Homework Help: A simple diagram of two heat resistors.

1. Mar 25, 2009

KayVee

Here is a problem I have. I need to find the resistors R1 and R2, and here is what I know:

http://triton.imageshack.us/Himg12/scaled.php?server=12&filename=varmalikam.jpg&xsize=640&ysize=480 [Broken]

How do I set up the equation? Im really lost.

Please ask, if you are having troubles reading the diagram. The first one is the original one.

Last edited by a moderator: May 4, 2017
2. Mar 25, 2009

tiny-tim

Welcome to PF!

Hi KayVee! Welcome to PF!

Ignore the first diagram.

In the second diagram, you're given the heat and the time and the voltage …

so what is the power?

and so what can you say about R1 and R2?

3. Mar 25, 2009

KayVee

I see that I need to put up my own work/study on the circuit, but now I see that I was going no where :P

So, the power for the paralell is: $$P = W / t = 2112kJ / 1200s = 1,76 kW.$$

Then the (sum of the?) paralell resistors: $$R = V~2 / P = 220~2 / 1,75 kW = 27500 kOhm.$$

Can I then say that each resistor is 27500 / 2 ?

This pice is kinda hard, since we have had so little about power in school.

4. Mar 26, 2009

tiny-tim

Hi KayVee!

(why did you use W for energy … that's really confusing )

(and the LaTeX for squared is ^2 not ~2 … though it's quicker to write, and easier to read, and easier on the PF server, if you just use the X2 tag above the Reply box )

yes, except I think it's 396 kJ for that diagram
yes (but it would be better if you stated what formula you're using )
Noooo

you need another equation for R1 and R2 … try the other diagram!

5. Apr 5, 2009

KayVee

Sorry tiny-tim, for the late reply. But I cracked the case :D I found the total ampere for
the second diagram, and then just setting the information I had in: $$U=I*R$$.

I knew that the total resistance in the serial diagram var 146,67 Ohm. There is even a simpler way to find the res. for each resistor. Find the total resistance for the paralell and and total for the serial, then set it up in the : $$(R1 * R2)/(R1 + R2)= Rtotal$$.

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