Does the Potential Energy Increase or Decrease in Quantum Theory Problem 5?

[R.Harmon]

"5. Indicate whether the potential energy of the system increases (i) or decreases (d) in each of the following:
a) two electrons move away from one another

b) an electron is moved toward a proton

c) two protons move away from one another

d) a Na1+ ion moves toward a Cl1- ion

Use the first letter (i or d) separated by a comma but no space.

For example, use d,d,i,i to indicate that the potential energy decreases in the first two, but increases in the last two."

Intuition would tell me that the answers decrease, increase, decrease, increase, but aparently that's wrong, and I have no idea how to go about this problem. Any help? Thanks in advance.

 

[dextercioby]

Okay, so where is the quantum part? For each point you need to know the expression for the electrostatic interaction energy for two pointlike charges.

Daniel.

 

[R.Harmon]

Okay, so where is the quantum part? For each point you need to know the expression for the electrostatic interaction energy for two pointlike charges.

Daniel.

It's in a set of questions called "quantum theory". As for the electrostatic interaction energy for two pointlike charge, I have no idea what that means. Not sure this should be in this section or not, I'm not American so I don't know how the college system works.

 

[dextercioby]

U know that

$$\vec{F}_{Coulomb}=-\nabla U$$

, so, by knowing the expression for the Coulomb force, you can find the electrostatic energy.

Daniel.