Light Energy

What is Light?

Make a list of things that give us light. How many can you think of?

Light:• Light is a form of energy that you can see.• Light is one kind of radiant energy.• Light comes from many different sources.• Some items produce light while others reflect light.

Candle producer reflector

Mirror producer reflector

Sun producer reflector

Flashlight producer reflector

Jupiter producer reflector

•Is it a producer or a reflector?

Is it a producer or a reflector?

• Name four other objects that produce light.Fire, stars, lantern, light bulb, lamp, laser, etc.

• Name four other objects that reflect light.Moon, Earth, metal, glass, water, etc

Think About It:• Where do you sit when you watch television?

discuss the question with a partner You sit in front of the television to watch it.

Demonstration: Laser Pointer• Turn off the classroom lights.• Carefully point a laser pointer at a wall• Clap chalk erasers together (or shake a nylon bag of flour)• Students describe the shape of the laser beam• It is a straight line.

How Does Light Travel?• Light travels in a straight line.

Can you think of some real-life examples of light traveling in a straight line?Sometimes discussing a lamp or light bulb can confuse students. They think light is traveling in all directions. This is not true. Light still travels in a straight line. Since the light bulb is curved, many beams of light are able to travel from its surface. However, each individual light beam still travels in a straight line from the bulb

Light Experiments• We’ve brainstormed and discussed many different sources of light.• Are all sources the same?• How might they be different? (Discuss student answers. Ex:

color, brightness, size, etc.)• Today we are going to experiment with different light sources to

compare and contrast their properties.

Light Experiments• The lights should vary in color, intensity, size/shape, and heat

produced.• Examples:• Regular Flashlight Mini Flashlight Large Flashlight• Incandescent Light Bulb Fluorescent Light Bulb• Colored Light Bulb(s) - red, blue, black, etc.• Light Bulb of Smaller Sizes - ceiling fan or reading lamp Laser Pen• Sun (visible through a classroom window)

Light Experiments• Each light source will be observed for five characteristics:1. Color of the Light2. Intensity (Brightness)3. Heat Produced4. How the Light Travels5. Real Life Uses

• Color of the Light• Turn on the light.• What color is it?• Record this information in their “Light Energy” book.

• Intensity (Brightness)• Turn on the light.• How bright is it?• Can you look at it directly without hurting your eyes? (Use caution!)• Rank the intensity on a scale of 1-5 with 1 being very weak and 5 being too bright to look at.• Record this information in their “Light Energy” book.

• Heat Produced• Turn on the light.• Place your hand in front of the beam.• How much heat do you feel? How long can you leave your hand there? (Use caution!)• Rank the heat on a scale of 1-5 with 1 being very weak or cool and 5 being very hot.

• How the Light Travels• Turn on the light.• We know light travels in a straight line.• How do the individual light beams travel from this light source? Are they all forced in one direction, or are

they able to travel in many directions?• Illustrate how the light travels from its source in their “Light Energy” book.

• Real Life Uses• What would you use this light for in real life?• Think about its properties. What uses does it have? When have you used a similar light? Why?• Examples:• Light an entire room. Look down a tiny hole.• Find shoes in a dark closet. Highlight a word on a screen. Point to a star during a show. Light the Earth.• Find a missing ball at night. Tell stories in the dark.• Holiday Decoration• Carry with you in a backpack.• Signal to a friend across the street. Etc.• Record at least one use per light source in their “Light Energy” book.

Reflection• Have the students select a partner and do a “Reflection Dance.”• The students stand facing one another. Identify one student to be “A” and

one student to be “B.”• The “A” student begins to move. The “B” student mirrors or reflects that

movement. They can move their hands, arms, legs, heads, bodies, etc.• After a few minutes, switch roles and have the “B” student lead while the “A”

student mirrors or reflects.• Finally, allow either student to be the leader or follower. They should switch

roles back and forth as they move. This is a great way for students to learn to compromise without speaking as they try to determine who is leading and who is following.

Reflection• Light can be reflected or absorbed by a surface.• When light is reflected, it bounces off that surface.• Example: Mirror• When light is absorbed, it is trapped by that surface.• Example: Your body• Light is reflected off a surface in a special way.

• Divide students into groups of two and give each pair a tennis ball.• Take the tennis ball and go out in the hall. (Remember to be respectful of other classes. J)• Both partners should kneel on the ground near an open section of wall.• Partner #1 rolls the tennis ball toward the wall.• Partner #2 tries to guess where he needs to positions his body to catch the balls at it bounces off the

wall.• Catch the ball.• Now partner #2 rolls the tennis ball toward the wall.• Partner #1 tries to guess where she needs to be to catch the ball.• Alternate taking turns rolling and catching the ball.• Be sure to vary your location when you roll the ball. Sometimes be very close to the wall and other

times be very far away.• After sufficient time to experiment, return to class.

• Discuss what was observed during the tennis ball experiment.• If I was close to the wall, where did my partner need to be? (close to

the wall)• If I was far away from the wall, where did my partner need to be? (far

away from the wall)• Help students see that the position of the student rolling the ball and

the one catching the ball where the same regardless of where they moved.

• Illustrate these observations in their “Light Energy” book.

• Let’s apply what we learned from the tennis balls to bounce passing a basketball.• Have two students stand apart facing one another in a safe area of the classroom.• Have one student bounce pass the basketball to the other.• Have the rest of the class carefully watch the imaginary line made by the basketball as it travels to

the ground, where it hits the floor, and the imaginary line made as it bounces back up.• Have the two students bouncing the basketball move closer to and father away from one another

and repeat the process.•

What happens if you bounce the basketball directly down? (It goes straight up.)• Illustrate these observations in their “Light Energy” book.• (Note: If you are able to schedule time in the gym and obtain enough basketballs, this is a great

activity to do as a whole class. This is also a great time to integrate with your PE specialist!)

Light Reflection:• The tennis ball and the basketball actually represent what happens to light as it

is reflected.• When light hits a reflective surface, like a mirror, it will bounce back at the

same angle.• The angle at which light strikes a surface is the angle of incidence.• The angle at which light reflects off a surface is the angle of reflection.• The angle of incidence is equal to the angle of reflection.• Example: When light strikes a mirror at a 45o angle, it is reflected at a 45o angle.

Draw and label an illustration of this property of light.

Reflection Activities• Group Reflection Challenge: Can you move light? Can you use what you

know about the angle of incidence and the angle of reflection to move light? Let’s find out!

• Set Up: Stand the textbook up on the desk. Lay the flashlight on a desk facing one cover of the textbook. Turn on the flashlight, so you can see the light on the cover.

• The Challenge: Move the light from one side of the textbook to the other, but you may not move the flashlight or the textbook. You may only use the mirrors and what you know about light.

Class Reflection Challenge: Have we really mastered how light moves? Let’s find out!

• Give each student a mirror. The teacher will carefully point a laser pointer into one mirror. Let’s see if we can get the light to reflect in every other mirror in the classroom. You can see a red dot on the mirror when it is successfully reflecting the laser.

• What worked well? What didn’t? Why? ______________________• ____________________________________________________________

______________________________________________• • What would you do differently next time? _____________________• _____________________________________________________• What is our record for the most number of mirrors reflected?

• Helpful Hints:• Remember what we’ve learned about the angle of incidence and angle of

reflection.• Setting the laser pointer on a table will help hold it steady.• Having students place their mirrors on desks and tables will also keep

them steady.• Be sure to let students suggest ideas and methods.Allow them to explore

and problem solve. This is a challenge, not a demonstration.• Keep a running count of how many mirrors you have successful reached.

Can you beat your own record?

Mirrors that Multiply:• Use a hinged mirror. • Test angle AOJ. How many faces do you see in the mirror?

• Test angle BOI. How many faces do you see in the mirror?

• Test angle COH. How many faces do you see in the mirror?

• Test angle DOG. How many faces do you see in the mirror?

• Test angle EOF. How many faces do you see in the mirror?

• What pattern do you see?• The larger the angle, the fewer faces.• The smaller the angle, the more faces.• Why? (As the angle gets smaller, the light is able to reflect back and

forth in the mirror more frequently resulting in more images.)

Butterfly Designs• Use one mirror to reflect portions of the butterflies to create full

pictures or new designs.

Reflected, Absorbed, or Transmitted?• Introduction:• Light can be reflected - bounced off an object.• Can you think of an example? (mirror)• Light can be absorbed - trapped by an object.• Can you think of an example? (desk)• Light can also be transmitted by - or pass through an object.• Can you think of an example? (window)

Reflected, Absorbed, or Transmitted?

• Light that passes through matter is transmitted by the material.• If light is not transmitted, some if it is reflected.• If light is not transmitted or reflected, it is absorbed.• There are three types of materials:• Transparent: light is transmitted (passes through)• Translucent: some light is transmitted, some is reflected and scattered• Opaque: light is absorbed (not transmitted or reflected)

Transparent, Translucent, or Opaque?• Use a flashlight to test each item. List it in the correct category.

Transparent Translucent Opaque

Refraction• Activity: Cup of Water•

• Put your thumb in the glass of water. What do you observe?•

• Put a drinking straw or pen/pencil in the glass of water. What do you observe?

• Refraction:• When an object is placed in a glass of water it appears to be

broken or shifted to the side. This is because of light refraction.

• Light changes direction when it enters a new medium.• A medium is any substance through which a wave is

transmitted.• Example: Light is traveling from the overhead light bulbs

through air. When the light enters the cup of water, it enters a new medium. This causes the light to change direction.

• Light in air travels fast.• Light in water travels more slowly.• When light slows down, it changes direction.• When light changes direction or bends, it is called refraction.• Refraction is caused by the change of the speed of light as it travels

through different mediums.

• Close your eyes and imagine running across a dirt field. With your arms and legs “run” as quickly as you can.

• Imagine a large puddle in the field. You run into the puddle.• The water is up to your ankles, then your knees, then your thighs. Show with your

arms and legs that you are running more slowly.• The water is up to your waist then your torso and shoulders. “run” slower and slower.• You’ve now reached the middle of the puddle, and you begin to run out the other

side. The water level drops to your torso, waist, legs, knees, ankles, and feet. Adjust the speed of your “running” faster and faster as you get free of the water.

• Once you are free of the water and once again running across the field, open your eyes.

• That just like we slow down as we try to run in water, light also slows down when it enters water.

• This change of speed, changes the direction of the light and is called refraction.

• Activity: Throwing Contest• Who has a great throwing arm?• Volunteer throws a ball at a safe wall of the classroom while you shine a laser

pointer on the wall at the same time.• Identify a starting line.• 1, 2, 3, Go! Have the student throw the ball while you turn on the laser pointer.

Have the rest of the class watch the wall. Who won? (laser)Repeat the contest a few times allowing several students to try. The laser pointer will win every time.

• Have the students record the results of the contest in their “Light Energy” book and discuss why they think that happened?

• Speed of Light:• The speed of light is 186,000 miles per second.• That is the same as 7 ½ times around the Earth in 1 second. (Imagining

light can bend, since we know it really travels in a straight line.)• (The laser will always win. You can never through a ball that fast.)• This is how fast light travels in air. When it enters a new medium (like

water), it slows down. The results is refraction.

• Appearing Coin:

• Look at the cup from the side so you can still see the bottom of the inside of the cup, but you cannot see the coin glued to the bottom.

• Slowly pour water into the cup until you see the coin appear.• Why does it work? The coin didn’t move. The cup didn’t move. The water caused the light to bend and made the coin visible. It’s refraction!

• Have you ever played a diving game while swimming. You drop a coin or some other toy to the bottom of the pool and have a contest to see who can dive down and retrieve the object first? Ask students if they have ever been frustrated during this activity. From the surface, you are sure you know where the object is, but once you dive under the water it seems to move. Why? Refraction, of course!

Refraction Experiments• Variable: Amount of Water• First, let’s experiment by changing the amount of water and see how

it affects refraction.• Have students measure 50 mL, 100 mL, 150 mL, and 200 mL of water

into four different clear plastic cups.• Place a drinking straw in each cup being sure the angle of the straw is

the same for each container.• Record the observations in their “Light Energy” book.

Refraction Experiments50 mL of Water 100 mL of Water 150 mL of Water 200 mL of Water

Illustration: Illustration: Illustration: Illustration:

Observation:

Observation: Observation: Observation:

• Variable: Type of Liquid• Now let’s experiment by changing the type of liquid and see how it

affects refraction.• Have the students measure 100 mL of water, vegetable oil, karo syrup,

and rubbing alcohol into four different clear plastic cups.• Place a drinking straw in each cup being sure the angle of the straw is the

same for each container.• Record the observations in their “Light Energy” book.

• Pour 100 mL of each liquid into each glass. Place a drinking straw in each cup being sure the angle of the straw is the same for each container. Record your observations.

Water Vegetable Oil Karo Syrup Rubbing Alcohol

Illustration: Illustration: Illustration: Illustration:

Observation: Observation: Observation: Observation:

Color of Light• Introduction:• Hold up a series of objects.• Have the students identify the color of each item.• How do you know what color it is?• What makes it red or blue or green? Why is it that color?

Color of Light• Light Waves:• Light travels in waves.• Have the students draw and label a light wave in their “Light Energy“

book. The top of a wave is crest. The bottom of a wave is a trough. The distance from the base line to the crest or trough is amplitude. The distance from one crest (or trough) to another is one wavelength.

• Frequency is the measure of the number of waves that pass by a given point in one second.

• Remember, light is one kind of radiant energy.• Radiant energy includes waves of all different wavelengths and

frequencies.• When all the types of radiant energy are arranged in order, we have the

Electromagnetic Spectrum.• Have students study the diagram of the Electromagnetic Spectrum in their

“Light Energy” book. – will show you more examples so wait• Notice that the wavelengths range from long to short, and the frequencies

range from low to high.• Briefly discuss each component of the Electromagnetic Spectrum.

Summary• Summarize what we have learned so far about light:• Light can be reflected (bounced off).• Light can be absorbed (trapped).• Light can be refracted (bent).• Light can be separated (creates rainbow).

The Electromagnetic Spectrum:• Visible Light:• We can only see one portion of the electromagnetic spectrum. That portion is called

visible light.• What color is the light from most light bulbs? (white)• Although we see white light, it is actually made up of many colors.• The colors of the spectrum are: red, orange, yellow, green, blue, violet.• An easy way to remember these colors in order is: ROY G. BiV• Notice that the i in BiV is lower case. That is because indigo is not part of the spectrum.

Indigo is a real color, but it is not part of the six-color spectrum. Legend says that when Isaac Newton discovered the visible light spectrum, it really bothered him that there were only six colors. Seven was his lucky number, so he added in indigo to have seven colors.

Class Activity: Prism• White light appears while to our eyes, but it is actually made up of the

colors of the visible light spectrum. Test several different types of light bulbs and discuss what students observe. Have them use their observations to make predictions for the next bulb before it is plugged in.

• Class Activity: Prisms• The lenses of the glasses we used to see the true colors of visible light are similar to prisms.• Prisms separate light into the colors of the spectrum.• Give students a prism and flashlight and let them experiment with try to create a rainbow.• (Note: The more prisms you have for students to use, the more successful this activity will

be. However, prisms are expensive. If you are only able to obtain one prism, do this activity as a demonstration instead.)

•Have students record which technique worked best to create a rainbow using a prism in their “Light Energy” book. (Shining the flashlight on the edge of the prism works best.)

• Once students have experimented with prisms and flashlights, take them outside to see how the sun affects prisms.

• Have them use what they learned using a flashlight inside to make a rainbow using sunlight.• (Note: Have students stand on the grass for this activity. Prisms accidentally dropped on

the grass survive much better than those dropped on cement. J)

• Prisms separate light into the colors of the spectrum. Use a prism and a flashlight to see if you can create a rainbow. What technique works best? ______________________________

• Is a prism the only way we see a rainbow? (no)• When do you usually see a natural rainbow? (after rain)• How was that rainbow created? What caused the sunlight to

separate? (The water vapor left in the air after a rain storm acts as a prism to separate the light.)

• 60 watt light bulb:• All six colors of the spectrum stretch from the light bulb.• The colors of the portions are even in size.• 100 watt light bulb:• All six colors appear.• The lengths are much bigger and brighter due to higher wattage.

• Red light bulb:• The red portion is much stronger and longer than before.• It is so strong that the other colors are much smaller and some have

even disappeared.• Why? Red is the strongest color in the spectrum.• If you were to close your eyes and look at page of colors, your eye

would see red first.• That is why Coke cans are red.

• Blue light bulb:• The blue is the strongest and biggest color. The other colors are still

present, just smaller.• Why? Blue is the second color you see after red. That is why Pepsi can

are blue.

• Green light bulb:• Green is the strongest and biggest.• The others colors are still present, just smaller.

• Halloween Black Light:• Only a small amount of light is seen and most of it is purple

• True Black Light:• Nothing will be seen.• Why? White reflects all light. Black absorbs all light. There is nothing

reflected to be seen.

Activity: Blending Light• We can use a prism to separate the colors of white light, so we can

see all the colors of the spectrum. Is it possible to blend the colors of light and make white? Let’s find out. Record your observations.

• Activity: Blending Light• We can use a prism to separate the colors of white light, so we can see all the colors of the spectrum. Is it possible to

blend the colors of light and make white? Let’s find out.• The primary colors of pigment (paint) are red, yellow, and blue.• We can mix these colors to make secondary or tertiary colors.• If you mix all the primary colors, you get “yuck.”• (Note: This is a great time to integrate the art concept of hue.)• The primary colors of light are red, green, and blue.• What happens if we mix them?• Cover the ends of three flashlights with pieces of red, green, and blue cellophane secured with a rubber band.• Have three students turn on and point the three flashlights at a white overhead screen or white board.• Identify each separate color.• Then invite the students to cross their beams and mix the colors in one location on the board.• In the very center, where all three colors combine, you get white.• Repeat the process by separating and mixing the colors a few times.• (Note: The activity is more successful if the three flashlights are all the same brand and have new batteries. The tint

of your cellophane may not be perfect, but students should still see that the color in the center of the mix is much, much lighter than when the colors are separated.)

• Record student observations in their “Light Energy” book.

Colors:If light is made of all the colors of the spectrum, how do we see certain colors? Why do we see white, black, or red?White:• All the colors of the spectrum strike the surface.• All the colors of the spectrum are reflected to our eyes.

Black:

• All the colors of the spectrum strike the surface.• All the colors of the spectrum are absorbed. (None are reflected.)

Red:• All the colors of the spectrum strike the surface. Red is reflected to our eyes.• The rest of the colors are absorbed.

• Yellow:• All the colors of the spectrum strike the surface. Yellow is reflected to

our eyes.• The rest of the colors are absorbed.• Green:• All the colors of the spectrum strike the surface. Green is reflected to

our eyes.• The rest of the colors are absorbed.

Color of Light ExperimentsTest each object according to the chart. Record the color observed.

Object Color:

Red Filter Orange Filter Yellow Filter Green Filter

Blue Filter Violet Filter

Red

Orange

Yellow

Green

Blue

Violet

White

Layer the colored filters and see what effects are created. Record your results• Filter colors used: Result:• __________________ __________________• __________________ __________________• __________________ __________________• __________________ __________________• __________________ __________________• __________________ __________________