Question 1

What is the difference between electric potential and electric potential energy?

Accepted Answer

Electric potential (V) is the work done per unit positive charge to move it from infinity to a point in an electric field. It's a property of a point in space. Electric potential energy (U) is the total work done to bring a specific charge from infinity to that point. It's a property of a charge at a point. So, $U = qV$.

Question 2

Why is electric potential at infinity considered zero?

Accepted Answer

Infinity is chosen as the reference point for zero potential because the electric field and force due to any finite charge configuration effectively become zero at an infinite distance. This makes calculations simpler and provides a consistent baseline for defining absolute potential.

Question 3

How can electric potential be negative?

Accepted Answer

Electric potential can be negative if the source charge creating the field is negative. A positive test charge would be attracted to a negative source charge, meaning the field does work *on* the test charge as it approaches. This corresponds to a negative change in potential energy, hence a negative potential relative to infinity.

Question 4

What's the difference between work done 'by the field' and work done 'on the charge'?

Accepted Answer

Work done 'on the charge' (by an external force) increases its electric potential energy, so $W_{on} = \Delta U = q\Delta V$. Work done 'by the field' decreases the system's potential energy, so $W_{field} = -\Delta U = -q\Delta V$. They are equal in magnitude but opposite in sign. If a charge moves naturally (e.g., repulsion), the field does positive work. If a charge is moved against its natural tendency, an external force does positive work.

Electric potential

What you need to know

Electric potential