question about power

[foofighter]

i just started studying physics in Conceptual Physics, which is proving to be a good first book. I don't understand something though. It says power=voltage X current. But Current = Volts/Ohms - does that mean power = volts squared / ohms? i'm a little confused...thanks in advance for your help = )

[CPL.Luke]

you could express power in those terms, however the basic definition of power is the rate at which work is done, hence the SI unit of power is joule/sec or watt.

 

now consider that a joule is a coulomb volt so you could easily replace the volt in your equation with joule/coulomb

 

now an ohm is a volt-sec/coulomb or a joule-sec/coulomb^2 so essentially your equation says that a watt is a

 

 

joule/sec just like we would expect.

 

 

If you weren't looking for the units than I apologize and your algebra is correct v^2/R=p

[Megabrain]

Foofighter you are correct, yes you can mash those formula around v^2/r is power just as I^2 *r is also power.

[thedarkshade]

When we dealt with this at school we did it this way.

 

The work of electricity is:

[math]A=IUt[/math] the unit turn out fine too because Ampere*Volt*sec gives joule!

 

And as we all know the formula for power is:

 

[math]P=\frac{A}{t}={IUt}{t}[/math] we cancel t and get:

 

[math]P=UI[/math] so in this case it is the product of tension and intensity!

 

And you very easily proof the unit.

 

[math]P(=)IU=A\times V[/math] as [math]1A=\frac{1C}{1s}[/math] and [math]1V=\frac{1J}{C}[/math]

 

so you'd get:

 

[math]P(=)\frac{C}{s}\frac{J}{C}[/math] cancel Cs and finally

 

[math]P(=)\frac{J}{s}=W[/math]

 

Cheers,

Shade