# What is a volt ?

1. Jul 6, 2004

### bayan

what is a "volt"?

hi to all friends.

what is a "volt"?

can you pl explain the meaning of that word and also "watt" (i know it is used to mesuare the amount of energy but that is about all)

2. Jul 6, 2004

### chroot

Staff Emeritus
There are many ways to define a volt:

A volt is the potential difference that will cause 1 ampere of current to flow through a 1 ohm resistance.

A volt is the potential difference across a conducting material which 1 ampere of current dissipates 1 watt of power.

The potential 1.43 nanometers from a proton is 1 volt.

- Warren

3. Jul 6, 2004

### chroot

Staff Emeritus
A watt is a power dissipation of one joule per second. It's also one volt-ampere.

- Warren

4. Jul 6, 2004

### JohnDubYa

A volt is a measure of potential between two points. A one-coulomb charge will undergo a net change of one joule of energy if it moves from one point to the other.

5. Jul 6, 2004

### bayan

i now understan watt but not volt really.

can you please put it in more simple way. i don't really understand what an ampeer is.

6. Jul 6, 2004

### chroot

Staff Emeritus
Every electron carries a specific charge. A coulomb of charge is the total amount of charge carried by $6.25 \cdot 10^{18}$ electrons. An ampere is this number of electrons flowing past a given point in a wire every second.

- Warren

7. Jul 6, 2004

### bayan

so! ampere is like bandwidth

and

volt is the amount of energy!

8. Jul 6, 2004

### Staff: Mentor

No. Volts are an electrical force and coulombs are like mass. So, similar to Newtonian physics, power is force times distance per unit time - or volts times amps. Energy is power (volts times amps) times time.

9. Jul 7, 2004

### JohnDubYa

No, volts are not forces.

What exactly is hard to understand using the definition I posted? Seems clear to me. I hope it's clear to most everyone else.

10. Jul 7, 2004

### robphy

I believe the correct analogy is that "charge [displaced]" (measured in Coulombs) is analogous to a [generalized]-displacement... not mass.
Then, "voltage" [akin to an electromotive-force] (measured in Joules/Coulomb) is analogous to a generalized-force, in the Lagrangian spirit. "Current" is analogous to a generalized-velocity. By the way, "Inductance" is analogous to mass.

For the beginning student, this is certainly too advanced to be properly appreciated unless the analogies are carefully presented in an appropriate example.

11. Jul 7, 2004

### bayan

im in year 11 and no background in Electricity what so ever. so can you plaese explain from start?

12. Jul 11, 2004

### bayan

Does this mean that 1 ampere will allow $6.25 \cdot 10^{18}$ electronsto pass in a second at any given point?

if that is the case will a 2 ampere wire alow twice $6.25 \cdot 10^{18}$ electronsto pass in a second at any given point ($12.5\cdot 10^{36}$)

Last edited by a moderator: Jul 11, 2004
13. Jul 11, 2004

### chroot

Staff Emeritus
Yes, bayan, that's correct. A current of one ampere is defined as 6.25 * 1018 electrons per second passing a given point in the wire.

I should note that there is no such thing as a "2 ampere wire" -- wires will carry however much current is dictated by the potential applied across them and their inherent resistivity -- at least until they melt.

- Warren

14. Jul 12, 2004

### bayan

i have another question.

1 ohm resistance is potential difference of one "VOLT" produces a current of one "ampere".

does this mean that a 8 ohm resistance is the potential diffrence of 8 "VOLTs" produces a current of one "ampere".

or

does it mean that a 8 ohm resistance is the potential diffrence of 8 "VOLTs" produces a current of 8 "ampere". (although i think this is wrong)

15. Jul 12, 2004

Staff Emeritus
The formula is Ohm's law, E = IR, where E is in volts, I is in amperes and R is in ohms. So you can work out the answers to your questions from that.

16. Jul 12, 2004

### krab

Looks to me like you do not understand exponential notation. twice $6.25 \cdot 10^{18}$ is $12.5\cdot 10^{18}$, not $12.5\cdot 10^{36}$.
This is vital, so study it first.

17. Jul 13, 2004

### bayan

thanx to all how answered. i think that i understand it now

18. Jul 13, 2004

### Janus

Staff Emeritus
One stipulation: a watt equals a volt-ampere in DC circuits or purely resistive AC circuits, but not in AC circuits in which the load is at least partially reactive (contains inductors or capacitors.

In the last case, the volt-ampere is a measure of "apparent power". To get "true" power (watts) you have to multiply the apparent power by the 'power factor' which is equal to the cosine of the angle of the phase shift between voltage and current due to the impedance (the combined effect of resistance and reactance) of the circuit.

19. Jul 13, 2004

### chroot

Staff Emeritus
Yes, yes, Janus, but you need to crawl before you can compete in triathlons.

- Warren

20. Jul 13, 2004

### DL

And, on that note, I'd like to ask a question I've been wondering about for a while.

In my grade 9 Science class, the textbook/teacher explained that a "volt" was a measure of how much power each electron was carrying. So a 9-volt battery simply meant that each individual electron coming out of that battery would have 9 "volts" of energy.

I'd been reading quite a bit ahead of myself in physics, and noticed that a unit being tossed around a lot was the "electron volt." So I asked my father, who has a Ph.D in Chemistry, what the difference was between an electron volt and a volt.

He said that an electron volt was the amount of energy each individual electron carried in a current, while a volt was a measure of the total amount of energy in a current. So my school textbook claims that a volt is a measure of energy per electron, and my father claims that a volt is a measure of total energy (adding all the electrons together).

So who's correct? My father is pretty out of the loop as far as chemistry goes, so he could well be wrong, but I wouldn't expect him to be on a seemingly basic issue like this.