1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Find current drawn from the cell

  1. May 16, 2014 #1


    User Avatar
    Gold Member

    1. The problem statement, all variables and given/known data
    A cylindrical conductor of length l and inner radius R1 and outer radius R2 has specific resistance ρ A cell of emf e is connected across the two lateral faces of the conductor. Find the current drawn from the cell.

    3. The attempt at a solution
    Consider a thin shell of radius dx from the centre of the cylinder.

    [itex]dR = \dfrac{\rho l}{2\pi x dx} \\

    di=\frac{e}{dR} [/itex]

    Now, if I integrate the above equation I get a different answer.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. May 16, 2014 #2


    User Avatar

    Why are you integrating? You can find the cross-sectional area of the cylinder directly.
  4. May 16, 2014 #3
    It's not very clear but I think the connections are applied to the cylindrical surfaces and not to the flat surfaces at the end. So the current will be radial rather than axial. Usually the "lateral area" of a cylinder is used to designate the area of the curved surface not of the flat bases.

    If this is NOT the case, then it is a trivial problem and you don't need to integrate.

    And what do you mean by a "different answer"? Different in respect to what?
  5. May 16, 2014 #4


    User Avatar

    I do believe you are correct.

    In that case, when setting up the integral, the OP should be careful about what is the length and what is the area (with respect to the resistivity) when setting up the integral. The equation he used is not correct.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted