Teacher Guide

The Secret World of Light

GEMS

November 4, 2017

Florida Science Standards Covered

SC.7.P.10.1—Grade 7Illustrate that the sun's energy arrives as radiation with a wide range of wavelengths, including infrared, visible, and ultraviolet, and that white light is made up of a spectrum of many different colors.

SC.8.E.5.11Identify and compare characteristics of the electromagnetic spectrum such as wavelength, frequency, use, and hazards and recognize its application to an understanding of planetary images and satellite photographs.

SC.912.P.10.18—Grades 9-12Explore the theory of electromagnetism by comparing and contrasting the different parts of the electromagnetic spectrum in terms of wavelength, frequency, and energy, and relate them to phenomena and applications.

Materials Needed

Internet access to show videos

Activity 1: Remote control units (e.g., TV) and smartphones

Activity 2: black construction paper, highlighter pens (pink, yellow and orange work best), UV light source (https://www.amazon.com/gp/product/B06WP4QP8G/ref=s9_acsd_hps_bw_c_x_2_w)

Activity 3: A variety of fluorescent and phosphorescent objects. For example:

Glow in the dark tattoos (phosphorescent), available at Amazon.com Glow in the dark stars (phosphorescent), available at Amazon.com Tonic water (fluorescent—blue) Glow in the dark pebbles (phosphorescent), available at Amazon.com Irish spring soap (fluorescent—green) Laundry detergent with brightening agent (fluorescent) Vaseline (fluorescent) Glow in the dark playing cards (phosphorescent), available at Amazon.com Fluorite rocks (phosphorescent), available at Amazon.com

Activity 4: Wintergreen lifesavers, source of UV light

Activity 5: White bandanas, highlighters with fluorescent ink (pink, yellow and orange work best) and phosphorescent fabric paint markers (http://www.orientaltrading.com/glow-in-the-dark-fabric-paint-pens-a2-48_2365.fltr?keyword=glow+in+the+dark+paint)

I. What is light?

Ask students to come up with a definition of light

Ask if they think all light is the same. Are there different kinds of light?

Ask what’s different between different types of light

Show video:

https://www.youtube.com/watch?v=O0PawPSdk28&t=34s

Light is tiny packets of energy. Light is the packets we can actually see. The energy that we can’t see we can think of as invisible light, or radiation. Not all light has the same energy The electromagnetic spectrum below shows the how we characterize light and other kinds of radiation by wavelength (how narrow or wide the wave is) and frequency (how many waves pass by a point in a certain amount of time). Shorter wavelengths = higher frequency and higher energy.

Visible and invisible light

Ask students how we detect visible light (from a lightbulb). Explain the difference between the source and detector.

Eyes, Cameras

Tell students that the energy wavelengths just below and just above the range of visible light can also be detected. These wavelengths can be thought of as “invisible light” or radiation.

X-rays:

X-ray: A dentist uses X-rays to image your teeth, and airport security uses them to see through your bag.

Gamma rays:

Gamma ray: Doctors use gamma-ray imaging to see inside your body. The biggest gamma-ray generator of all is the Universe.

Show video:

https://www.youtube.com/watch?v=PPlrtgilgK8

https://www.nasa.gov/press-release/nasa-missions-catch-first-light-from-a-gravitational-wave-event 

Ask students to give an example of a detector for radio waves and microwaves

Radiowaves:

Radio: Your radio captures radio waves emitted by radio stations, bringing your favorite tunes. Radio waves are also emitted by stars  in space.

Microwaves:

Microwave Oven: Microwave radiation will cook your popcorn in just a few minutes.

Activity 1: Detecting Infrared light waves

From: https://www.carolina.com/teacher-resources/Interactive/detecting-ir-light-with-a-smart-phone/tr32422.tr

Let’s look at one way you probably use infrared light all the time without even knowing. You can actually use your smart phone to detect infrared light that comes from a TV remote control.

1. Aim the remote at your neighbor. Press any one of the buttons several times. Does your friend see any light? (Don’t worry… infrared is long wavelength, low energy light. It won’t hurt your eyes.)

2. Next open the camera app on a smart phone. Switch the camera to front-facing.

3. Now aim the remote at the front-facing camera. Press any button on the remote. Do you see any light with your smartphone camera?

4. Repeat the procedure using the rear-facing camera. What happens?

Why does one camera work but not the other one? No, the rear-facing camera is not broken. It’s designed to prevent infrared light from passing through the lens; therefore, no light is seen on the screen.

To improve photo quality and to make images appear more like what we actually see with our eyes, camera makers apply films and filters to block out infrared light. This process maximizes the amount of visible light that goes through the lens.

Activity 2: Detecting UV light waves

In this activity, you will use a pen that is a UV light source. The detector will be the ink in a highlighter.

1. Write your name on a piece of black paper using the highlighter end of the pen.

2. Turn the lights off.

3. Shine the UV light source end of the pen on the highlighter writing. What happens? Did you successfully detect the UV light waves?

It glowed under the UV light.

Making the invisible visible

Your name should have glowed under the UV pen light. This is because the ink went from a low to high energy state when it absorbed the UV light waves. (Remember that short wavelengths = high energy?) As the ink went from high-energy back to the low-energy state, the energy was given off or emitted as a glow—visible light that you detected with your eyes.

This process is called LUMINESCENCE. Luminescence can be divided into fluorescence and phosphorescence. The difference between fluorescence and phosphorescence is how long the absorbed energy continues to be emitted.

Did your name keep glowing after you stopped shining the UV pen light on it? NO! This is an example of FLUORESCENCE. Can you give another example of fluorescence?

Fluorescent lights are one example. There is a powder coating on the inside of the lightbulb that absorbs the visible light and emits it as a bright, bluish-white glow.

Phosphorescent objects continue to glow even when you stop shining the UV pen light on them. That’s because it takes longer for the energy that was absorbed to leave phosphorescent materials. Depending on the material, phosphorescence can last for hours!

Some animals can make chemicals that are luminescent, mostly animals that live in the deep ocean. Scientists estimate that 80-90% of deep-dwelling animals are bioluminous. Why do you think some animals bioluminesce?

This might help them attract a mate, lure prey or confuse predators.

Show video: start at 7:17, go to 5:16

https://www.ted.com/talks/edith_widder_the_weird_and_wonderful_world_of_bioluminescence

Activity 3: Identifying fluorescent and phosphorescent objects

In this activity, you will test different objects and determine if they are fluorescent or phosphorescent.

1. Shine your UV pen light on each object and see if it glows.

2. Stop shining the UV pen light and see if it continues to glow

3. Indicate which objects are fluorescent and which are phosphorescent

Objects that glow only under the UV light are fluorescent, while those that continue to glow without the UV light are phosphorescent.

Activity 4: Another kind of light energy—Triboluminescence

Energy that comes from smashing or tearing something—called mechanical energy—can sometimes be transformed into light energy. It happens when you smash hard sugar-based candies as the crushing of the sugar molecules transmits energy to the nitrogen in the air around us. The nitrogen wants to get rid of that energy so it releases it as light. It’s mostly UV light, but some visible light, too. This is similar to what happens when you see lightning in the sky.

Let’s see if we can create triboluminescence with wintergreen Lifesavers. Wintergreen flavor works best because the wintergreen oil is fluorescent, so it captures and re-emits light like the way the highlighter ink does.

When the lights are out, with your mouth open, bite down on a lifesaver and see if your neighbor can see any triboluminescence as it’s crushed between your back teeth. Try shining the UV light from your pen at the lifesaver while your neighbor bites a lifesaver. Does that help?

Show Video: Start at 0:22, go to 2:22:

https://www.youtube.com/watch?v=tW8q_JfmcbU

Activity 5: Make a luminescent bandana

Decorate your bandana with the highlighters and fabric markers on your table. Predict what you think will happen when we turn off the lights and you shine the UV light on your decorations. Which will be fluorescent? Which will be phosphorescent?

References

https://www.wired.com/2011/01/bioluminescent-sea-creatures/

https://recipes.howstuffworks.com/question505.htm