Introduction to Light
Part of:
Inquiry Science with Dartmouth (a new program!)
Developed by: Mike Mastanduno
Adapted from: Kahn Academy
Overview
Students will use a slinky and a microwave to explore the properties of waves (frequency and
wavelength) and have a general understanding of electromagnetic radiation.
Science Standards (VT Science Curriculum Frameworks)
Space, Time, Matter – Matter, Motion, Forces, Energy:
7.12ee: Identify and describe commons forms of energy (e.g., light, heat, sound, electricity,
electromagnetic waves) and their attributes, sources, and transmission characteristics (e.g.,
radiation, convection, conduction of heat)
Space, Time, Matter – Design and Technology:
7.17aa: Apply the basic processes involved within each technological system (e.g., construction,
power and transportation, communication, and manufacturing)
7.19aa: Create a design solution: Build on specifications, with an understanding of the
constraints (e.g., cost, weight, environment), and tolerances that affect performance; Include
mathematical and/or mechanical models of their design; Include steps and sequences for
efficiently building a prototype that conforms to the specifications; Test the prototype; Use the
results to modify the design.
Focus Question
Why is light important?
Objectives
Through this lesson, students will:
o Define electromagnetic radiation
o Demonstrate the concepts of frequency and wavelength using a slinky
o Discuss similarities and differences between slinky waves and EM radiation
o Draw a picture of how a microwave creates heat (energy) using waves
Background
At this point, the students should have learned about energy and heat transfer. Review basic
types of energy (kinetic, potiential, thermal) and types of heat transfer (conductive, convective,
radiative).
Vocabulary
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Energy
Electromagnetic Radiation
Particle
Photon
Wave
Frequency
Wavelength
Medium
Materials (For 1 class of 10-20)
• 1 Slinky, 10-15 feet in length (you might want to connect 2 Slinkies together)
• 1 bag mini marshmallows
• Glass baking pan
• Microwave
Preparation
Line the baking pan with a layer of mini marshmallows and set it aside. Prepare the microwave
by removing the spinning plate in it so that the pan will not move. Also record the operating
frequency of the microwave, listed on the back. Should be around 2.45GHz. Pull up The Kahn
Academy’s video, “Introduction to Light” on a projector.
Procedure
Note: the microwave portion of this class can be left out or saved for day 2.
1. Introduction: You are a scientist, you work with light in medicine. Convey that it’s awesome.
2. Hook: Light is all around us! It’s the fastest thing we know and many technologies depend
on light.
3. Background: This is a basic introduction. They need to know underlying concepts of energy
and heat transfer, but nothing else.
4. Video (10 minutes): You and the students will watch the Kahn Academy video, “Introduction
to Light.” They will take write down concepts they are unfamiliar with. Emphasize that they
should only write down one word on a concept so they can still pay attention to the video.
While watching the video, write main ideas on the board: wave, particle, photon, frequency,
wavelength, medium.
5. Discussion of vocabulary (10 minutes): Discuss each term written on the board and others
that the students come up with. Look for the parallels to their lives!
6. Demonstration (20 minutes): Ask for volunteers to operate the slinky (2 at a time). Illustrate
pulses of single waves, transverse waves, reflection, when 2 waves collide, standing waves
with 1, 2, 3 nodes. Relate to vocab that you already covered but don’t worry about more
advanced terms. Observations of the behavior are the most important part.
7. Extension (20 minutes): Describe how a microwave works in reference to the sanding wave
on the slinky. Then microwave the pan of marshmallows until there are burned spots in the
pan (2 min or so). Measure the distance between burned spots (half wavelength) and use the
relationship c = lambda*frequency to calculate the speed of light.
8. Consolidation: Relate activity back to the background and your research.
a. Why do microwaves have spinning plates in them?
b. Why did our eyes develop to be able to see visible light and not xrays or
microwaves?
c. What other technologies could we use light for?
9. Additional thought experiment: What do wavelength and frequency have to do with colors?
10. Wrap-up: We moved into how light interacts with matter next. A thought experiment
concerning the nature of color in clothes was a good close. IE, is a red shirt still red under
only green light?
Assessment
• During the activity: Ask questions that require synthesis of knowledge to demonstrate
understanding. Example: Are waves at the beach waves? How do they have a frequency?
How do you measure it?
• After the activity: Use the attached light quiz or individual questions from it. We gave this the
following week.
Extensions
Students could be encouraged to:
• Build a solar oven that traps sunlight to make grilled cheese.
Name_____________________________________
Light Quiz
1. Electromagnetic radiation is a type of energy that travels through space like a wave. Give 4
examples.
2. Light can be thought of as both a wave and a particle.
a. Define wave:
b. Give 2 examples of waves.
c. Define a particle:
d. Give 2 examples of particles.
3.
a. What is a medium?
b. Do all waves require a medium to travel?
c. Give 2 examples of waves that require a medium.
d. Give 2 examples of waves that don’t require a medium.
4. What is frequency (think about clapping if you’re stuck)?
a. How would you measure the frequency of the waves at the ocean?
5.
a. What is a wavelength?
b. Do all waves have a wavelength?
c. How would you measure the wavelength of this wave?
6. Is there a relationship between wavelength and frequency? Think about how we made the
waves on the slinky if you’re stuck.
7. A microwave works by using a standing wave to vibrate the molecules in your food and
warm it up. The wave moves back and forth between the long dashed line and the short
dashed line.
a. Label the parts where you think food would warm up the fastest and where it would
warm up the slowest.
b. Why did you choose these spots?
c. Finally, why do microwaves have spinning plates in them?