Change in electric potential energy

[Wes Turner]

Homework Statement

As an electron (q2) moves from point A to point B, it moves farther from a positive charge (q1). Does the electric potential energy increase, decrease, or stay the same.

Homework Equations

U=-kq1q2/r

The Attempt at a Solution

The electric potential energy decreases in magnitude and absolutely.

Since r is increasing, the magnitude of U is decreasing. Since q1 & q2 are of opposite sign, (-kq1q2/r) > 0 , so U is also getting closer to zero. If q1 & q2 had the same charge, the magnitude of U would be decreasing, but it would be getting less negative so actually increasing.

I am concerned because an answer I found online has it the other way around.

 

[TSny]

I am concerned because an answer I found online has it the other way around.

Your difficulty appears to come from the negative sign in your equation U=-kq1q2/r. Are you sure it should be there?

 

[haruspex]

U=-kq1q2/r

Where are you getting that from? What is the context for it, i.e. how is U defined there?

 

[PumpkinCougar95]

The Electric potential energy is just $$ U =~ K \frac {q_1 q_2} {r} $$ without the minus sign.

Since the force between an electron and proton is attractive, it would take work to separate the two. That work goes into the potential energy, Hence it is Increasing. But the potential energy is still negative since the electron is in a bound state. You are right about the fact that it is getting closer to zero.