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Radio Wave: Definition, Spectrum & Uses

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  • 0:04 What Is a Radio Wave?
  • 2:12 How Are Radio Waves Generated?
  • 3:08 Uses of Radio Wave
  • 5:09 Lesson Summary
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Lesson Transcript
Instructor
Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Expert Contributor
Elaine Chan

Dr. Chan has a Ph.D. from the U. of California, Berkeley. She has done research and teaching in mathematics and physical sciences.

Radio waves are used in almost all forms of wireless communication, and you certainly utilize them every day! In this lesson, learn more about how radio waves are produced, and then learn about the different types of radio waves and how they are used.

What Is a Radio Wave?

When you get in your car, you probably expect to be able to listen to the radio, right? There are many stations that you can tune your receiver to, and each one picks up different radio signals. Radio waves have been an important part of our lives for many years, providing entertainment and communication capabilities for millions of people throughout the world, and even a few out in space! How does this all work? What are radio waves, and how are they generated, transmitted, and received?

Radio waves are electromagnetic waves, which means that they are made up of an oscillating pattern of electric and magnetic fields that travels through space. Radio waves are certainly not the only type of electromagnetic wave, however. Light, microwaves, gamma rays, and many others are also electromagnetic waves, and together, they make up what we call the electromagnetic spectrum.

Even though light and radio waves may appear different to us, all electromagnetic waves are actually quite similar. The difference between a light wave and a radio wave is that these two waves have different wavelengths and frequencies. The frequency of a wave is how many times it repeats in a certain time interval (usually one second), and wave frequency is usually measured in units of Hertz (Hz). One Hertz corresponds to one wave cycle every second.

Light waves fall towards the middle of the spectrum, while radio waves are electromagnetic waves that have the much lower frequencies. Radio waves have frequencies that range from 3 kHz up to 300 GHz, while the frequency of visible light ranges from 400,000 to 700,000 GHz.

Just like all electromagnetic waves, radio waves can travel long distances through all kinds of media, or even through empty space. They also travel really fast, moving at the speed of light. Because of this, radio waves are critically important for all kinds of communication technologies, and not just important for keeping you entertained on a long drive in your car. Radio waves are used for everything from transmitting music and videos to communicating with astronauts in outer space.

How Are Radio Waves Generated?

Radio waves exist in nature all around us, although we didn't know they were there until they were first detected by Heinrich Hertz in the late 1800s. Any time there is a fluctuation in an electromagnetic field, electromagnetic waves are generated, and many times these are radio waves.

Electrical appliances generate radio waves all the time, and so does lightning. Even planets and stars are constantly sending out radio waves. Scientists measure these to learn more about distant celestial objects. This is an area of science called radio astronomy.

Although radio waves are produced naturally, we can also produce radio waves with very specific frequencies and use them to transmit information. Radio waves are generated by turning a signal, like the sound of a voice, into a series of radio wave pulses. These waves travel through the air until they hit a receiver, which decodes the wave pulses and turns it back into sound.

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Additional Activities

Radio Waves Questions

  1. Which type of electromagnetic wave can travel furthest through space, without being absorbed?
  2. What polarity is the electromagnetic wave?
  3. How are radio waves transmitted and received?
  4. Do mobile phones use radio waves or microwaves?
  5. What are the sources or radio waves coming in from outer space?


Answers

1. Radio Frequency.

All electromagnetic radiation from space cannot reach the surface of the Earth, although RF, visible light and some UV can. Astronomers can observe infrared using telescopes placed on mountains. Multiple dishes can be arranged to magnify the signal received in radio telescopes.


2. It depends on how it was transmitted.

An electromagnetic wave consists of oscillating electric and magnetic fields, always perpendicular, traveling in the direction perpendicular to both the electric and magnetic fields. In linear polarization, the fields oscillate in one direction. In circular or elliptical polarization, the fields rotate at a constant rate in a plane as the wave travels. The rotation can have two possible directions. Right circular polarization is when the fields rotate in a righthand sense with respect to the direction of wave travel. If the fields rotate in a lefthand sense, it is left circular polarization.


3. Antennas help control transmission and detection of electrical energy to and from RF waves. Antenna dimensions must generally be comparable to wavelength. The length of the antenna is related to the wavelength of the wave it can receive or transmit. If receiving linearly polarized waves, you may want two receivers (dipole or rod configuaration) at right angles. With circularly polarized antennas, you may need left and right circularly polarized helically shaped antennas. The dish is used in radio telescopes and other devices. The geometry of the parabolic dish is such that a wave coming from infinity and parallel will be reflected to the focal point.


4. Both, since microwaves are classified as radio waves.

Cell phone frequencies are in the radio frequency region of 300 MHz to 300 GHz - which are microwaves. They are also radio waves.


5. Planets, stars, gas and dust clouds, galaxies, pulsars and black holes.

Radio telescopes can also detect quasars, which is short for quasi-stellar radio source. Some quasars emit 1,000 times as much energy as the entire Milky Way.

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