Electromagnetic Radiation

MCAS Standard

6. Electromagnetic Radiation
Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum.

6.1 Recognize that electromagnetic waves are transverse waves and travel at the speed of light through a vacuum.

6.2 Describe the electromagnetic spectrum in terms of frequency and wavelength, and identify the locations of radio waves, microwaves, infrared radiation, visible light (red, orange, yellow, green, blue, indigo, and violet), ultraviolet rays, x-rays, and gamma rays on the spectrum

NOTES
The Physical Nature of Light--Electromagnetic Radiation
Central Concept: Oscillating electric or magnetic fields can generate electromagnetic waves over a wide spectrum.

•6.2 Describe the electromagnetic spectrum in terms of frequency and wavelength, and identify the locations of radio waves, microwaves, infrared radiation, visible light (red, orange, yellow, green, blue, indigo, and violet), ultraviolet rays, x-rays, and gamma rays on the spectrum
The Electromagnetic Spectrum
Objectives
􀀳* Learn the relationship among
the frequency, energy, and
wavelength of light.
􀀳* Learn how the speed of light
changes in different materials.
􀀳* Identify the different kinds of
electromagnetic waves.

The Electromagnetic Spectrum Vocabulary
electromagnetic wave
•electromagnetic spectrum
•Radio wave
•microwave
•infrared light
•visible light
•ultraviolet light
•X rays
•gamma rays

Light is an electromagnetic waveWaves that travel outward at the speed of light are electromagnetic waves.

•Electromagnetic waves are produced when ripples of electricity are spread out at the speed of light.

The electromagnetic spectrumLike all waves, electromagnetic waves (like light) have frequency, wavelength, amplitude, and speed.

•Also like other waves the energy of, electromagnetic waves are in proportion to their frequency.
•The higher the frequency the more energy an electromagnetic wave has.
•The electromagnetic spectrum almost all electromagnetic waves are invisible.
•The electromagnetic spectrum includes radio waves, microwaves, infrared light, ultraviolet light, X-rays, and gamma rays.

Visible light are the only electromagnetic waves that can be seen by the human eye.
The wavelength and frequency of visible lightThe wavelength of visible light is very small it is measured in nanometers. One nanometer (nm) is one billionth of a meter (10-9 m).
•The frequency of light waves is very high.
•As frequency increases, wavelength decreases.
Energy and color of lightThe energy of waves is proportional to frequency.
•Higher-frequency waves have more energy than lower-frequency waves.
•The same is true of light. Since color is related to energy, there is a direct relation between color, frequency, and wavelength.
The speed of light wavesAll electromagnetic waves travel at the same speed in a vacuum, the speed of •light — 3 × 108 m/sec
•the SPEED of light is the frequency multiplied by the wavelength.

Speed of Light through Matter
Light travels slower through materials (matter)
Index of refraction
• The index of refraction (n) for a material is the ratio of the speed of light in a vacuum to the speed of light in that material.
Low-energy electromagnetic wavesElectromagnetic wave energy is measured by its ability to break chemical bonds.
•Low energy waves cannot break chemical bonds.
•Examples of low energy waves are radio waves, microwaves, infrared waves (heat from sunlight), and visible light.
High-energy Electromagnetic Waves
•High energy waves have the ability to break chemical bonds.
•Ultraviolet rays are an example of high energy rays harmful and can cause sunburn, and cataracts.
•The ozone layer of the earth’s atmosphere serves as protection from ultraviolet waves that come from sunlight.
High-energy Electromagnetic Waves
•X rays are high frequency waves used to see through soft skins layers to bones.
•Gamma rays are used in medical tests, but overuse can be harmful to the human body. Lead shields are needed to block these harmful rays from damaging body tissue.

Lab Activity
http://www.nasaexplores.com/show_912_student_st.php?id=030106134335

Models Of The Electromagnetic Spectrum
Student Sheet(s)

Objective
Students will construct models of the spectrum. Students will learn basic characteristics about the spectrum and the uses and misrepresentation of models.
Background Information
Models are necessary in helping us understand relationships, but they can also be misleading. To use models effectively, it is important to understand how a model may be different from what it represents. Models help us "see" things that are too large for us to see — such as the Milky Way Galaxy — and things that are too small, such as the structure of an atom. Models can also help us understand what happens when the time it takes for things to happen is very long.
All models have distortions. Flat maps of the Earth get more exaggerated towards the edges — putting a round shape onto a flat surface causes some of the countries to look larger than they really are. The larger the concept the model is describing, the larger the amount of distortion in the model. Again, models are still useful because they help us see relationships, and are convenient. A flat map may be folded up and put in your pocket. So there are trade-offs between accuracy and convenience whenever you construct a model.
The model of the electromagnetic spectrum and like all other models contains distortions. The model is extremely useful for showing the frequencies of the different bands of electromagnetic radiation (EMR), and the relationships between frequency and wavelength. However, this is a logarithmic scale, and it distorts the actual width of the different bands of radiation. The result is that looking at this model gives you the wrong idea that the radio band is very large compared to the X-ray band, for example. In Part B, a logarithmic and linear model will be constructed on the same chart and compared.
Electromagnetic spectrum displays the energy and frequency of the wavelengths. Radio waves, television waves, and microwaves are all types of electromagnetic waves. They only differ from each other in wavelength.
Pre-lab Questions
1. Define the following terms: wavelength, crest, trough, amplitude, frequency, and logarithmic.
2. Name another example of a model used in science.
3. List the major regions of the electromagnetic spectrum in order of increasing wavelength.
Part A — Household Materials Model
As a group of two, construct a model representing the electromagnetic spectrum. Your design is open to your own creativity. The materials used must provide an analogy for the different regions of the spectrum. One example would be to use different types of pasta (spaghetti, lasagne, linguini, macaroni, ziti, etc.) to represent the different regions.(Neatness and organization count!)
Your model must:
Clearly characterize each type of EMR
On poster board:
Include an explanation for choosing each material to represent a portion of the spectrum
Make a chart describing at least two human uses of each region of the spectrum
Write an explanation on how your model represents the spectrum
Part B — Logarithmic Versus Linear Scale Model
1. Tape four pieces of 8 1/2" by 11" paper together end-to-end so that their long sides are on the bottom. The pieces of paper should overlap by 3 cm.
2. Then draw a line down the left side of the chart about 2 cm from the edge.
3. From the line you have just drawn, draw two horizontal lines extending to the right across the pages: one line 8 cm from the top of the chart, and the other line 10 cm below the first horizontal line (see diagram below).
4. The top line will be used to plot the logarithmic scale. Along this line, mark off 24 1-cm intervals from the vertical line you drew. Starting at 1 cm, label each interval with increasing powers of ten, from 101 to 1024. These numbers represent the frequency in Hertz of the electromagnetic spectrum.
5. Use the information from the Frequency Range Table below to divide your scale into the individual bands of electromagnetic radiation. (Use the entire visible band, not the individual colors.)
6. Before you can construct the linear scale, it is necessary to convert the frequencies that you used for the logarithmic scale. Those numbers simply told you the range of frequencies, or amount of energy, that each of the bands of EMR covers within the spectrum. Now we want to compare the width of each of the individual bands of radiation relative to each other. We can do this by converting the remaining bands of EMR in the chart above to the same frequency range of 1014. Convert the frequency numbers for all bands (except visible) in the Frequency Range Table above to 1014 and record them in the table. (Reminder moving the decimal to the left increases the power and moving the decimal to the right decreases the power. 3.4 x 105 = .34 x 106)
7. Mark off 10 10-cm intervals from the vertical line. Starting at the first interval, label each mark as a whole number times 1014, from 1 x 1014 to 10 x 1014. Label the bottom of your model "Frequency in Hertz."
8. Now plot some of the 1014 frequencies you calculated on the bottom line of your constructed model. Plot the individual colors of the visible spectrum and color them.
Questions
1. What can be concluded from a comparison of your logarithmic and linear scales?
2. Calculate the width of the X-ray band. How much string would it take to measure the distance from the end of the ultraviolet band to the end of the X-ray band? What do you think you would need to measure the distance to the end of the X-ray part of the EMR? Obtain a map from the Internet or use a local or state highway map to plot this distance. Name the starting point on the map and the ending point.
3. Based on your results for the width of the X-ray band, what would be your estimate for the width of the gamma ray band of radiation? What would you need to measure the distance?
4. How are model helpful and how can they be misleading? Provide one example in your answer. Do not use your spectrum model.
5. Design a concept map showing the regions of the electromagnetic spectrum and the basics parts of a wave.

Videos
PBS Teachers Domain
http://www.teachersdomain.org/resources/phy03/sci/phys/energy/nasaspectrum/index.html
http://www.teachersdomain.org/resources/phy03/sci/phys/energy/emspectrum/index.html

United Streaming
http://streaming.discoveryeducation.com/search/assetDetail.cfm?guidAssetID=cb55a6c8-f37a-4c4a-8f66-ba0d80d1f32c

http://streaming.discoveryeducation.com/search/assetDetail.cfm?guidAssetID=dc20d844-9de5-4617-8a2f-ab0adbbc8bac

Webquests
http://www.haystack.mit.edu/edu/pcr/waves/General%20Wave%20Properties/Electromagnetic%20Spectrum%20Web%20Quest.htm

Simulations
http://www.teachersdomain.org/resources/phy03/sci/phys/mfw/spectrum/index.html

http://www.teachersdomain.org/resources/ess05/sci/ess/earthsys/irgallery/index.html