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: Torque on/due to dipoles.

  1. Jan 24, 2010 #1
    1. The problem statement, all variables and given/known data
    Two dipoles as in pic below a distance r apart, find the torque applied to each dipole due to the other.
    [tex]\uparrow1 ------------2\rightarrow[/tex]

    2. Relevant equations
    [tex]\itshape \vec{p}=p(cos\:\theta \hat{r}-sin\:\theta\hat{\theta})[/tex]
    [tex]\itshape \vec{E}=\frac{p}{4\pi\epsilon_{0}r^{3}}\: (2cos\:\theta\hat{r}+sin\:\theta\hat{\theta})[/tex]
    [tex]\itshape \vec{N}=\vec{p}\:X\:\vec{E}[/tex]

    3. The attempt at a solution
    well i only am concerning myself with the non constants in the cross product.
    [tex]\itshape \vec{N}=\vec{p_{2}}\:X\:\vec{E_{1}}[/tex]
    [tex]\itshape (cos\:\theta\hat{r}-sin\:\theta\hat{\theta})X(2cos\:\theta\hat{r}+sin\:\theta\hat{\theta})[/tex]
    ok this is where i am confused... do i use \theta as angle under the z axis for the direction the dipole and electric field are pointing, or do i use them for angles of separation or what? if i use them for angle under the z axis for the vector it is pertaining to i get the torque will be [tex]-3cos\:\theta sin\:\theta sin \:\phi\hat{i}+3cos\:\theta sin\:\theta cos \:\phi\hat{j}[/tex], which applying angles under z axis is 0. But that isn't what the answer should be.
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted