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: Electric potential of a rod

  1. Aug 5, 2012 #1
    1. The problem statement, all variables and given/known data

    Here's the problem:


    2. Relevant equations

    V = ke ∫ dq/r
    V is the electric potential, ke Coulomb's constant, q the charge and d the distance.

    λ = q / L , where λ is the charge density, q the charge and L the length of the rod.

    3. The attempt at a solution

    I have one solution for the problem. What I want to know is why is my answer incorrect.
    Since electric potential is a scalar and not a potential what I calculated was the electric potential produced by the left part of the rod, from 0 to L/2, and multiplied the resulted for two due to the symmetry of the problem (I thought that the electric potential produced by the rod from L/2 to L was the same as from 0 to L/2)

    q = λ*L ⇔ dq = λ*dx ⇔ dq = α*x*dx

    V = 2*ke*α ∫0L/2 x/sqrt(x²+b²) dx

    I solved the integral and got:

    V = 2*α*ke*[ sqrt( (L/2)² + b² ) - b ]

    It is incorrect tho.
    Any help will be appreciated!
    Thanks in advance.
  2. jcsd
  3. Aug 5, 2012 #2


    User Avatar
    Homework Helper

    Read the problem text: λ=αx, the left end of the rod is at x=0. There is no symmetry.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook