# How potential energy of electric dipole perpendicular to electric field is zero

1. Sep 28, 2011

### Sumedh

how potential energy of electric dipole perpendicular to electric field is zero
in this situation the torque is maximum
so how P.E. can be zero

2. Sep 28, 2011

### clem

Believe the equation, not your 'intuition'.

3. Sep 28, 2011

### Philip Wood

(1) Potential energy is the work a body can do because of its position. A positive charge a very long way from a negative charge has positive PE relative to when it's near the charge, even though the force acting on it is almost zero when it is far away from the negative charge. There is no logical argument to link high PE of a charge at a point to high force on the charge at that point. Nor, for a dipole, to correlate torque at an orientation with PE at that orientation.

(2) We can assign zero potential energy to any point (or orientation) we wish. It is arbitrary. Only changes in PE have physical significance. It's just kinda neat to assign zero PE to the 'halfway' orientation of the dipole.

Last edited: Sep 28, 2011
4. Sep 28, 2011

### DocZaius

Since the dipole will not move translationally, why would it have anything but zero potential energy?

5. Sep 28, 2011

### Staff: Mentor

Even though the dipole center doesn't translate (at least in a uniform field), the charges do move as the dipole rotates.

6. Sep 28, 2011

### DocZaius

Right - I was aware of that (which is why i was careful to use the word "translationally" for the dipole as a whole). By the way, could we say that the dipole has nonzero electric rotational potential energy? (If we make the zero rotational potential energy to be at the angle when the dipole is parallel with the uniform field)

7. Sep 29, 2011

### Sumedh

Thank you very much
I got it.