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Wave Blockers

Difficulty
Time Required Very Short (≤ 1 day)
Prerequisites None
Material Availability Readily available
Cost Low ($20 - $50)
Safety No issues

Abstract

What do the radio, TV, radio controlled cars, and cell phones all have in common? They all use invisible waves to transmit information. Find out which materials block radio waves, and which materials allow radio waves to pass through by doing this experiment.

Objective

Test different materials to see if they block radio waves.

Credits

This project was adapted from a student project submitted to the Marin County Science Fair in California.

Sara Agee, Ph.D., Science Buddies

Cite This Page

MLA Style

Science Buddies Staff. "Wave Blockers" Science Buddies. Science Buddies, 6 Oct. 2014. Web. 25 Nov. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/MatlSci_p036.shtml>

APA Style

Science Buddies Staff. (2014, October 6). Wave Blockers. Retrieved November 25, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/MatlSci_p036.shtml

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Last edit date: 2014-10-06

Introduction

What do the radio, TV, radio controlled cars, and cell phones all have in common? They all use invisible waves to transmit information. These waves, called radio waves, are a type of electromagnetic radiation. Radio waves are not harmful, in fact they are an extremely useful method of global communication. Two essential components for this type of communication are a transmitter and a receiver (PBS, 1998):

  • Transmitting Antenna (transmitter) - A radio signal from a device travels to the transmitting antenna. The signal creates a corresponding electromagnetic field called a radio wave. This radio wave moves outward in all directions from the transmitting antenna.
  • Receiving Antenna (receiver) - A receiving antenna picks up the the radio wave. If the receiving antenna is far away from the transmitter, the signal is very weak.

The ability of a wave to travel through a material is called transmittance, and materials can be divided into good transmitters and poor transmitters. One very good transmitting material for radio waves is the air in our lower atmosphere, which is why radio waves can be transmitted through the air over very long distances. One poor transmitter is the ionosphere of the earth, the uppermost layer of the earth's atmosphere which contains high energy, ionized radiation from the sun. Radio waves that are reflected by our ionosphere stay within the inner atmosphere of the earth, as shown in Figure 1, below. This phenomenon is what makes radio waves so great for global communications, because radio wave signals stay close to the surface of the earth:

image of the ionosphere and radio waves

Figure 1. This figure shows how the upper layers of the earth's ionosphere (composed of the D, E and F layers) reflect and propagate radio waves transmitted from an AM radio antenna. (image © 2007, Thompson Higher Education)

Like the earth's ionosphere, being a poor transmitter is not always a bad thing. Materials which are poor transmitters are sometimes useful because they can block radio waves from moving through them and become insulators. One way to test different materials is to use a radio controlled (RC) car. You will wrap the RC car remote control, the transmitter, with different materials to find out which materials block radio waves, and which materials allow radio waves to pass through. Which materials make good or bad transmitters?

Terms and Concepts

  • Radio waves
  • Electromagnetic waves
  • Transmission
  • Transmitter or transmitting antenna
  • Receiver or receiving antenna
  • Ionosphere
  • Faraday cage

Questions

  • How are radio waves transmitted and received?
  • Which materials block radio waves?
  • Which materials allow transmission of radio waves?

Bibliography

  • Read this tutorial on the transmission of radio waves, or if you have Shockwave you can try the Radio Transmission Activity from PBS:
    PBS, 1998. "A Science Odyssey: You Try It: Radio Transmission," PBS Online, WGBH: Boston, MA. Retrieved June 6, 2007 from http://www.pbs.org/wgbh/aso/tryit/radio/#
  • You can read about radio waves in this Wikipedia article:
    Wikipedia contributors, n.d. "Radio waves," Wikipedia, The Free Encyclopedia. Retrieved June 6, 2007 from http://en.wikipedia.org/w/index.php?title=Radio_waves&oldid=162535596
  • Here is a brief discussion about the transmittance of radio waves vs. light waves:
    NEWTON, n.d. "Ask A Scientist: Radio Wave Transmittance," NEWTON Ask a Scientist Program, Argonne National Laboratory, Division of Educational Programs, Chicago, IL. Retrieved June 6, 2007 from http://www.newton.dep.anl.gov/askasci/phy99/phy99245.htm

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Materials and Equipment

  • Radio controlled (RC) car and controller, both with fresh batteries. You can purchase one from a toy store or from online suppliers such as Amazon.com.
  • Different materials to test:
    • Aluminum foil
    • Plastic wrap
    • Paper
    • Wax paper
    • Cotton
    • Rubber gloves
  • A wide open space to test drive your RC car
  • Lab notebook

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Experimental Procedure

  1. Wrap the RC car remote control in the first material you want to test, using multiple layers so that it is completely and securely covered.
  2. Attempt to operate the RC car using the remote control. Does it work?
  3. Repeat this process for each different material, collecting data in a data table:
Name of Material Does the Car Work? (Y/N) My Observations:
Aluminum Foil    
Cotton    
Paper    
Etc...    
  1. Divide the materials into good and bad transmitters based upon your results.

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Variations

  • Use a stop watch to time your test drive over a set distance. Compare the average time for remote controls wrapped in different materials. Do some go faster or slower? What might this tell you about the transmission of the radio signal?
  • You can do a similar experiment using other remote control devices, like your TV or stereo remote. How do different devices respond? Do you think they use similar or different types of waves?
  • For an advanced project, try broadcasting different frequencies from an old HAM radio. Wrap a receiver with different materials and compare transmittance at different frequencies. Do different frequencies pass through better than others?

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Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

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