# Electric dipole

1. Jan 23, 2009

### jan2905

An electric dipole consists of a pair of point charges each of magnitude 4nC seperated by a distance of 6cm. What is the electric field strength at the point midway between the charges?

Not sure what equations to use?

Any ideas?

2. Jan 23, 2009

### AEM

I'll get you started: Draw a picture of your two charges. Sketch in the electric field for each, notice you have an electric field vector coming out from the positive charge (due to the + charge) and an electric field going in to the negative charge (due to the - charge). That means you'll have to add those two fields together eventually.

Now, you need an equation that relates electric field, E, charge, q, and distance from the charge, r. There's one that does it. (Oh, it will have a proportionality constant, too.)
You'll need to figure out the distance you want to use and plug in numbers.

3. Jan 24, 2009

### jan2905

yeah, but it is only for one charge... so, would you figure out the E for Q, then the E for q... both at 3 cm... then "add them?"

4. Jan 24, 2009

### chrisk

There are two charges, +Q and -Q, that form an electric dipole. Use the principle of superposition. Calculate the E field created by +Q at r = 0.03 m, keeping in mind the direction of the field, and likewise with -Q. Add these two vector values and this will give you the desired result.