Why is the dipole moment vector directed from negative to positive charge?

[thunderhadron]

Hi friends as all know that the direction of electric dipole moment vector is from negative charge towards the positive charge. I am pretty confuse that this direction is allotted to the dipole moment vector with some reason or just by convention.

 

[Simon Bridge]

Mostly by convention - it is done this way to make the signs consistent with the rest of physics.

 

[tiny-tim]

hi thunderhadron!

yes, it seems anomalous …

the polarisation field P is the sum of the electric dipole moments p, and:

∇·E = ρ_total/ε_o
∇·D = ρ_free
but
∇·P = -ρ_bound​

because of that, we have D = e_oE + P, making it looks as if D is the total electric field, instead of E

(also, it means that the energy of an electric dipole p in an electric field E is minus p·E)​