Recent content by daviddeakin

Ah, so my mistake was to say "the charge at a given point", when it should be "the charge that has passed a point", which of course can accumulate indefinitely!

This is a question that has kept me awake, trying to rationalise it: Current is rate-of-change-of-flux (or charge if you prefer, which is the same thing): i = dQ/dt Therefore, flux or charge is the time integral of the current. Q = ∫i dt Therefore, if you have a direct current, does...

The amount of charge passing a point in the wire in time t: Q = NqvtA N = electron concentration q = electron charge v = drift velocity t = time A = cross-sectional area So: v = Q/(NqtA) But current is: i = Q/t so substitute this in: v = i/(NqA)

I don't think it's statcoulombs- they're for the cgs system. Note that it says the flux is in coulombs for the SI system. I can see this is going to keep me awake for a while.EDIT: I emailed my lecturer about it, and he said: "It's the same. Intergral of _D_ is charge and integral of _E_ is...

There's definitely nothing else at the end of sentence! The whole book (and indeed my lecture course) follows the same lines- flux is in coulombs. See Wiki, for example: http://en.wikipedia.org/wiki/Statcoulomb "An electric flux (specifically, a flux of the electric displacement field D) has...

Hmm, I've been learning from a book which says: "Gauss' law states that the flux through any closed surface is equal to the charge enclosed by that surface." So I have been using flux in coulombs... What am I missing?

Is (##\Phi##) the flux in coulombs? If so then (##\Phi_E##) would be the force between the plates wouldn't it?

Intriguing! So the top and bottom capacitors are: C=εA/d = 4 x 8.85x10-12 x 2.0x10-4 / 4x10^-5 = 177pF The middle capacitor is: C=εA/d = 8 x 8.85x10-12 x 2.0x10-4 / 4x10^-5 = 354pF The total capacitance is: 70.8pF Charge on the top and bottom plates is: Q = CV = 70.8pF x 3V = 212.4pC...

Hi Gneill, I have difficulty getting to grips with charge! If the top plate has some positive charge, then the bottom plate must have some equal negative charge. But the ones in between I'm not sure about! Do they have similar charge, alternating in sign, or simply zero charge? If it is...

Consider a thin parallel plate capacitor of an area of of 2.0x10^-4 metres squared, with a thickness of 1.2x10^-4 metres. The top and bottom thirds of the capacitor are filled with a dielectric material with a relative dielectric permittivity εr1=4, and the central third, with another material...