# Basic Electric Field Question

1. Dec 14, 2008

### Arg3n

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

i Can't seem to get the right answer :

A Particular dipole consists of two charges of magnitude 6.0 x 10^-12 C. If the charges are sperated by a distance of 5.0 cm, determine the size and direction of the electric field at the midpoint between the charges.

2. Relevant equations

E= Q / [4(3.14) x (8.85 x 10^-12) x r^2 ]

3. The attempt at a solution

E= [(6.0 x 10^-12)^2] / [4(3.14) x (8.85 x 10^-12) x (0.05)^2]
= 1.29 x 10^-10

but the answer is 1.7 x 10^2 N/C
So i mut be missing something or im just doing it all wrong

2. Dec 14, 2008

### hage567

Your equation is not consistent throughout your calculation (you go from Q to Q2).

You are trying to find the electric field at the midpoint between the charges; not at the location of one charge (so the r value you are using is wrong).

You must sum up the contribution from each charge at the midpoint.

3. Dec 14, 2008

### Arg3n

Thanks for the reply but I am having trouble understanding the whole charge concept, how do we sum up the contirbution of each charge?

4. Dec 14, 2008

### hage567

Take the electric field due to a point charge equation: E = kQ/r2
This is a vector, so the total electric field at the midpoint will be Etotal = E1 + E2
It's a dipole arrangement, so one charge is negative and one charge is positive. This tells you the direction of the electric field due to that charge.

See http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elefie.html#c2