# Homework Help: Equipotential Contours and Point Charge

1. Jan 24, 2005

We haven't really covered this in class so I need some help.

Assuming that these contours are those of a point charge at the origin, calculate the value of the charge in C.

I tried using the equation kQ/R but that's wrong, I'm not even sure I'm using it right in fact. Any help? Thanks

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2. Jan 24, 2005

### vincentchan

3. Jan 24, 2005

My calculator is just fine thanks, but i'm still getting it wrong. I'm using -7500 V as Q and then figuring out the radius by using the pythagoream theaorem, still getting it wrong. Help

4. Jan 24, 2005

### learningphysics

Why are you using pythagorean theorem? Each contour is a circle... you can measure R right off the graph... You can use any contour, but I'd use the one at R=1m.

5. Jan 24, 2005

Well both the x and y axis measure distance so i thought i'd have to find the radius of the circle by using the pythagoream theorem. Even by using r=1m i still get it wrong.

6. Jan 24, 2005

### vincentchan

write your number out and let us check for you...
warning: what is the sign of charge?

7. Jan 24, 2005