Learning Center
Plans & pricing Sign in
Sign Out

Exploring the


									     Exploring the
Electromagnetic Spectrum

      Mrs. Sandra Landwersiek
       Physical Science Class
              7th Grade
         Sacred Heart School
             Spring 2005
                          Objectives of Unit:

Students will know
      Electromagnetic Waves have unique traits
      EM wave uses have increased in past 100 years
      Visible Light is reproduced by technology in many forms
      Visible Light interacts with materials

National Science Education Standards Addressed:
A.2-8, A.9.a-f, B.3.c, B.3.f, F.5.c

Textbook used: Physical Science by McDougal Littell, 2005 Edition for
Middle School Science

                                 Day 1: Pre-test
                            Electromagnetic Waves
                                 Diagnostic Test

Choose the letter of the best answer

_____ 1. A mechanical wave always transfers energy
            a. through a medium
            b. through outer space
            c. in a vacuum
            d. without causing any matter to move

_____ 2. Which of the following statements is true?
            a. All waves transfer matter through some type of medium.
            b. All waves, including mechanical waves, transfer energy.
            c. All waves require a medium through which to move.
            d. All waves can transfer energy through empty space.

_____ 3. The distance between two crests of a wave is the wave’s
             a. amplitude
             b. frequency
             c. speed
             d. wavelength

_____ 4. The frequency of a wave is measured in
             a. meters per second
             b. hertz
             c. millimeters
             d. seconds

_____ 5. Jenna uses an instrument to measure how many wavelengths pass her in
                 1 second. She is finding the wave’s
             a. amplitude
             b. frequency
             c. speed
             d. wavelength

_____ 6. Gregg knows the frequency of a wave. To find the speed of the wave, he needs
         to know its
             a. amplitude
             b. energy
             c. intensity
             d. wavelength

_____ 7. Two waves have the same speed. Wave A has a longer wavelength than wave
         B. Which of the following statements is true?
            a. Wave A has a lower frequency than Wave B
            b. Wave B has a lower frequency than Wave A
            c. Wave A and Wave B have the same frequency
            d. You cannot tell which wave has higher frequency

_____ 8. Sean puts a board with a gap in it into a tank of water. Then he causes waves to
         travel toward the board where the gap is. What happens to the waves when
         they reach the board?
             a. They will pass through the gap without being affected.
             b. They will be completely reflected from the board.
             c. They will be refracted as they pass through the gap.
             d. They will be diffracted as they pass through the gap.

_____ 9. Reflection happens when a wave
             a. enters a new medium at an angle
             b. passes through a narrow gap
             c. moves around a solid object
             d. hits a barrier it cannot pass through

_____ 10. The energy that a mechanical wave moves from one place to another is
            a. potential energy
            b. kinetic energy
            c. thermal energy
            d. chemical energy

_____ 11. The speed of any mechanical wave is affected by
            a. its amplitude
            b. the amount of energy it carries
            c. the medium through which it travels
            d. its diffraction

_____ 12. Sound travels faster in materials that are
            a. colder
            b. denser
            c. less elastic
            d. lighter

             Day 2: Introduction and Demonstration

  I. All EM waves have unique traits
         a. Introduction
                 i. What EM waves are
                ii. How they form
               iii. Sources
               iv. Speed
         b. Demonstration:

      Demonstrate how EM waves travel in straight lines and can be reflected back

      Use a remote controlled devise such as CD player or VCR,
       portable radio, mirrors, laser penlight, and umbrella lined
       with alum foil.
      IR waves--practice using remote control aiming at a mirror
       to turn device on.
      Visible light--using multiple mirrors reflect laser beam
       back and forth.
      Radio waves-- tune radio to weak channel using umbrella as large dish receiver
       reflecting waves back to radio. Also try using mirrors to reflect back to antennae .

                      Day 3: Discussion & Activity
  II. EM waves uses have increased in past 100 years
        a. Intro second section of textbook
                i. Radio, TV, Cordless phones
               ii. Microwave ovens, radar, cell phones
              iii. Infrared heat, toasters, curling irons, remote controls
              iv. UV sterilization, medical uses
               v. X-ray, medical and industrial uses
              vi. Gamma rays, medical and astronomical uses
        b. ACTIVITY use of microwave oven to calculate speed of light

           Finding the Speed of Light with Marshmallows


      Microwave                                        Microwave Safe Dish
      Jumbo Marshmallows                               Ruler

Intro-Mapping the Energy Nodes

Microwave ovens cook unevenly because a pattern of standing waves that form inside the
oven chamber. The pattern creates an array of hotspots throughout the oven’s volume. An
operating frequency of around 2000 MHz will produce a wavelength of around 10cm,
and the hotspots should be at half-wave points, or every 5cm, but in a complex 3D


   1. First open the marshmallows and place them in the casserole dish, completely
      covering it with a layer one marshmallow thick. Make sure that the flat side of the
      marshmallow is facing upwards.

   2. Take the turntable out of the microwave

   3. Next put the dish of marshmallows in the microwave and cook on low heat. The
      microwave will not cook evenly after the removal of the turntable and the
      marshmallows will begin to melt at the hottest spots in the microwave.

   4. Heat the marshmallows until they begin to melt in 4 or 5 different spots

   5. Remove the dish from the microwave oven and observe the spots

   6. Take the ruler and measure the distance between the melted spots. You will soon
      find that one distance repeats over and over. This distance will correspond to the
      wavelength of the microwave. That should be a little over 12 centimeters.

   7. Now, turn the microwave around and look for a small sign that tells you the
      frequency of the microwave. Most commercial microwaves operate at 2450 MHz.

     Note: Only do one trial. Obtain the wavelength data from other
   groups. If no frequency is visible on the microwave, use 2450 MHz.
       Measuring the Speed of light with Marshmallows:

Data Table:

   Group          Wavelength         Frequency, f     Velocity, v   % Error
                     (m)                 (Hz)           (m/s)

Show Sample Calculations:

Determine the % error for each group below:

     Actual speed of light = 3.0 x 10 8 m/s

     % Error = [ (Actual – Experimental) / Actual ] x 100

Discuss possible sources of error in your measurements:

                     Day 4: Discussion & Activity
   III. Visible light is reproduced by technology in many forms
           a. Introduce third section of textbook
                     i. Incandescence, fluorescence, luminescence, and bioluminescence
                    ii. LED
           b. Use incandescent, halogen, and fluorescent bulbs in small lamp to show
   differences of “light” on objects, go outside and use sunlight for control

   Incandescent                                                              Fluorescent

                  Day 5: Discussion & Demonstration
   IV. Visible light interacts with material
           a. Discuss the following topics
                    i. Transmission, absorption, reflection
                   ii. Wavelength, primary colors and primary pigments
                  iii. Polarization and scattering
          b. Demonstrate visible light and laser polarization/cancellation

      1. Use a flashlight and laser penlight through various polar lenses to show the
         path and eventual cancellation of path of light rays.
      2. This can demonstrate the synchronization of laser waves

                         Day 6: Internet Activity
   V. Wrap-up activity researching Internet for new/specific uses of various EM waves
         a. Scavenger hunt on internet for uses for each wave region

           b. Student with most uses overall, most in category, most novel (certified
              with sources) win prizes.
                  i. Radio and microwave can be combined
                 ii. “Medical Uses”,” Military Use”, or “Industrial Use” have to be
                     specific in naming exact use
           c. Sources have to be kept of each use, with emphasis on reliable sites

                 Uses of the Various Types of EM Waves


Type of EM Waves                 Uses                                Sources

                                 Day 7: Post-test
                            Electromagnetic Waves
                                     Key Concepts

Choose the letter of the best answer (5 points each)

_____ 1. Unlike mechanical waves, electromagnetic waves can transfer energy
         a. through empty space
         b. at a high speed
         c. without a field
         d. from air into water

_____ 2. The Sun is the source of
         a. all EM waves on Earth
         b. most EM waves on Earth
         c. only a few EM waves on Earth
         d. no EM waves on Earth

_____ 3. An EM wave is caused by the vibration of
         a. air particles
         b. electric and magnetic fields
         c. a vacuum
         d. water in an object

_____ 4. Which of the following shows EM waves in order from lowest to highest
           a. gamma rays, microwaves, radio waves
           b. microwaves, x-rays, visible light
           c. infrared light, ultraviolet light, gamma rays
           d. ultraviolet light, radio waves, x-rays

_____ 5. The heat of a toaster is transferred by
         a. infrared light
         b. radio waves
         c. visible light
         d. x-rays

_____ 6. Bioluminescent animals produce light by
         a. becoming hot enough to glow
         b. absorbing and emitting radiation
         c. emitting electronic signals
         d. using chemical reactions

_____ 7. Which of the following produces incandescent light?
         a. A firefly
         b. a fluorescent bulb
         c. a halogen bulb
         d. an LED

_____ 8. Most of the light that hits a translucent material
         a. passes straight through the material unchanged
         b. is transmitted and spreads out in all directions
         c. is reflected and does not pass through
         d. is absorbed and does not pass through

_____ 9. Light waves that pass through a polarized filter
         a. have their electric fields vibrating in one direction
         b. change in wavelength and frequency
         c. are diffracted by the filter and spread out
         d. are refracted and show a spectrum of colors

_____ 10. If you hold a white piece of paper in a blue light, the paper appears blue
because it
           a. reflects blue light and absorbs other wavelengths
           b. scatters blue light more than other wavelengths
           c. reflects all the wavelengths of light that are shining on it
           d. absorbs all wavelengths of light and emits blue light

                               Interpreting Visuals

Using the diagram, answers the following questions

11. Circle the letter for each of the following kinds of waves. (3 points each)

       gamma rays              A      E       G
       infrared light          C      E       G
       microwaves              B      D       F
       radio waves             A      C       F
       ultraviolet light              B       E       G
       visible light           C      D       E
       x-rays                  A      D       F

12. Which electromagnetic waves have the highest frequency? (3 points each)

13. Which electromagnetic waves transfer the least amount of energy? (3 points each)

14. Compare infrared light and ultraviolet light. Which has a longer wavelength? How do
   know? (3 points each)


                              Reading in the Science

Using the passage, answer the following questions. (4 points each)

               Electromagnetic waves can travel great distances across empty spaces.
               move at a constant speed on about 300,000 km/s. This constant speed
               that scientists can measure distances by finding how long it takes light to
              that far. Some of the most distant objects observed are about 13 billion
light-                 years away.. This means that light takes 13 billion years to travel
from these                    objects to Earth. These objects give off large amounts of
EM radiation. However,
              they are so faint that they can be detected from Earth only by using the
              powerful telescopes.

15. According to the passage, how can scientists use light waves to find the distances to

16. Radiation from a distant star is very strong at the star. However, it is very faint by the
time it
   reaches Earth. What do you think happens to the radiation as it moves through space
that might
   explain this?

Extended Response:

Answer the following questions. (6 points each)

17. Comparing and Contrasting: Compare and contrast incandescent and fluorescent
lighting. How
   are they similar? How are they different in the way they produce light?

18. Contrasting: What happens when you mix all three primary colors of light in equal
   What happens when you mix all three primary pigments in equal amounts? What
explains the
   difference? Think about how each group combines to make other colors. Does mixing
add or
   subtract wavelengths?


To top