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!

Electric potential of a dipole moment

  1. Mar 10, 2013 #1
    1. The problem statement, all variables and given/known data
    The dipole moment of a water molecule is 6.29E-30Cm. What is the electric potential's magnitude 1.43nm from a water molecule along the axis of the dipole?


    2. Relevant equations
    p = qr


    3. The attempt at a solution
    I don't have values for q or r. I just know the magnitude of the dipole moment and the distance away from the molecule in which I have to figure out the electric potential. I don't know where to go from here.

    And even if given q, how would I figure out V.
     
  2. jcsd
  3. Mar 10, 2013 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Find the electric potential of two equal and opposite charges d distance apart symbolically, at distance x from the centre of the dipole, and then take into account that x>>d.

    ehild
     
  4. Mar 10, 2013 #3
    That doesn't really help me.
     
  5. Mar 10, 2013 #4

    ehild

    User Avatar
    Homework Helper
    Gold Member

    You know the formula for the potential of a point charge? A point charge q is at x1=d/2, and an other one is at x2=-d/2. What is the potential at the point with coordinate x?

    ehild
     
  6. Oct 30, 2017 #5
    Has anyone figured out how to do this question? I have it too but I can't find the procedure anywhere online for it.
     
  7. Oct 30, 2017 #6

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Do you know what is the electric potential of a point charge at distance D from it?
    You have two charges, arranged along the x axis, both at distance d/2 from the origin. What are their potential at the point P, distance x from the origin? upload_2017-10-31_5-39-15.png
     
  8. Oct 30, 2017 #7
    How do I determine what d/2 is?
     
  9. Oct 31, 2017 #8

    ehild

    User Avatar
    Homework Helper
    Gold Member

    You do not need to determine it. The dipole momentum is given, and P=qd. At the end, you will find that the potential is proportional to qd, that is, the dipole moment.
     
  10. Oct 31, 2017 #9
    So I have P/(2q)=d/2 so far. I have also made the equations V=qk/(r-d/2) and V=qk/(r+d/2) and r is the distance from the origin to the point at which potential is measured.

    What is next? I don't understand how to substitute them since d/2, V, and q are unknown.
     
  11. Oct 31, 2017 #10
    Nevermind. I have found that the equation V=kp/r^2 works, although I don't know how this equation was derived.
     
  12. Oct 31, 2017 #11

    ehild

    User Avatar
    Homework Helper
    Gold Member

    The two charges have opposite signs. The positive charge causes V+=qk/(r-d/2) potential at distance r from the origin, and the negative charge contributes to the potential by V-=qk/(r+d/2). The potential at P is the sum of V+ and V-: ##V(r)=qk\left(\frac{1}{r-d/2}-\frac{1}{r+d/2}\right)##. Bring the fractions to common denominator and use that d/r << 1.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Electric potential of a dipole moment
Loading...