PHY112 On-line Lab # 9 Radios and Radio Waves
Radios and Radio Waves
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Introduction:
In a previous lab we discussed different types of waves and wave propagation. The physical world is full of examples of wave motion. There are waves on strings, sound waves in air, waves in water and on the ocean, and one of the most important types of waves in the study of physics, Electro-Magnetic waves .
The electromagnetic spectrum covers a huge range of frequencies, everything from super high frequency gamma radiation down to very low frequency radio waves. The E-M spectrum even includes the visible light that our eyes see.
We often depict an E-M wave whether from light, gamma rays, x-rays, or radio waves as a simple sinusoidal two-dimensional wave form like the one below.
However, an E-M wave is actually more complicated than this, and much more interesting too. The Electrical component () and the Magnetic component () of the waves are perpendicular to each other. Take a look at the following gif link to get a more realistic understanding of how E-M waves actually propagate through space.
https://upload.wikimedia.org/wikipedia/commons/9/99/EM-Wave.gif
This lab will primarily be dealing with Radio Waves and how we use them to send and receive information. In Part I of the lab you will be asked to watch a few videos and then comment on what you have learned. In Part II will be using an on-line PhET simulation to “transmit” and “receive” different types of radio signals.
Please watch this first video, it will give you some important background information on our topic. You won’t be asked any questions on it immediately, but please watch it in its entirety as it explains some critical concepts, and we will refer to it later in Part II of the lab.
Part I
Watch the following video and then answer the questions below.
1) What are the three basic types of modulation used in radio transmissions
2) What are the basic functions of a radio Transmitter ?
3) What are the basic functions of a radio Receiver ?
Watch the following video and then answer the questions below.
4) In your own words describe what Amplitude Modulation (AM) entails.
5) In your own words describe what Frequency Modulation (FM) entails.
6) Which one of these two types of radio transmission has the potential to carry a signal the greatest distance and why?
7) What are the several advantages to using Frequency Modulation over Amplitude Modulation for radio transmission?
Part II
Go to the web page:
https://phet.colorado.edu/en/simulation/legacy/radio-waves
In this simulation you will be “transmitting” a radio signal by moving an alternating electrical current along the antenna of a transmitter. The changing current is represented by a single electron that is moved up and down the shaft of the transmitting antenna. A corresponding electron is visible on the shaft of the receiving antenna and will oscillate up and down in response to the propagating E-M signal that it receives.
There are a number of settings that you can try out. We won’t be using them all, however you may want to take some time to explore the possibilities and to familiarize yourself with the simulation settings and controls.
Note: To reset the simulation back to its original state, you will need to use the browser refresh button to reload the page.
First we will observe what happens when we transmit using a simple sinusoidal wave. To do this click on the oscillate option on the right side of the screen in the Legend.
1) What differences do you notice about the Transmitting electron and the Receiving electron?
2) Now check the electron position box at the very bottom of the legend. Then answer the following:
Describe what you observe in terms of amplitude and timing of the electron positions. What does this mean in a practical sense for the person who is listening to the radio receiver as compared to the person who is broadcasting? In the real world, how fast is the radio signal propagating?
3) Now uncheck the electron position box in the legend.
Next select the Full field option, the Electric field option, and the Radiated field option in the legend.
The green arrows represent the direction and the strength of the electric field produced by the transmitter at specific times and at specific points in space. Think back to the video that you watched in the introduction to the lab. The one that talked about “kinks” in the electromagnetic field. In your own words explain what you observe in the simulation in terms of what you learned in that video (hint: the video discussed “old” and “new” fields).
4) Now click the browser refresh button to reload the page.
We will be simulating sending an AM radio signal.
Set the transmitter to Oscillate.
In the legend you will slide the Amplitude selector back and forth. Try moving it at different rates and different distances so as to visibly effect the form and size (amplitude) of the radio signal.
Describe your observations below. How much variation can you get in the wave form?
How quickly does the wave change form in response to your movements?
5) Now click the browser refresh button to reload the page.
We will be simulating sending an FM radio signal.
Set the transmitter to Oscillate.
In the legend you will slide the Amplitude selector back and forth. Try moving it at different rates and different distances so as to visibly effect the form and size (amplitude) of the radio signal.
Describe your observations below. How much variation can you get in the wave form?
How quickly does the wave change form in response to your movements?
6) Which of the two methods of transmitting information via radio signal seemed to give the most responsiveness and range of variability AM of FM?
7) Think back to the videos that you watched in Part I of the lab. How does this simulation corroborate what you learned with regard to the amount of information that can be transmitted by each of the two systems?
Part III
Of course, humans use radio wavs to communicate, as we have just discussed. But radio waves occur naturally and literally permeate all of space. Scientists, by using and detecting radio waves have made some truly amazing discoveries about our universe.
Here is a short video to watch that deals with just a few examples of this.
After watching the video, do a little research of your own then list and briefly describe two or three other important scientific discoveries that have been made possible through the use or observation of radio waves.
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