Need help with Gradient in Polar Coordinates

[leonne]

Homework Statement

Well the problem is a electromagnetism problem: I need to find the charge density. Given
E= kr^3 r^

Homework Equations

formula is gradient E=p/e0

The Attempt at a Solution

They got the gradient of E to be 1/r^2 (d/dr) (r^2 Er) i have no idea how they did it i know gradient is d/dx+ d/dy+d/dz so idk how they got that from E

then they got Eo(1/r^2 (d/dr)(r^2(kr^3) ... answer p=5kEor^2

Is that just a formula for any spherical polar coordinate? 1/r^2 (d/dr) (r^2 Er) Professor said something about looking in the back of the front cover for this. I just have pdf of book and doesn't have back cover. So if it is a formula can you tell me the whole thing thanks

 

[gabbagabbahey]

First, ook up the difference between "gradient" and "divergence" ...Then look up "divergence in spherical coordinates".