaller angle. When light exits glass back into air, it bends back into its larger original angle. Light rays travelling out of glass are parallel to light rays entering the glass, enabling
us to see objects clearly.
Try It!
Vanishing Coin Trick
Try this simple experiment to make a coin disappear from sight!
Materials:
Try this simple experiment to make a coin disappear from sight!
Materials:
- Small coin (like a nickel or dime)
- Clear drinking glass
- Small piece of cardboard (must completely cover top of glass)
- Water
Instructions:
Part 1
Part 2
Watch the following video to see what happens if the penny gets wet.
Part 1
- Place the coin on a flat surface.
- Place the bottom of the glass over the coin.
- Cover the top of the glass with the piece of cardboard.
- Look through the side of the glass. Can you see the coin?
- Remove the piece of cardboard and fill the glass with water.
- Put the glass back on top of the coin.
- Cover the top of the glass with the piece of cardboard.
- Look through the side of the glass. Can you see the coin?
Part 2
Watch the following video to see what happens if the penny gets wet.
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
For you to see the coin, light rays must travel from the coin to your eyes. When the glass was filled with air, light rays passed through air and glass to reach your eye. The air did not refract or bend the light very much because it has a low
density. The thin denser glass only refracted light rays a small amount, so they could still reach your eye. There is even a thin layer of air under the beaker, between the coin and the glass, which adds another refraction of the light. Therefore,
the light bouncing off the coin has a path of coin -> air -> glass -> air -> glass -> air.
However, when the glass was filled with water, light rays passed through both water and glass to reach your eye. Water is denser than air, so it refracted light rays a larger amount. The light bouncing off the coin has a path of coin -> air -> glass -> water -> glass -> air. The water and glass refracted light from the coin so much that light rays could not exit the side of the glass, which is why you could not see the coin.
However, when the glass was filled with water, light rays passed through both water and glass to reach your eye. Water is denser than air, so it refracted light rays a larger amount. The light bouncing off the coin has a path of coin -> air -> glass -> water -> glass -> air. The water and glass refracted light from the coin so much that light rays could not exit the side of the glass, which is why you could not see the coin.
Covering the top of the glass with cardboard for both observations made it a fair test between the glass filled with air and the glass filled with water. You could not see any images coming out the top of the glass, which might have influenced
your observations.
The coin underwater has to reflect light to our eyes in order to be seen. The light only has to travel through the water, then the beaker, to reach the air where our eyes are. The light is refracted, but not enough to block it from reaching
our eyes.
The wet coin changes the path of the light from the coin to our eyes. The path, starting at the coin, is coin -> water -> glass -> water -> glass -> air. There is no large refraction from air to glass like there is when the coin
is dry, so we can still see the coin.
Figure C.2.6.8– Internal reflection occurs because light cannot be refracted greater than 90 degrees.
Figure C.2.6.9– Internal reflection occurs inside fibre optic cables.
Figure C.2.6.10– Notice the image of the underwater swimmer where water meets the air. This is internal reflection.
Internal Reflection
Although we usually think of reflected light as travelling through air and bouncing off a surface, sometimes light reflects inside of liquids or solids. We describe this as internal reflection. Glass fiber optic cables and sparkling diamonds show internal reflection.
Internal reflection can happen when light travels from a more dense substance to a less dense substance. Light cannot refract at angles greater than 90 degrees. Each substance has a specific source angle, called the critical angle, where the light cannot refract as it exits the substance. Instead, light reflects back into the substance. Internally reflected light follows the Law of Reflection. The source angle is the same as the internally reflected angle.
Although we usually think of reflected light as travelling through air and bouncing off a surface, sometimes light reflects inside of liquids or solids. We describe this as internal reflection. Glass fiber optic cables and sparkling diamonds show internal reflection.
Internal reflection can happen when light travels from a more dense substance to a less dense substance. Light cannot refract at angles greater than 90 degrees. Each substance has a specific source angle, called the critical angle, where the light cannot refract as it exits the substance. Instead, light reflects back into the substance. Internally reflected light follows the Law of Reflection. The source angle is the same as the internally reflected angle.
Try It!
Light Stream
Try this simple experiment to observe the internal reflection of light in water.
Materials:
Try this simple experiment to observe the internal reflection of light in water.
Materials:
- Laser pointer
- Empty and clean 2-litre plastic pop bottle
- Sharp screwdriver
- Water
- Duct tape
- Large shallow pan
- Flat-bottomed pot
Safety Warning
This activity involves several items that can hurt you, if they are not used carefully.
This activity must be completed with the supervision and assistance of an adult. DO NOT attempt this activity by yourself.
Take care with sharp objects; don’t cut yourself or anyone else!
Laser pointers can damage eyes. Never look directly into a laser pointer and never point a laser pointer directly into anyone else’s eyes.
This activity must be completed with the supervision and assistance of an adult. DO NOT attempt this activity by yourself.
Take care with sharp objects; don’t cut yourself or anyone else!
Laser pointers can damage eyes. Never look directly into a laser pointer and never point a laser pointer directly into anyone else’s eyes.
Instructions:
- With the screwdriver, poke a small hole in the side of the plastic bottle. The hole should be located one-third of the way up from the bottle’s bottom.
- Cover the hole with a piece of duct tape.
- Completely fill the bottle with water.
- Turn the flat-bottomed pot upside down on a flat surface.
- Place the large shallow pan next to the pot.
- Put the pop bottle on top of the pot. Arrange the bottle so that its hole is facing the large shallow pan.
- Turn off most lights in the room. For safety, you should leave the door open a crack or turn a flashlight on, so that you can see what you are doing.
- Take the duct tape off the hole. Quickly adjust the shallow pan if necessary, to catch the stream of water. Immediately aim the laser pointer at the hole, from the other side of the bottle.
- What do you observe?
- Watch this video to see this experiment and its results:
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Light from the laser pointer entered the water. It travelled into the water stream at a very large angle, nearly horizontally. At this large angle of nearly 90 degrees, light could not bend and exit into the surrounding air. Instead, it internally
reflected in the water. The process of internal reflection caused light to travel down the stream of water.
Fibre optic cables work in a similar way to this experiment. Light entering glass fiber optic tubes at a large angle cannot exit back into air. Instead, light internally reflects down the glass fiber optic tube.
Figure C.2.6.11– Diamonds sparkle due to refracted and reflected light.
Figure C.2.6.12 – The shape of a cut diamond causes the internal reflection of light.
Figure C.2.6.13– Uncut diamonds do not refract and reflect as much light as cut diamonds.
Sparkly Diamonds
People like how diamonds sparkle in the light, which is why they are used in jewelry. However, most raw diamonds mined from the ground don’t sparkle. Diamonds must be cut into shapes with many flat faces, or facets, in order to sparkle.
Diamond is a material that bends light rays at a large angle. As a result, light internally reflects off the inner surfaces of a cut diamond. The many facets of a diamond provide many surfaces for light reflection. Light rays eventually exit the diamond at many different angles. These reflected light rays give a diamond its sparkly appearance.
People like how diamonds sparkle in the light, which is why they are used in jewelry. However, most raw diamonds mined from the ground don’t sparkle. Diamonds must be cut into shapes with many flat faces, or facets, in order to sparkle.
Diamond is a material that bends light rays at a large angle. As a result, light internally reflects off the inner surfaces of a cut diamond. The many facets of a diamond provide many surfaces for light reflection. Light rays eventually exit the diamond at many different angles. These reflected light rays give a diamond its sparkly appearance.
Watch More
The Amazing Diamond Cutters
This video explains how diamonds are cut to make them sparkle.
This video explains how diamonds are cut to make them sparkle.
Figure C.2.6.14– Rainbows form when light refracts in atmospheric water droplets.
Figure C.2.6.15– Rainbows often appear in the spray from waterfalls.
Figure C.2.6.16– A double rainbow forms when light internally reflects twice inside a water droplet.
Rainbows and Refraction
When white light enters and leaves a substance at an angle, it splits into its different colours. For example, when white light enters a glass prism at an angle, the light splits into its component colours when it exits.
Rainbows form after a rainstorm because water droplets in the atmosphere act like small prisms. In order to see a rainbow, your back needs to be facing the sun. Light from the sun travels into water droplets in the atmosphere. The water droplets refract the sunlight, which contains all colours of light. Different colours of light bend different amounts inside a water droplet. Purple light bends more than red light. The difference in refraction angles separates light into its colours. Light experiences total internal reflection inside the raindrop, and then refracts again as it exits the droplet, which bends and separates the colours even more. The separated light colours travel back to your eye, which you see as a rainbow.
When white light enters and leaves a substance at an angle, it splits into its different colours. For example, when white light enters a glass prism at an angle, the light splits into its component colours when it exits.
Rainbows form after a rainstorm because water droplets in the atmosphere act like small prisms. In order to see a rainbow, your back needs to be facing the sun. Light from the sun travels into water droplets in the atmosphere. The water droplets refract the sunlight, which contains all colours of light. Different colours of light bend different amounts inside a water droplet. Purple light bends more than red light. The difference in refraction angles separates light into its colours. Light experiences total internal reflection inside the raindrop, and then refracts again as it exits the droplet, which bends and separates the colours even more. The separated light colours travel back to your eye, which you see as a rainbow.
Figure C.2.6.17– Different colours of light refract at different angles inside a water droplet.
Figure C.2.6.18– White light splits into its colours in a prism.
Watch More
The Rainbow Connection
This video explains why prisms separate white light into a rainbow.
This video explains why prisms separate white light into a rainbow.
Watch these two videos to learn more about how refracted light in water droplets creates rainbows.
Moonlight can form a moonbow in water droplets. Watch this video to learn more.
Try It!
Make a Rainbow
Try this simple experiment to create a rainbow by refracting and reflecting light.
Materials:
Try this simple experiment to create a rainbow by refracting and reflecting light.
Materials:
- Shallow pan
- Water
- Flashlight
- Mirror
- White paper
Instructions:
- Fill the shallow pan halfway full with water.
- Place a mirror at one end of the pan. The mirror should face upwards, and be tilted at an angle.
- Turn on the flashlight and aim it at the underwater mirror, at a 45° angle.
- Hold a white piece of paper horizontally above the mirror. Tilt it back and forth if necessary, until a rainbow appears on the paper.
- Watch this video to see a similar experiment and its results:
Questions:
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
Light rays from the flashlight refracted when they entered the water. Light from the flashlight was white light made up of all colours. In the water, some colours of light slowed down and bent more than others. The light, split into its colours,
reflected off the mirror and onto the piece of paper as a rainbow.
The mirror needed to be tilted so that the refracted light rays could be reflected upward onto the piece of paper.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.
Unit C Lesson 6 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Be a Self-Check
Superhero!
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
As light from the underwater section of the pipe exits the water towards the eye, it bends. This refraction of light makes the pipe under the water appear bent.
Light from the sky bends as it enters the hotter, less dense air directly above the road. This refraction of light forms an image of the sky that travels to your eye.
As light moves from air into the denser glass, it slows down and bends into a smaller angle. As light exits the other side of the glass into the less dense air, it speeds up and bends at a wider angle. The angle the light leaves the glass is
the same angle that the light entered the glass.
When the source light has a small angle, such as when you view an object from above, the refracted light also has a small angle. The similarity in angles make it possible to judge the position of an object more accurately.
When the source light has a large angle, such as when you view an object from the side, the refracted light has a much larger angle. It is harder to detect the accurate position of an object when light bends at a larger angle.
When the source light has a large angle, such as when you view an object from the side, the refracted light has a much larger angle. It is harder to detect the accurate position of an object when light bends at a larger angle.
Your back has to be to the sun and your eyes have to be facing the water spray in order to see a rainbow. Rainbows form when light from the sun refracts and internally reflects in the water droplets.