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

1. Sep 8, 2013

### nuagerose

1. The problem statement, all variables and given/known data

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]

2. Relevant equations

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

3. 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.

Last edited by a moderator: May 6, 2017
2. Sep 8, 2013

### Tanya Sharma

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.

3. Sep 8, 2013

### nuagerose

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.

4. Sep 8, 2013

### Tanya Sharma

Right

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.

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