, J (vector
) is equal to the sigma sum
of all k for qk
(vector), where q is the charge
of the k particle
, m is the number of k particles in a volume
, and F is the flux
of the k particles through the volume. The dot product
of J and the area
vector is equal to I
, the current
. A scalar
J can be defined as current/area.
Also a source of boundless merriment in Physics 16, Winter 2001 term, at Dartmouth College. As the great Professor Gleiser was talking about J, saying stuff like "J is pointing in this direction" and "J is very large", a group of cohorts and I were holding back laughter...as I myself am a very large J(ay). When the Professor stopped to ask what was so funny, we told him. From that point on, whenever he was about to do something with current/area value, he'd say something to me first, such as, "Jay, I need you to stay constant in time", or when he was differentiating "J", he wrote the standard dJ/dt on the board and remarked, "Hey, Jay, you've got a second job now, you're a DJ now!" I only wish it were that much fun when we got to relativity.