Applied Science - Physics (5A)
Pre Lab 

   
OBJECTIVES:
  • Investigating different types of waves.
  • Distinguishing between electromagnetic and physical waves.

VOCABULARY:

  • electromagnetic
  • energy
  • physical
  • transverse
  • wave
MATERIALS:

Students compare physical with electromagnetic waves..

BACKGROUND:

There are many waves generated by the release of energy but the two major types of waves are physical and electromagnetic. Physical waves need a medium to go through, and electromagnetic can go through many substances including a vacuum. 

The more students review the different types of waves, the easier it will be for them to recognize the differences. You will be demonstrating the 2 major types of waves: electromagnetic and physical.  To illustrate this to students explain that  sound is a physical wave, and light, microwaves, television and radio waves are all electromagnetic.

The term "wave" refers to both physical and electromagnetic. The different components include; the crest (top of a wave); trough (bottom of the wave); wave height (how high is the crest); and wavelength (distance from crest to crest or trough to trough). These terms even apply to the waves produced in oceans.

Waves are essentially a way in which energy can be transferred from one place to another. These concepts will be developed in high school physics.

PROCEDURE:

  1. Discuss with students the components of a wave, whether physical or electromagnetic. Go over crest, trough, wavelength, and wave height, defined by the figure to the right.
      
  2. Explain that there are two major types of waves, physical and electromagnetic.
      
    Physical waves must have a medium to transfer energy, like water, a rope, or a slinky. An electromagnetic wave can go through a vacuum, like light or x-rays.
      
  3. Demonstrate a physical wave by using a slinky. One student holds a slinky on one end. The teacher stretches the slinky about 2-3 feet. The teacher will transmit energy by pulling back several of the coils and then releasing them. The movement will be a push-pull or compressional wave. Instruct students to record what they see.
      
  4. Demonstrate another example of a physical wave using a rope. Tie the rope to something stationary. From the opposite end, one student will hold the loose end of the rope and transmit energy by snapping his wrist toward the stationary end of the rope. Have students record the movement of the rope. This illustrates transverse (or shear) waves, a physical wave.
      
  5. Using an eyedropper and a pan of water, drop water into a pan of water very slowly. Record the movement of the water's surface. These are physical waves.
      
  6. If you have a radiometer, place it in the sun. Record what happens. Notice that the black and white panels move around. The electromagnetic waves of light are hitting the white panel and pushing the panels. It also demonstrates that light waves have a physical component, pushing is a mass effort. The mass of the light waves reflecting from the white surface cause kinetic energy derived from the potential energy.
      
  7. Turn a radio on, and ask students where is the music coming from. Turn it off. Why doesn’t the room fill with music if radio waves are all around? The radio concentrates radio waves. Make sure the students realize that the sound produced is not the actual radio waves.
      
    Conclude that electromagnetic waves can travel through a vacuum and physical waves cannot. Sound waves are visible and some electromagnetic waves are invisible.

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