By Ginger Butcher, NASA Goddard and Deborah Roberts-Harris, University of New Mexico This lesson is a demonstration about the scattering of light waves. Students will investigate how scattering occurs when light reflects off an object in different directions. Students will experience an analogue for how light waves are affected as they travel through the atmosphere. Concepts of wavelength and scattering are introduced. STUDENT OBJECTIVES Students will compare and analyze data by measuring energy from light waves as they are scattered. Students will explore how light waves reflects off an object in a variety of directions. Students will be able to explain how this investigation is similar to how particles in the atmosphere can scatter light waves. Students will understand how scientists use satellite instruments can measure scattering of light to detect different gases and particles in the atmosphere. KEY TERMS Electromagnetic spectrum, spectrum of visible light, scattering, wavelength, sensors APPROXIMATE TIME 30-45 minutes MATERIALS – littleBits™ components: power, bright led, and energy meter (power + light sensor + wire + number bit) – Erlenmeyer flask or large glass bottle with a shoulder large glass jar or beaker – Water – Opaque liquid such as cream or coffee creamer milk – 2 books to set the the jar/beaker on – Photos/images as noted SETUP: Fill glass container with water up to about an inch from the top 1. Put together first circuit: power, bright led 2. Set glass container on two books leaving a gap large enough for the light sensor 3. Assemble the sensor circuit: power + light sensor + wire + number bit Teacher Note: Dim/turn off classroom lights and close blinds on windows close to student desks for this activity, so that the light sensor is only sensing the light through the jars. Florescent light is easily detected by the light sensor and skews the readings. Also Erlenmeyer flasks work well for this activity because measuring from the neck of the flask is like the light reflecting back to the satellite. NGSS – DISCIPLINARY CORE IDEAS MS-PS4-2 Waves and Their Applications in Technologies for Information Transfer – Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials. [Clarification Statement: Emphasis is on both light and mechanical waves. Examples of models could include drawings, simulations, and written descriptions.] [Assessment Boundary: Assessment is limited to qualitative applications pertaining to light and mechanical waves.] NGSS – Cross-cutting concept Patterns: Graphs and charts can be used to identify patterns in data. To see a recording of this session: http://youtu.be/QgVINPnH0OQ
Duration: 45 min
Middle School (ages 11-13)
Earth & Space Science
MODULES & ACCESSORIES USED (5)
light sensor (1)
bright led (1)
STEP 1 : Engage: Colors in the sky
Asks students “What colors do you see in the sky?” Ask students to get with a partner to think-pair-share about colors they see in the sky and what is causing the different colors. Record responses from the think-pair-share.
Use these questions to help guide students to think about what is in the atmosphere (such as particles, air, oxygen we breathe, pollution).
•What happens to light as it travels from the Sun to Earth where we can see it?
•What do you think light passes through on the way here?
•Is there anything different between what is in space and what is in our air (atmosphere)?
Now we are going to investigate how light can be affected when it travels through the atmosphere.
STEP 2 : Explore: Taking measurements
Ask students to take the readings and record data on their data sheet.
1. One student holds the light on top of the container shinning down.
2. Another student holds light sensor to the side of the container, near the top, and reads the number bit reading. Record data.
3. Then take a reading with the light sensor at the bottom of the container by placing sensor between the books – making sure the number bit is still readable. Record data.
4. Add a 5 drops of creamer to the water. Take both measurements again and record data. Repeat trial 3 more times, each time adding 5 more drops of creamer.
STEP 3 : Explain: What is happening to the light?
Ask students to graph the data from their data table and answer the following questions:
1. What did you observe in the change in the measurements as you added milk?
2. What did you observe in the change between the two measurements as you added milk?
3. Was your hypothesis correct?
4. Do you see a pattern in the data?
5. What is happening to the light in this experiment?
Invite students to share their interpretations with the class, making sure that when they share their analysis they are using data from the table to support their claims. Probe students answers that imply that light is scattering or bouncing off the milk particles.
All light travels in a straight line unless something gets in the way to:
•bend it (like a prism)
•or scatter it (like molecules of the gases in the atmosphere)
As the light travels through the water it interacts with the molecules of water and the suspended particles of milk. As more milk is added, more light is scattered back in all directions and less light reaches the bottom. In contrast, the more the light is scattered, the more light is scattered out the side of the glass.
STEP 4 : Extend: How satellites measure the atmosphere
Discuss with your partner how this diagram relates to our experiment. You can add your own labels to the diagram to show how the experiment is related. Have students share ideas and answers.
STEP 5 : Explain: Satellites and Remote Sensing
In this experiment, the bright LED represents the sun. Measuring the light from the bottom of the glass represents measuring the light from the ground – at the bottom of the atmosphere. When sunlight reaches the atmosphere of the Earth, there are many gases and particles in the air, just like there were particles of milk in your glass.
The light waves, are scattered by these substances, just as the light was scattered by the particles of milk. Measuring light from the side of the glass represents taking measurements from space, like onboard a satellite. The satellite sensor “sees” the light being scattered.
STEP 6 : Extend: Why is the sky blue?
Refer back to the list of sky colors from the beginning of this lesson. Ask students “What did we learn in this experiment that might help us explain the colors in the sky?”
Play movie from 01:17 – 2:00
STEP 7 : Evaluate
Have students provide explanations for the what causes different colors in the sky.
1. Black – no Sun, no light, dark
2. Blue – blue light waves are scattered by molecules in the atmosphere (Rayleigh scattering)
3. White – all light waves are scattered (overcast or pollution) or reflected (clouds)
4. Red and orange – as the Sun is lower in the sky is passes through more atmosphere. More and more of the short wavelengths (blues and greens) are scattered and only the red and orange wavelengths get through.