Question

why the direction of electric dipole moment is from negative charge to positive charge?

Answer 1

Think about the external E-field produced by an electric dipole.
E-field lines will originate at the positive charge and end at the negative charge.
The direction of the dipole moment is chosen to give you information about the direction of the external E-field produced by the dipole.

Answer 2

Its a matter of convention, conventionally current flows from the positive terminal to the negative terminal of a voltage source. We know in reality the current flows from negative to positive because charge carriers are negative, electrons, again a convention. Conventions must be used to communicate a phenomenon and generally create a standard way at looking at something. The direction of flux is generally taken from a electron, negative source, toward infinity or a positive source, such as a proton.

Answer 3

hey @Farcher @kenLJW u guys please get to a conclusion whether it is a convention or there is a reason behind it?

Answer 4

It is a convention.
I would aso say that if you has a Gaussian surface around a positive charge the net flux through the Gaussian surface would be positive, this is outwards.