Equipotential Lines

1. Sep 14, 2010

hrs90

1. The problem statement, all variables and given/known data
The figure below shows the equipotential lines for a uniformly varying electric field.
[PLAIN]https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/Phys1202/fall/homework/Ch-20-Potential/equipotential_lines/equ-lines-1.jpg [Broken]

A) What is the approximate strength of the electric field at point A?
B) What is the approximate strength of the electric field at point B?
2. Relevant equations
-E=ΔV/Δs (That's what I think...)

3. The attempt at a solution
I think I have to start off by dividing the voltage by the distance, but besides that I really have no idea on how to start the problem. I'm not just looking for an answer, but if anyone could get me started off I'd appreciate it.

Last edited by a moderator: May 4, 2017
2. Sep 14, 2010

Mindscrape

That's exactly what you do, divide the voltage by the distance. For the equipotential of A you seem to go approximately 10 Volts lower for every 2cm of y.

3. Sep 14, 2010

hrs90

Ok, so would it be 15 divided by 3.50 or 15 divided by 5.70? I tried both these numbers, both turn out to be wrong answers.

4. Sep 14, 2010

Mindscrape

Where did you get 15 from?

5. Sep 14, 2010

hrs90

Point A is located between 10 V and 20 V and it is kinda in the middle. So i tought it would be 15, but now Im totally confused!! :/
I don't know how to read these graphs, my teacher never really talked about them.

6. Sep 14, 2010

Mindscrape

Oh, yeah, you're just interpreting the graphs wrong. Lines of equipotential show that there would be no work to move a particle along one of the lines. So you can see from these graphs that the lines of equipotential is flat along the x axis, so there's no change ever. Ignore the x. Now, in the y axis we do get change, and that change varies, so there must be an electric field in the direction of y.

E=-∆V/∆s
so approximate the first point A by looking at the change along the y direction for that region
E=-(10-20)/(4.2-2.2)=5

I'll let you do point B.

Last edited: Sep 15, 2010
7. Sep 14, 2010

hrs90

Thank you so much man. Now not only I know how to do read the graph, I can do the rest of the homework. :)