How about inductors:
The engineering equation for inductors is simular th that of capacitors.
L = inductance in henri
V = voltage in volts
I = current in amperes
t = time in seconds
V = L dI/dt
which means that the current through a one henrie inductor will change at the rate of one ampere per second with a one volt drop across it.
Doug Hale
Doug Hale wrote:
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Lets look at some of the mathamatical relationships:
C = capacitance in Farads
Q = charge in Coulohms
V = voltage in Volts
I = current in amperes
t = time in seconds
C = Q/V
I = Q/t or Q = I t
substituting
C = I t/V or I = C * V/t
which is actually I = C dV/dt ( the little d sort of means the "change in" - it is actually the derivitive - which is the slope of a curve - or "change in")
which is saying that the voltage accross a one farad capacitor will change at the rate of one volt per second at one amp of current flow.
Notice that in the final equation (I = C dV/dt) we didn't worry about electric field strength or charge - just current and voltage.
So was all the other discusions worthless - not hardly - you have a better idea how a capacitor works - it is science instead of magic - I can use science - I cant use magic.
So as an engineer, to me a capacitor is I = C dV/dt. But as a scientist, it is plates, dielectrics, charges and fields.
I can design many interesting things with I=C dV/dt, but it ain't magic - its the way things are.
Doug Hale
C of a capacitor is determined by the area of the plates and the dielectric constant
Jim Purcell wrote:
Doug,
The charge IS in the plates, the field IS in the dielectric.
Cook seemed to fall short of saying that. First off, the charge
he referred to was not the resulting stored energy but that
what produced the storage in the first place.
The charge and the field ARE NOT the same thing.
An electric field exists between two opposite charges.
OK, I see that. Now, does the potential at the capacitor terminals
constitute the charge. I guess it does, I think I have always thought
of the charge as all those stored electrons. Where do they live, or
do they live at all? Maybe the charge doesn't consist of misplaced
electrons but the field. Countless years of oversimplification of a
concept. But as I said, it didn't undermine my ability to use capacitors.
Not any more than using conventional current or electron flow.
Jim
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