Power supply voltage homework

[Bradracer18]

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 necessary 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,
Brad

 

[chroot]

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

- Warren

 

[Bradracer18]

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.

 

[chroot]

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

 

[Bradracer18]

Warren...I do use units a lot, but am unfamilar with these electric units...I didn't know what my units were on the 25/3...was it still ohms?

 

[chroot]

Power / voltage = current (in amperes). Ohm's law, which you quoted as "P = IV," has power in watts, potential difference in volts, and current in amperes.

- Warren