# Homework Help: Trying to find electric field

1. Feb 18, 2013

### Triathlete

The Problem:
The electric potential in a certain region is
V = αx2y2+βz2(x2-γ)+δy3z
where α = 5 V/m4, β = 4.5 V/m4, γ =6.8 m2, and δ = 7.1 V/m4.
What is the y component of the electric ﬁeld Ey at (1.3 m, −3 m, 4.4 m)?

My Attempt:

I took the partial derivative with respect to y and got
Ey = 10x2y + 4.5z2(x2-6.8) + 21.3y2z

(But I think I may have done that wrong....)

I then plugged in my values for x, y, and z, and got 347.5968 as my answer, which was wrong. Any help would be appreciated! :)

2. Feb 18, 2013

### TSny

Can you show how you got your middle term with the factor of 4.5? The middle term of V doesn't seem to depend on y.

Also, the components of E are not given by the partial derivatives of V (but close!)

3. Feb 18, 2013

### Triathlete

Thanks for the response,
I knew I must have messed something up in that derivative. So it should be Ey = 10x2y+21.3y2z.

But if not the partial derivatives, then I am confused as to what I am supposed to be looking for.

4. Feb 18, 2013

### TSny

See here and note if there's something you left out.

5. Feb 18, 2013

### Triathlete

Ooooh I see. Got it! Thanks so much!