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May 6th, 2004, 06:35 AM
#1
Thread Starter
Fanatic Member
What's e?
I've seen it before, I was even supposed to learn it last year, but no one has ever explained it well to me. My teacher last year was  so... I guess you guys are my only hope.
Also, coud anyone explain why E = qV (electric potential = charge * voltage, sorry if I put the terms wrong as I learned this in french). I get the fact that voltage is J/C and electric potential is J (that's how I do the problems) but I need to.. see it.
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May 6th, 2004, 07:47 AM
#2
Fanatic Member
e is just a constant, just like pi. pi, as you know, is the ratio of the circumference of the circle to the diameter.
all about e: http://mathworld.wolfram.com/e.html
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May 6th, 2004, 02:01 PM
#3
Thread Starter
Fanatic Member
Thanks.. I knew it was a constant, but the link is extremely helpful.
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May 9th, 2004, 07:53 AM
#4
Fanatic Member
Think of voltage as potential per unit charge. i.e. it requries 1J of energy to move 1C of charge through a potential difference of 1V.
If you think of voltage like that, it follows naturally that potential energy change is the amount of charge multiplied by the voltage difference between two points.
I'd use U for the potential energy, too, because E is generally taken to be the electric field vector.
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May 9th, 2004, 08:49 AM
#5
Thread Starter
Fanatic Member
The quiz on this electric stuff was extremely fun, lol. Everyone brought their page with all the formulas except me.. I knew them all until the last problem.
It was.. You had a battery with voltage X, hooked into ... umm.. two big plates that had the current passing between them (?) and your electric field (N/C) was Y and I had to find the distance between the two plates.
I almost paniced, but just broke both down into their basics:
V = J/C = m^2/s^2*kg/C
N/C = m/s^2*kg/C
everything cancels itself out except m.
V/(N/C) = m
Voltage/Field = distance.
Score. Just goes to show you don't even need to know the formulas to start with .
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May 9th, 2004, 09:38 AM
#6
Fanatic Member
yep, you used dimensional analysis bear in mind it won't always work, e.g. if the equation you wanted had a dimensionless constant (like 2) in it.
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May 9th, 2004, 12:45 PM
#7
Thread Starter
Fanatic Member
That's true, I forgot that:
V has the electric constant in it (you know, 9.0*10^9)... but so does N/C.
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May 9th, 2004, 01:15 PM
#8
transcendental analytic
thats the permeability constant, and is annotated epislon and not e, which is the elementary charge
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