# Finding the magnitude of the electrostatic force from a thin rod

## Homework Statement

The figure shows a uniformly charged thin rod of length L that has total charge Q. Find an expression for the magnitude of the electrostatic force acting on an electron positioned on the axis of the rod at a distance d from the midpoint of the rod.

http://ezto.mhecloud.mcgraw-hill.com/13252699451980596522.tp4?REQUEST=SHOWmedia&media=c21q56a.png [Broken]

## Homework Equations

F = $\frac{kQ}{d^{2}}$

## The Attempt at a Solution

I know how to find the force from a point charge using the equation above, but I am not sure how to set up this problem because it is a charged thin rod. I was thinking I could divide Q by L as the charge in the above question and d-$\frac{L}{2}$ as the d in the above equation.

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Can you tell what is the formula for the force between two point charges q1 and q2 at a distance d from each other ? The formula you have written doesnt make much sense.

Can you tell what is the formula for the force between two point charges q1 and q2 at a distance d from each other ? The formula you have written doesnt make much sense.

F = (k*q$_{1}$*q$_{2}$)/r$^{2}$

Hope this is right. I suppose q1 would be the charge of the thin rod and q2 would be the charge of the point, which is e.

F = (k*q$_{1}$*q$_{2}$)/r$^{2}$

Hope this is right.

Right

I suppose q1 would be the charge of the thin rod and q2 would be the charge of the point, which is e.

No.Coulomb's law applies only to point charges.You cannot apply this directly when a continuous object like a rod is present.We will have to consider rod as composed of infinitely many point charges.

Are you familiar with calculus ?You will need integration whenever a continuous charged body is present.