# Homework Help: Potential Difference, given E

1. Nov 1, 2007

### aliaze1

1. The problem statement, all variables and given/known data

What is the potential difference between yi= -5cm and yf=5cm in the uniform electric field E = ( 20,000{ i } - 50,000 { j } )V/m?

2. Relevant equations

∆V = V(sf) - V(si) = -∫ Es ds

with the limits of the integral being sf and si

3. The attempt at a solution

I tried doing the integral, resulting in (E2)/2, and then multiplying proceding as so:

E= √ (200002 + 500002) = 53851.64807
(E2)/2 = 14500000 = x
x |0.05,-0.05 = -{x(0.05) - x(-0.05)} = -{2[x(0.05)]} = -1450000 = incorrect

any help?

thanks!

2. Nov 1, 2007

I think you're taking the integral as if it were E dE instead of ds (Compare with the case where if it were the integral of x dx, then the integral is x^2/2). E is a constant since it is "uniform", so you can treat it as a constant and pull it out of the integral. If you're only dealing with one dimension (along y), then the integral of E ds simplifies to E(Sf - Si).

3. Nov 1, 2007

### aliaze1

aaahh lol nice....yea that was my mistake...lol whenever i see the integral sign i jump to conclusions without looking at the second part

thanks!

4. Nov 2, 2007

### aliaze1

well actually...i tried that and it didn't work:

E = 53851.64807

Sf-Si = 0.05 - (-0.05) = 0.1

E * (Sf-Si) = 53851.64807 * 0.1 = 5385.164807 = Incorrect :(

Any help?

Thanks!

5. Nov 2, 2007

### aliaze1

I have only one attempt left. I noticed that I didn't put the negative sign there, but the computer would tell me to 'check your signs' if this was a sign issue...so i assume it isn't

6. Nov 3, 2007

any help?