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Homework Help: A simple diagram of two heat resistors.

  1. Mar 25, 2009 #1
    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. jcsd
  3. Mar 25, 2009 #2


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    Welcome to PF!

    Hi KayVee! Welcome to PF! :smile:

    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?
  4. Mar 25, 2009 #3
    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: [tex]P = W / t = 2112kJ / 1200s = 1,76 kW.[/tex]

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

    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.
  5. Mar 26, 2009 #4


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    Hi KayVee! :smile:

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

    (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 :wink:)

    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 :wink:)
    Noooo :frown:

    you need another equation for R1 and R2 … try the other diagram! :smile:
  6. Apr 5, 2009 #5
    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: [tex]U=I*R[/tex].

    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 : [tex](R1 * R2)/(R1 + R2)= Rtotal[/tex].
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