# Electric potential when there is a negative test charge?

1. Mar 1, 2014

### applestrudle

For when there is a negative test charge:

The work done to get from infinity to r would be negative, corresponding to a decrease in potential energy so

since dr must be a path element and therefore in the negative direction (towards the source of the E field)

does that mean the direction of the force I apply would be towards infinity?

2. Mar 1, 2014

### Staff: Mentor

I believe a negative charge experiences a force towards the direction of the source of the E-field.

3. Mar 2, 2014

### sophiecentaur

A field doesn't really have a 'source', though. A static E field exists between two charges or between a charge and infinity. It is far better just to start with the definition of field and potential (which involves energy or force associated with a Unit Positive charge) and just go along with where the signs of the charges and directions of any vectors etc. If you try to have a different rule for what will happen for every combination of charge sign, etc., then you are making life hard for you and your memory. Physics tries to avoid that sort of problem.