# Electric Point Forces in a Circle

toosha88

## Homework Statement

Twelve identical point charges are equally spaced around the circumference of a circle of radius 'R'. The circle is centered at the origin. One of the twelve charges, which happens to be on the positive axis, is now moved to the center of the circle.

Part A
Find the magnitude of the net electric force exerted on this charge.
Express your answer in terms of some or all of the variables q, R, and appropriate constants.

Part B
Find the direction of the net electric force exerted on this charge.

## The Attempt at a Solution

PART A:
- i drew the diagram of a circle with radius R and one of the 12 points at the center.
- i am fairly certain i need to use the principle of superposition but with 11 other points im not sure where to start

PART B:
- didnt attempt yet because need part A first.

Any help at all would be appreciated im so confused!

## Answers and Replies

Homework Helper
hi toosha88! hmm … with 11 equations to deal with, i'd be looking for a short-cut hint: try calculating the force as if there were still 12 charges round the circle …

then calculate the difference with only 11 toosha88
Thanks for the advice! But, if i were to calculate the force in the middle of the circle wouldn't that just equal zero?
Would i then just calculate the force on the ONE charge inside the circle?
Im still confused!! Homework Helper
hi toosha88! (just got up :zzz: …)
Thanks for the advice! But, if i were to calculate the force in the middle of the circle wouldn't that just equal zero?

Yup! Would i then just calculate the force on the ONE charge inside the circle?

(i assume you mean from the one charge outside the circle?)

yes, but you'd need to subtract it, wouldn't you? 