Now investigate the electric fields produced by infinitely long lines of charge. These applets have the same source configurations as in the electric field lesson, except that the sources are lines of charge rather than point charges. (This lends itself more easily to our two-dimensional treatment.) You can draw field lines as before (right-click or clover-click), and now you can also draw Gaussian surfaces:
All the Gaussian surfaces are one unit high and are drawn in green. What do you observe about the electric flux through a closed surface?
The next few demos are like the previous ones, except that the sources are no longer infinitely thin. They are cylinders (usually 40 pixels in radius) and have a uniform charge density. Each cylinder has the same total charge-per-unit-length as its counterpart above. And as above, red indicates positive charge, and blue indicates negative charge.
I suggest you use the rectangle tool (shift-left-drag) to surround one half or one quarter of a cylinder. Explain the result you get.
Fans of vector calculus can also change the field arrow into a curlmeter (control-right) or a divergence meter
(shift-right). What do you observe? (Need help remembering all these
mouse
commands)
How does the Gauss integral depend upon the size and shape of the Gaussian surface? What does it depend upon?
Why does the electric field outside a charged cylinder behave like the field outside a line of charge? What about inside the cylinder?
What is the Gauss integral if the loop surrounds half of a charged cylinder? What about a quarter of the cylinder?
Look at one of the examples with a single cylinder. Where is the field strongest? Where is it zero? Is this what you expected?
Once you've finished here, find someone to work with and try out more interactive applets.