The electric and magnetic field applets use every possible
combination of mouse buttons and modifier keys (these are sometimes called
chords) 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.
- 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:
- To draw a rectangle, left drag.
- To draw a circle, control-left drag.
The applet calculates and prints the line integral of the field around
the loop. The direction of integration is always counterclockwise.
- Draw (the footprint of) a green
Gaussian surface:
- To draw a rectangle (box), shift-left drag.
- To draw a circle (cylinder), shift-control-left drag.
The applet calculates and prints the surface integral of the field through
the surface. The surface has a height of one unit.
- 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.