# physic5..slpElectromagnetic Waves and Maxwell’s Equations

For this module, you will investigate the operation of antennas. Antennas can both transmit and receive electromagnetic waves. You see antennas everywhere from portable radios and cell phones to radio transmission and cell network towers. In this laboratory, you will look at two types of antennas, a Linear Antenna (End-Fed) and a Linear Antenna (Center-Fed). Experiment with the simulation by changing the wavelength control (that is, the length of the antenna) and observe the changes in results.

• Linear Antenna (End-Fed) shows the magnetic field near a half-wave linear antenna fed from one end. You can vary the length of the antenna using the “Length” slider.
• Linear Antenna (Center-Fed) shows the magnetic field near a full-wave linear antenna fed from the center. You can vary the length of the antenna using the “Length” slider and you can vary the separation between the two halves of the antenna using the “Feed Separation” slider.

In terms of results:

The Show Intensity checkbox determines whether to show the wave intensity, or the waves themselves. When this is unchecked, the positive wavefronts are shown in green, and negative in red. Viewing the waves (instead of the intensity) only works well when zoomed in, using a low frequency; otherwise the individual waves are too small to see.

The Show Graph checkbox shows the current distribution along the antenna (for linear antennas) or the excitation coefficients (for arrays). The phase is indicated using different colors.

The Show Info checkbox can be used to turn off the information shown in the lower-right hand corner for some antenna setups.

The Stopped checkbox stops the applet, in case you want to take a closer look at something, or if you want to work on something with the mouse without worrying about it changing out from under you.

The Alternate Rendering checkbox is used to speed up rendering, but it actually slows things down on some machines.

The Speed slider controls how far the waves move between frames.

The Zoom Out slider zooms out when you slide it to the right. This slows things down quite a bit.

The Resolution slider allows you to speed up or slow down the applet by adjusting the resolution; a higher resolution is slower but looks better. Also, increasing the resolution acts like zooming out.

The Source Frequency slider controls the frequency of the signal.

The Brightness slider controls the brightness, just like on a TV set. This can be used to view faint waves more easily.

Click on link 1 to access the simulation. If you need the Java plug-in to view the applet, download the plug-in at link 2. (By the way, link 2 contains a lot of really cool applets.) Sources 1 and 2 below are listed as 7 and 8 on the list of required readings and sources in this Module’s Background Information section.

Write a two to three page paper discussing your observations in terms of what you learned about electromagnetic waves and antennas by comparing the results using the Linear Antenna (End-Fed) with the Linear Antenna (Center-Fed).

Required Readings and Sources

1. Falstad, P. (n.d.) Antenna simulation. Retrieved on March 1, 2008, from http://www.falstad.com/antenna/directions.html

2. Falstad, P. (n.d.) Java plugin. Retrieved on March 1, 2008, from http://www.falstad.com/mathphysics.html

## SLP Assignment Expectations:

In general, SLPs are expected to possess the attributes of precision, clarity, breadth, depth, and applicability. Not all of these are relevant to the answer to every problem in the SLP. When it is relevant, the evidence for each attribute is as follows.

• Precision: Numerical answers are calculated correctly, to the correct number of significant figures. When a simulation is used, the results are accurate.
• Clarity: The problem is restated in its simplest form. Relevant variables are identified. Formulas are algebraically rearranged, as necessary. All the mathematical steps are shown, in logical order.
• Breadth: Where discussion is required, the question is placed in context. Alternatives are considered.
• Depth: Where discussion is required, the question is examined in detail. No relevant aspect of the question is omitted.
• Applicability: When required, the practical importance of the principle or phenomenon is accurately described