Equipotential Lines Homework: Calculating Electric Field Strength

[hrs90]

Homework Statement

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

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?

Homework Equations

-E=ΔV/Δs (That's what I think...)

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.

 

[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.

 

[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.

 

[Mindscrape]

Where did you get 15 from?

 

[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 I am totally confused! :/
I don't know how to read these graphs, my teacher never really talked about them.

 

[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.

 

[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. :)