Energy functions help./

1. Dec 6, 2006

O.J.

OK, they're throwing pretty weird concepts to our heads in this PHY101 course. stuff like even partial derivatives that we didnt take in math. differentiating partially with respect to a single variable treating others as contants is NOT getting through my head. can someon PLEASE illustrate it for me?????

2. Apr 20, 2007

gammamcc

partial derive of xyz with respect to y (say) is as if z and x are just numbers
so you get xz*1= xz.

Say you replaced every other variable with a fixed number except the var. you differentiate. It is then just regular derivatives.

Remember calc 1? What is the deriv. (w/ resp. to x) of Cx^4 .....ANS> C*4*x^3. Now, change C to another variable y,z,w ...whatever.. same math.

Hope it helps.

3. May 10, 2007

Gza

$$E_p(k_X, k_Y) = \iint E_s(x,y)e^{i(xk_X+yk_Y)}\,dx\,dy$$

Last edited: May 10, 2007
4. May 14, 2007

duke_nemmerle

heh, wish I knew what text you were using, I was looking for a phy101 that does exactly this(but that it does it without warning you before you enroll is pretty nasty)

5. May 14, 2007

theperthvan

pretty sure he doesn't get the concept but he knows how to do it.

It's like the derivative wrt x (say) along a curve where z,y are constant. Drawing a picture will make it easy straight away. Think of a solid shape. Chop it into two pieces. The rate of change along the edge is kind of doing a partial derivative.