An electric dipole is placed in a uniform electric field at some angle, say 90 degrees. The dipole consists of 2 charges, one negative and one positive. The charge which is positive will have a torque which is in the direction of the field and the negative charge will have a torque opposite to the direction of the field. Now my question is what determines the direction of torques. Why is the direction of torque due to negative charge opposite to the direction of electric field ? Why can't it be in the same direction like the positive charge?
Also, if the dipole is placed in a non-uniform field, how do we determine the direction of the force acting on the negative and positive charges of dipole?