# Power supply voltage homework

1. Jun 30, 2006

Need a little help here....getting started. I don't really understand what to use here.

If two 1000W toasters were to be connected in series to a dc power supply, what power supply voltage would be neccessary for normal operation? Assume each toaster was designated to a 120V ac circuit.

A. 110V
B. 120V
C. 170V
D. 240V

I'm guessing it is above 120V...so C or D. Just because I know that dc power takes more voltage to get 120V to ac.

Thanks,

2. Jun 30, 2006

### chroot

Staff Emeritus
Find the resistance of the toasters, and solve for the DC voltage necessary to have each dissipate 1000W.

- Warren

3. Jun 30, 2006

Ok....so here is what I did.

2000W/240V = 25/3.......using P=IV

2000W/(25/3)^2 = 28.8Ohm......using P=I^2R

Now, using R = V/I........28.8Ohm * (25/3) = 240 V

Is that right?? If so.....then my answer would be D.

4. Jun 30, 2006

### chroot

Staff Emeritus
I agree with your answer. I would have calculated the resistance for each toaster independently, though.

Also, I strongly suggest using units more often. Intermediate answers like "25/3," without units, make your work hard for anyone to follow, including yourself.

- Warren

5. Jun 30, 2006