Electric Potential: Calculating Energy & Power

[alligrass]

Homework Statement

how much energy is wasted when 35 C of charge flow through a 120 V toaster in 5.0 S?
how much power?

Homework Equations

work=qv i think...

power= work /time

The Attempt at a Solution

i thought to find energy wasted i would find the work used. (?yes?)

so i guess that would be 35(120) whihc is 4200 J


so then do i power = 4200/5=840


is this correct?

 

[fubag]

well P = IV

and they give you the time...so you know the units of Power = (Joules/second), so given the time you can find the joules wasted...

both problems solved with one equation!

:D

 

[alligrass]

wait i didnt really understand what u just said.
did i do this right or is it wrong?

 

[fubag]

no recheck your work and look at the formula I gave you and the units of power, energy is in JOULES, and power is in Watts or Joules/second...it should be straightforward from there

 

[alligrass]

well a watt = J/sec
so i got energy in joules correct right??

then those Joules per 5 sec gives u 840 J/ a sec

 

[fubag]

ok another formula that will help is to know that I (current) is equal to (change in Q- the charge)/ (change in time - seconds), both of these informations are given in the problem...

once you find I...you can solve for P = IV, using the information given in the problem...

 

[fubag]

oh and I forget to mention that the change in potential difference (V) is equal to the potential-energy change per unit charge in moving across the toaster...so U = Vq...you know volts and know q so you can find the energy lost.

 

[alligrass]

so isn't i=7
and then 7(120)=840...

 

[alligrass]

ddint i do that in the proble, above?

 

[fubag]

ohh..lol my bad, yes your work is correct, sorry for the explanation again above...wasn't thinking so simply...