Why is the direction of Electric Dipole moment taken from negative to positive charge?

 

In the moment of force, we see the direction of $\vec{r}$ is taken from the center to the point (radially outwards).

In the moment of couple, we see the direction of $\vec{r}$ is taken from -F to +F. Only if it is taken in this way, the $\vec{\tau}=\vec{r}\times\vec{F}$ the direction of the torque will go into the paper, which is the correct direction of rotation for the given forces.

A similar approach for Electric Dipole moment $\vec{p}$ shows us that, only if the direction is taken from -q to +q, the direction of the torque will go into the paper, which is the correct direction of rotation for the forces shown.

\(\vec{\tau}=\vec{r}\times\vec{F}\)

\(\hspace{1cm}=\vec{r}q\times\frac{\vec{F}}{q}\)

\(\hspace{1cm}=2\vec{a}q\times\vec{E}\)

\(\)

\(\vec{\tau}=\vec{p}\times\vec{E}\)