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: Rate of Change problem

  1. Sep 20, 2010 #1
    1. The problem statement, all variables and given/known data
    According to Ohm's law, the voltage V, current I, and resistance R in a current are related by the equation V = IR, where the units are . . . Assume the voltage is constant V = 12V. Calculate:
    a) The average ROC of I with respect to R for the interval from R = 8 to R = 8.1
    b) The ROC of I with respect to R when R = 8
    c) The ROC of R with respect to I when I = 1.5

    2. Relevant equations
    I'm assuming something like f(x) = lim(h->0) of f(x+h) - f(x)/h or finding the f'(x

    3. The attempt at a solution
    I'm not really even sure how to set this problem up. I have about a million problems with this homework set, have seen the teacher, have seen a tutor, nothing really seems to help.
  2. jcsd
  3. Sep 20, 2010 #2
    If someone could at least send me a link of a similar problem so I can look at it, I would appreciate it.
  4. Sep 21, 2010 #3


    Staff: Mentor

    This means that IR = 12, or I = 12/R. So here I = I(R) is a function of R.
    For the average rate of change, calculate (I(8.1) - I(8))/(8.1 - 8)
    Here you want the instantaneous rate of change -- dI/dR, evaluated at R = 8.
    Solve for R as a function of I, then take the derivative. Here you want the instantaneous rate of change -- dR/dI, evaluated at I = 1.5.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook