Using the Mouse Buttons in the Field Applets
The electric and magnetic field applets use every possible combination of mouse buttons and modifier keys (these are sometimes calledchords ) to do interesting things. There are too many of them to list in each module, so the complete list is here for easy reference. You may want to open this page in another browser window in order to keep it visible. But after a while, using the chords will come to seem as natural as falling off a bicycle or using Emacs.
Not all of these chords will work in every instance of a field applet. Sometimes capabilities are disabled because they are inappropriate or even incorrect for a lesson or a particular field. You shouldn't worry about this.
How Many Buttons Have You Got?
You must realize that not all mice have the same number of buttons. The table below assumes that you have a three-button mouse, as is found on most Unix workstations. If you are using a PC, you should have a two-button mouse. In that case, to simulate the middle button, you should use the left button while holding down the ALT key. If you are using a Macintosh, you should have a one-button mouse. In that case, the single button corresponds to the "left button" in the table. To simulate the middle button, use the single button while holding down the ALT (OPTION) key, and to simulate the right button, use the single button while holding down the COMMAND (clover) key. To summarize:
Mouse Buttons Unix Left Middle Right PC Left Alt-Left Right Mac Button Option-Button Clover-Button
On a Unix workstation, you can, if you want, use Alt-Left in place of Middle, and Meta-Left in place of Right. On all three types of machines, you can, by judiciously combining modifier keys and mouse buttons, make the program think you have simultaneously pressed both the right and middle buttons. The program will then perform both actions.
Play Those Funky Mouse Chords
A chord consists of a mouse button and possibly either or both of the shift and control keys. There are therefore twelve distinct chords. Since the mouse buttons may be simulated with other modifier keys, you could be using three or four (for a Right+Middle double chord) modifiers at a time. It's actually kind of fun.
- Field Indicators
- Watch the field arrow as it grows and shrinks. Notice that the coordinates are given in your browser's status box (which is usually in the lower left-hand side of the browser window).
- To drop a field arrow, shift-control-alt-left click (or S-C-middle).
- To lay down an array of arrows, hit "A".
- To change the field arrow into a curlmeter, control-right drag. See how it twists (watch the red arm). The curlmeter twists clockwise when the curl of the field is into the page, and counterclockwise when the curl is out of the page. (These are the only possible directions for the curl in these applets.)
- To drop a curlmeter, control-alt-left click (or control-middle).
- To lay down an array of curlmeters, hit "C".
- To change the field arrow into a divergence meter, shift-right drag. See how it bows in where the divergence is negative and out where the divergence is positive.
- To drop a divmeter, shift-alt-left click (or shift-middle).
- To lay down an array of divmeters, hit "D".
- Field Lines
- To draw a field line, click the right button. The rainbow of color along the line indicates the strength of the field; red is strong, and blue is weak.
- To draw an equipotential (cyan), click the middle button.
- To draw both, use the modifier keys to simulate clicking both right and middle.
- Loops and Surfaces
- Draw an orange loop:
The applet calculates and prints the line integral of the field around the loop. The direction of integration is always counterclockwise.
- To draw a rectangle, left drag.
- To draw a circle, control-left drag.
- Draw (the footprint of) a green Gaussian surface:
The applet calculates and prints the surface integral of the field through the surface. The surface has a height of one unit.
- To draw a rectangle (box), shift-left drag.
- To draw a circle (cylinder), shift-control-left drag.
- To erase the loop or surface and the integral, click the left button again.
- Erasing
- To erase the lines and laws, hit "E", backspace, or delete.
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