# Homework Help: Equopotential help

1. Feb 23, 2012

### sasuke07

1. The problem statement, all variables and given/known data
1.Rank the electric potential at the four points A, B, C, and D from greatest to least?
2.The E Field at C points which way?
3.The force on a -4 nC charge placed at A is in what direction?

2. Relevant equations
no equations needed.

3. The attempt at a solution
1. when i was ranking their strength i thought the farther they were the stronger they were. But now i am thinking the closer they are to the charges the stronger they will be. I think the ranking is B, A, C=D. Could someone tell me if this is right or wrong.
2. I thought that C will be pointing to the top right as its on the 15+line and positive pushes away. But that was wrong. Any suggestions?
3. I thought it would point to the bottom left because negative would be attracted to the +15 but again that was wrong. Could some help on this.

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2. Feb 23, 2012

### SammyS

Staff Emeritus
For #1:

For #2 & #3:

How is the direction of the electric field related to equi-potential lines ?

3. Feb 23, 2012

### sasuke07

1. okay, but do you think my rating is correct. strongest to weakest. as well as the general thought process.
2. No idea, i don't really know what i was thinking. Could you tell me how to figure out the direction, maybe an example. Thanks

4. Feb 23, 2012

### SammyS

Staff Emeritus
#1: No. The Electric field is stronger where the equipotential lines are closer together. This asks you to rate the Electric potential from greatest to least.

This ranking has nothing to do with the spacing of the equipotential lines.

#2: $\displaystyle V_b-V_a=-\int_a^b \ \vec{E}\cdot\vec{d\ell} \,.$ So, if $\vec{E}$ is perpendicular to $\vec{d\ell}$, what does that say about Vb - Va ?