1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Problem 2 (please help)

  1. Mar 15, 2007 #1
    A certain sample carries a current of 4 A when the potential difference is 2V and a current of 10 A when the potential difference is 4V. This sample:
    A) obeys Ohm law
    B) has a resistance of 0.5 ohms at 1V
    C) has a resistance of 2.5 ohms at 1V
    D) has a resistance of 2.5 ohms at 2V
    E) does not have a resistance

    my work:
    R= V/I= (2/4) = .5
    R= (4/10)= .4

    The answer according to the book the answer is B. I do not see how they got that answer could someone please explain. Thank you
     
  2. jcsd
  3. Mar 15, 2007 #2

    berkeman

    User Avatar

    Staff: Mentor

    Maybe try plotting R(I) to see if something pops out. You have two data points already -- do any of the answers A-E also fit with the other two data points?
     
  4. Mar 15, 2007 #3
    Is there a way to go about it mathematically without graphing?
     
  5. Mar 15, 2007 #4

    berkeman

    User Avatar

    Staff: Mentor

    I suppose, but even with graphing the two points (and the unknown point at 1V), it's not obvious to me how to proceed. The resistances are different at each of the points, and are not equal to the slope of the line between them. Even if the resistance is varying linearly with current, you will not get the same answer of 0.5 Ohms at both 1V and 2V. Are you sure the problem and answer are stated correctly?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?