Question

When can we say that potential energy of an atom decrese or increase?when the separation increase and decrease.

Answer 1

may increase or decrease

The electric potential energy, E, between the two charges, q₁ and q₂, separated by the distance, r, is given as
E=kq1q2/r,where k=constant
As the distance between the charges is increased, the energy will decrease if both the charges are of similar nature. But if the charges are oppositely charged, the energy will become less negative and, hence, will increase.

Or

Potential energy between two charges:

(A)=k×q1×q2/r

Now if r increases and q1 andq22are of same sign then;

A be decrease.

Else if q1 and q2 are of opposite signs:

Then A be increase.

So, when the separation between the two charges is increased the electric potential energy of charges may be increased or decreased.