# About the electric field of a dipole

1. Jul 12, 2010

### norap

I would like to know that 1) Is there a point where the electric field is zero from a dipole?
2) If the point is very far away from a dipole, how is the electric
from the dipole? I mean, for example, if there is a charge +3 and
-1, these two charges will behave like a +2 point charges at large
distance.

2. Jul 12, 2010

### kuruman

Hi norap and welcome to PF.
Other than infinity, no. Just think about it. A dipole is two charges of equal size but opposite sign. If there is a point where the E-fied is zero, it should be on the line joining the charges. Any such point is going to be closer to one or the other charge. At the midpoint the electric fields from the individual charges add, they don't give zero.
2) If the point is very far away from a dipole, how is the electric
from the dipole? I mean, for example, if there is a charge +3 and
-1, these two charges will behave like a +2 point charges at large
distance.
[/QUOTE]
What you have described is not a dipole because the sizes of the charges are not the same, but yes, at very large distances this distribution will be like a +2 point charge at the origin.

3. Jul 13, 2010

### norap

Thank you very much, Karuman.

4. Jul 13, 2010

### norap

sorry, i mean kuruman. =)

5. Jul 13, 2010

### kuruman

No offense taken. People mangle my real name too, all the time.

6. Aug 9, 2010

### amaresh92

whats is use of dipole moment?