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what's the deal? | |
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desolderthis 2 Posts |
Some things really test my faith in math |
Replies to what's the deal?
order matters - | |
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Gary Society of Physics... 293 Posts |
I guess the first thing I would say is that you have to be careful about the order in which you do things...for example d/dx(x^3) = 3x^2 and that is not the same as Adjunct Professor of Physics, Editor of The Physics Teacher, and GWU SPS Chapter Advisor |
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Damian Cypress 1 Posts |
First off...you have to recall that phi(r).You have to use the chain rule to properly differentiate the second guy. The answer is 2/r*d(phi)/dr+d2(phi)/dr2. The first guy just gives you the second term of the second guy. phew...did that make sense? Be careful about spherical coordinates, there's a nasty singularity at the origin. For a rigorous discussion of this topic check out Electrodynamics by Griffin, an excellent upper div text on the subject. |
Re: what's the deal? - | ||
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Dave San Marcos, Texas 441 Posts |
The difference is that in the second case, you are taking the partial derivative of a product, and so must use the product rule. This gives you two terms instead of the single term that results from the first expression. Try not to become a man of success, but rather try to become a man of value -- Albert Einstein |