The statement is partially correct.
Work Step by Step
The statement is correct for the half-infinite region on the same side of the plane as the positive charge. The field looks exactly the same in that region, with field lines emerging from the positive charge and striking the plane such that the electric field lines are perpendicular to the plane. The statement is incorrect for the region “behind/under” the plane. In the case of the single positive charge and plane, the electric field is zero behind/under the plane. However, in the case of 2 equal and opposite charges, as seen in Figure 23.23b, the electric field lines are on both sides of the plane. The principle, nonetheless, is very useful for some electrostatic problems and is known as the method of images.