Calculating Electric Force on -3.29µC Charge at y=0.493m

[Lannie]

Hi, I am having some trouble with the following problem:

Calculate the electric force on a -3.29microC charge placed on the y-axis at y=0.493m.

First I calculated the electric field at y=0.493m using the equation

E= (1/4piEo)*(q/r^2)

and found the electric field at that point to be -1.22E-5.
Then to find the electric force, I used F=qE and found F to equal -0.401 N. But for some reason this doesn't work out to be the right answer. If anyone could tell me where I've gone wrong, it would be much appreciated.

 

[jtbell]

Hi, I am having some trouble with the following problem:

Calculate the electric force on a -3.29microC charge placed on the y-axis at y=0.493m.

If that's the complete statement of the problem, you should be having some trouble with it!

You need some information about whatever it is that is exerting an electric force on the charge in question.

First I calculated the electric field at y=0.493m using the equation

E= (1/4piEo)*(q/r^2)

That would be useful if you wanted to find the force that your given charge exerts on some other charge located 0.493m away (for example located at the origin). But even there you'd have to know how big that other charge is.

 

[wais]

Your calculations seem to be correct. The only thing I would double check is the units. The electric field is usually measured in N/C and the charge is in C, so the force should be in N, not N/C. Make sure to double check your units and see if that helps. Also, make sure you are using the correct value for the electric constant, which is 8.99E9 Nm^2/C^2. Other than that, your calculations and approach seem to be correct.