# definition: voltage, current

Discussion in 'Electronic Basics' started by Paul Mars, Feb 14, 2005.

1. ### Paul MarsGuest

I was trying to explain to a friend what they are and what the difference
is. My schooling in Electronics was so long ago. I feel that I still have a
very good grasp of what they are, but I could not explain them.

My friend looked them up and got this:

current (as in "electrical phenomenon") n. : a flow of electricity through a
conductor; "the current was measured in amperes"
voltage (as in "electrical phenomenon") n. : the rate at which energy is
drawn from a source that produces a flow of electricity in a circuit;
expressed in volts

p

2. ### John FieldsGuest

---
We define current to be the number of electron equivalent charges
moving past a fixed point in a specified interval of time, and we have
named the unit of charge transfer the ampere, one ampere being equal
to 6.24E18 electron equivalent charges moving past an arbitrary
reference point in one second.

We define voltage to be the force required to cause charge to move
through/against a resistance, with one volt of force being defined as
that force necessary to make 6.24E18 electron equivalent charges pass
through a resistance of one ohm in one second.

Since, then, a resistance of two ohms would require twice the force to
cause a flow of charge equal to one ampere to occur, we can write:

E 2V
I = --- = ---- = 1A
R 2R

where I is the current, E is the voltage and R is the resistance.

There's still a lot left to consider, the coulomb and the joule for
example. Do you want to go on?

3. ### Paul MarsGuest

BTW Your definition is more logical then what I learned. If you would like
please comment on voltage being defined as the potential difference between
two points period.

4. ### RatchGuest

Charge exists in two flavors, positive and negative. When it moves, as
the negative electrons in a wire, or positive or negative ions in
electrochemistry, it is called a current. It takes energy to move charges
from on place to another. The amount of energy per unit charge is voltage.
If it takes 5 joules of energy to bring 1 coulomb of charge from point A to
point B, then the voltage of point B with respect to point A will be -5
volts. Think of voltage as the amount of energy per unit charge, not force.
Voltage does produce a electrostatic field which repels or attracts a unit
charge with a finite force, but voltage by itself is not force. Wattage is
simply energy transferred per unit of time. Any good electrical text will
describe what I wrote in more detail. Ratch

5. ### Kevin AylwardGuest

Yes!

I was going to quibble with force on this one, but you done the job fine
Ratch Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

6. ### GenomeGuest

Indeedy, sort of. The Ampere was/is defined as 1 Coulombe per second of
charge passing by.

It has something to do with electrochemistry and deposition of a Molseworth

mole junior ask brane, 'if you are so clev wot is one plus one?' at which
point brane larf so much it burst into a trillion pieces.

The charge on an electeron is 1.6019dribblydribblyE-19 Coulombes. Multiply
that by Johns number of electerons and you get 1...ish.

The charge on an electeron was worked out by Millikan (sp)

Blame the Chemists.

DNA

8. ### GenomeGuest

No......! I shit you not.

The bloke was an American.

He went and suspended droplets of something that he charged up in an
electric field (no pun intended) and measured something versus something
like gravity or another thing (how fast it went up and down) and it was dead
sensitive and they all came out to be multiples of the charge on an
electeron and he found the smallest one was 1.6-19C or something.

It was a classic experiment.

DNA

9. ### John FieldsGuest

---
Milli = 1 times ten to the minus three so Millikan, with a name like
that, should have only been able to measure to one part in a thousand.

However, his exquisite experiment yielded results sixteen orders of
magnitude greater than one part in 1000, so if his surname would have
been Attodecikan, it would have fit his accomplishment. 11. ### BobGGuest

Has the OP given his friend the hydralogical analogy yet? Volts is PSI
in the hose and Amps is gallons per minute, the size of the hose is the
resistance of the wire. Seems intuitive.

12. ### GenomeGuest

Thanks for explanation.

No offence meant to you or owners thereoff.

DNA

13. ### GenomeGuest

Monster,

"Millikan first let them fall until they reached terminal velocity. Using
the microscope, he measured their terminal velocity, and by use of a
formula, calculated the mass of each oil drop."

But..... I think that's wrong.

DNA

This last election, I heard that the electerons were charging
five bucks a vote!

15. ### Rich GriseGuest

Voltage is defined as the potential difference between two points. The
"period" is a punctuation mark.

Potential is like pressure.

When you compress a spring, you give it potential energy, which it
stores up in the form of the stress on the spring itself. When you
release the spring, that energy is released as "kinetic energy", but
that's another topic.

The point is, that "potential" corresponds to "pressure." It's
something like water flowing downhill, where the "potential energy" is
represented by the height of the water column - actually, the height is
the voltage - the current, obviously, is the flow, and the power is
the pressure times the flow.

Now, if you just let the water fall, then the analogy to an electronic
circuit kind of breaks down, except that a waterfall might be kind of
conceptually like an arc.

But if it falls through a waterwheel, then you can extract energy from
it. The amount of energy you can extract at any given moment can be
expressed as (or derived from?) the flow rate multiplied by the pressure
difference. No, wait - rate - that's the rate at which you're extracting
energy. Energy and work are almost interchangeable - I had a physics
teacher who said, "Energy is the capacity to do work." Work, of course, is
force times distance. And power is the rate of doing work.

Hope This Helps!
Rich

16. ### RatchGuest

No it is not defined that way. It is often confusingly described that
way. Potiential of what?
In what way? Force per unit area vs energy per coulomb!?
No potential energy is converted into kinetic energy unless you propel
something like a pinball. It could just as easily be converted into heat by
connecting it to a dashpot.
Does the above description help anyone to really understand what
voltage is? Ratch

17. ### Fred AbseGuest

Stephen Leacock?  