# Two Opposite Point Charges

## Collaborate

What would happen to a positive test charge
placed very close to the positive charge (left half of the
diagram)?
Remain Stationary

Go
out to infinity

Go
to the negative charge

What is the value of the electric potential at the midpoint of two
opposite point charges? What is the electric field at that point?

Imagine that two equal but opposite point
charges approached each other until they were almost touching.
What would this look like?

- Find the potential V at point P. P is on a perpendicular bisector to the
line connecting the two +Q charges, and is a distance z away from that line.
Note that one charge is at +Q while the other is at -Q.
- Can you find the electric field at this point using the same
method as you would for two +Q charges? If not, explain why. If
you can, calculate the field. (there is
a similar question
on a previous page).
- What is the field in the limiting case z>>d (z much larger than d)?
Can you explain this?

All done? Head over to the dipole page.

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