Notice that, as with electric field vectors, electric field lines always point away
from positive source charges and toward negative ones. Two equal but opposite
charges, like the ones shown in the previous diagram, form a pair called an electric
dipole.
If a positive charge +q were placed in the electric field above, it would experience
a force that is tangent to, and in the same direction as, the field line passing through
+q’s location. After all, electric fields are sketched from the point of view of what
a positive test charge would do. However, if a negative charge −q were placed in
the electric field, it would experience a force that is tangent to, but in the direction
opposite from, the field line passing through −q’s location.