Electric Potential Ranking & E Field Direction: Homework Help

[sasuke07]

Homework Statement

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?

Homework Equations

no equations needed.

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.

 

[SammyS]

Homework Statement

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?

Homework Equations

no equations needed.

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.

For #1:
They're asking about the electric potential, not the electric field.

For #2 & #3:

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

 

[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

 

[SammyS]

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

#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 V_b - V_a ?

 

[asteriatic]

1. Your ranking is incorrect. The electric potential at a point is determined by the distance from the source charges and the amount of charge they possess. In this case, A and B are equidistant from the 15 nC charge, but B has a larger charge, so it will have a higher electric potential. C and D are also equidistant, but C has a larger charge, so it will have a higher electric potential. Therefore, the correct ranking is B, A, C, D.
2. The E field at C will point towards the 15 nC charge. This is because the E field always points in the direction of the force that a positive charge would experience. Since a positive charge would be repelled by the 15 nC charge, the E field points away from it.
3. The force on a -4 nC charge placed at A would be directed towards the +15 nC charge. This is because opposite charges attract each other, so the -4 nC charge would be pulled towards the +15 nC charge.