Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Increment value of equvalent resistance when the resistances are parallel

  1. Jun 12, 2007 #1
    R1 & R2 are two resistances in parallel. d(R1) & d(R2) are the incremnet in resistance. If R3 is the equvalent resisitance such that R3=R1*R2/R1+R2, then if d(R3) is increment in equvalent resistance. What is the value of d(R3)/R3.
     
  2. jcsd
  3. Jun 12, 2007 #2
    Hmm, well, if this is anything like I'm seeing it to be, you're dealing with functions:
    [tex]R_3:\mathbb{R}^2\to\mathbb{R}[/tex]
    So the total differential/change of [tex]R_3[/tex] would be:
    [tex] dR_3=\frac{\partial R_3}{\partial R_1} dR_1 + \frac{\partial R_3}{\partial R_2} dR_2[/tex]
     
  4. Jun 13, 2007 #3
    Actually I found it in some place as follows

    d(R3)/R3= d(R1)/R1+d(R2)/R2+d(R1+R2)/(R1+R2), please let me know how it is arrived.
     
    Last edited: Jun 13, 2007
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook