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!

Einstein Notation - Not sure if my answers are right

  1. Feb 15, 2013 #1
    1. The problem statement, all variables and given/known data

    Questions 11 and 12 specifically..
    29dzc43.png

    2. Relevant equations



    3. The attempt at a solution
    11(a)
    e7ze36.png

    11(b)
    2hhkp35.png

    12(a)
    2rhrxp1.png

    12(b)
    34pgaad.png
    oky1lf.png

    12(c)
    2vdi8o7.png
    mslys6.png

    12(d)
    35k4wme.png
    ru9svs.png

    (I did the last part of 12(d) by normal vector methods and got 2a instead...which is the correct answer)
     
    Last edited: Feb 15, 2013
  2. jcsd
  3. Feb 16, 2013 #2

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    An index shouldn't appear more than twice. For the first one, for example, you should have
    $$\frac{\partial}{\partial r_i} (r_j r_j)^{n/2}$$
     
  4. Feb 16, 2013 #3
    Thanks for your reply!

    Also, I can't see what's wrong with my final answer in part 12(d)...i think the last line is the cross product of ∂j and r which equates to zero??

    I think I have figured out every question other than part 12(d)
     
    Last edited: Feb 16, 2013
  5. Feb 16, 2013 #4

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Hint: ##\partial_i r_j = \delta_{ij}##. You can use that in several of the problems. In 12b, you need to use the product rule.
     
  6. Feb 16, 2013 #5
    thanks i think i've sorted it out!
     
  7. Feb 16, 2013 #6

    WannabeNewton

    User Avatar
    Science Advisor

    It is not a summation. It is just the statement that the partial of the jth coordinate function with respect to the ith coordinate function is just the kronecker delta.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Einstein Notation - Not sure if my answers are right
Loading...