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Electromagnetic Spectrum

Author: Mark Roland
Edited by Stephanie Nardei and Rachel Hughes


Time: 2 class periods
Preparation Time: 10 Minutes
Materials:

Internet access

 

Abstract
The various types of wavelengths along the electromagnetic spectrum are encountered every day. Differences and similarities between the types of waves are often misunderstood. During this lesson, students will learn about the following:

  • electromagnetic spectrum
  • the concept of photons
  • the energy levels of electromagnetic waves

The topic will be introduced as an environmental health theme of potential dangers and how to minimize them.

Objectives
Students will be able to:
1. Define electromagnetic radiation.
2. List major categories of electromagnetic waves and uses.
3. List potential health risks with electromagnetic waves.
4. Demonstrate understanding of Plank’s constant by solving quantitative equations on wavelength, frequency, and energy.

National Science Education Standard
Content Standard B-Physical Science
INTERACTIONS OF ENERGY AND MATTER

  • Waves, including sound and seismic waves, waves on water, and light waves, have energy and can transfer energy when they interact with matter.
  • Electromagnetic waves result when a charged object is accelerated or decelerated. Electromagnetic waves include radio waves (the longest wavelength), microwaves, infrared radiation (radiant heat), visible light, ultraviolet radiation, x-rays, and gamma rays. The energy of electromagnetic waves is carried in packets whose magnitude is inversely proportional to the wavelength.

Content Standard F- Science in Personal and Social Perspectives
SCIENCE AND TECHNOLOGY IN LOCAL, NATIONAL, AND GLOBAL CHALLENGES

  • Science and technology are essential social enterprises, but alone they can only indicate what can happen, not what should happen. The latter involves human decisions about the use of knowledge.
  • Understanding basic concepts and principles of science and technology should precede active debate about the economics, policies, politics, and ethics of various science- and technology-related challenges. However, understanding science alone will not resolve local, national, or global challenges.

Teacher Background
http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html (description of electromagnetic spectrum)
http://lectureonline.cl.msu.edu/~mmp/applist/Spectrum/s.htm (spectrum applet)
http://radiojove.gsfc.nasa.gov/class/lesson_plans/lesson4.pdf (practice problems)
http://www.colorado.edu/physics/2000/applets/h2o.html (microwave applet).

Related and Resource Websites
None

 


Activity
Day 1
1. Write this question on an overhead or on the board:
“Can microwaving your food give you cancer?”

2. Let students react to question and discuss as a class what they know about the topic. Is it true? If microwaving doesn’t cause cancer, is it bad for you in other ways?

3. After students have expressed opinions and thoughts, remind them that “basic concepts and principles of science and technology should precede active debate about the economics, policies, politics, and ethics of various science- and technology-related challenges. “ (NSES 1994) What do they know about the science behind microwave ovens?

4. Review ideas on previous lesson titled “The Wonderful World of Waves.” This is an opportunity to address some concepts students didn’t explore in the previous lesson. Ask students what happened to the far end of a medium (i.e., the jump rope, telephone cord, etc.) as a generated wave reached it. They should say it moved, and if there was movement, then there was a force, so there was energy. The idea is a wave transmits energy.

5. If any groups studied speed of waves in the previous lessons, they may have noticed some mediums transmitted waves more quickly than others. The “lighter” the medium was, the wave should have traveled faster. For example, a wave will travel faster through a piece of string than through a heavy jump rope.

Electromagnetic waves can travel through a vacuum, which is at the extreme far end of a “lightness” spectrum, having no mass. Therefore, they go very fast--at the speed of light. This is not an exact scientific explanation, but it will make the point.

6. Ask students the following question:
A wave has a wavelength of three feet and a frequency of two hertz. How fast is the wave traveling?

Hints—Think about the algebraic formula for speed and try drawing a diagram of the two wavelengths.

Give students sometime for this question and monitor the class to steer them if necessary. If they draw an appropriate diagram, they should see the connection. If two full wave cycles are propagated each second (that’s what two Hertz describes) and each one is three feet long, then the wave must be traveling at 6 ft/s.
Speed = where is the frequency, and is the wavelength

7. Students make the connection to electromagnetic waves. All electromagnetic waves travel at the speed of light. Thus, the following must be true:
c =
where c is the speed of light, is the frequency, and is the wavelength

8. Have students go to the website listed above titled spectrum applet. This applet allows them to see there is a relationship between frequency and energy. If they are related, there must be some mathematical formula including them. Introduce Plank’s constant and the following equation:
E=h where E is energy, h is Plank’s constant, and is the frequency

9. As a class practice problems using these two formulas. There are some on the website titled practice problems, about two or three pages down (it is a large Adobe (PDF) file). The rest of the day could be used for working on these problems for homework.

Day 2
1. Review formulas students were introduced to in yesterday’s class by going over homework problems. Answer questions students might have.

2. Have students return to website titled spectrum applet. Use this as a resource and begin a table in their notes including each major type of radiation, what its sources are, how it’s measured, and leave a column for possible environmental health risks. List the wave types from low to high energy.

3. Once students have completed the table (except for the environmental health column), have them look at the website titled microwave applet. This is a good demonstration of how a microwave passing through a water molecule causing the molecule to vibrate. Remind them of the polarity of a water molecule.

4. Assign two or three students (depending on the class size) to each type of electromagnetic wave. Ask them to research the potential environmental health risks associated with them and to be prepared to present their findings to the class. They should find at least two sources in order to confirm any information discovered.

5. Have each group present what they found and ask them to fill in the rest of their note chart as information is presented.


Closure
Ask class what patterns they notice with environmental health risks. If they conducted good research, they should notice the higher the energy level of radiation, the greater potential risk. Ask them to note where microwaves are on the spectrum. What common waves are closest? Ask students again whether they think microwaves can have environmental health risks. What exposure to microwaves do microwave ovens and micro-waved food provide to users, if any?

Homework
Practice problems using and E=h and c = for homework on the first night.

Embedded Assessment
Students ability to achieve standards can be assessed based on class discussions and first night’s homework.

 

 

 

 

 

 

 

 

 

 


PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:


an
NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award

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Supported by NIEHS grant # ES06694


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Last update: November 10, 2009
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