# Homework Help: Electric potential

1. Mar 5, 2008

### alligrass

1. The problem statement, all variables and given/known data

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

2. Relevant equations
work=qv i think...

power= work /time

3. 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?

2. Mar 5, 2008

### 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

3. Mar 5, 2008

### alligrass

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

4. Mar 5, 2008

### 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

5. Mar 5, 2008

### 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

6. Mar 6, 2008

### 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...

7. Mar 6, 2008

### 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.

8. Mar 6, 2008

### alligrass

so isnt i=7
and then 7(120)=840.......

9. Mar 6, 2008

### alligrass

ddint i do that in the proble, above??????

10. Mar 6, 2008

### fubag

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