# Electric Field at center of triangle

ashkash
Three 18.0cm long rods form an equilateral triangle. Two of the rods are charged to + 13.0nC , the third to - 13.0nC .

What is the electric field strength at the center of the triangle?

I have spent a lot of time on this problem and have not been able to get anywhere. Please help.

## Answers and Replies

FluxCapacitator
Try finding the field exerted by one rod at at time, and then add it all together vectorally.

ashkash
Wouldnt two of them cancel out as they have the same charge?

FluxCapacitator
They do have the same charge, but not opposite directions. Only part of them will add together. Each rod will have it's own electric field exerted at the center point of the triangle. If you add each of those electric field vectors up, you should get the right answer, but be sure to teart them all as a vector.

ashkash
I am still having a hard time with this. What would be the formula to use for calculating the electric field, E=kq/r^2? And what would I use as r? Thanks for the help.

Homework Helper
ashkash said:
the electric field, E=kq/r^2?
This formula for electric field is due to a point charge at distance r from it, but in yout problem the charge is distributed over the rod or it is a linear charge distribution.

First find out the field due to charge on one rod by taking an infinitely small charge on a small element of the rod, have components along and perpendicular directions and then by integrating find the field due to the whole rod. Then the vector sum of the three fields will give the required field strenght.

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