The equations below support the loss of electric potential and therefore loss of electric potential energy. Since E is constant, it is the change in d for a postive test charge that makes V negative. And therefore, U is negative. Contrarily, a negative charge would gain potential and electric potential energy when it moves in the direction of the field. One other property of a uniform electric field is its equipotential lines.
Equipotential lines are lines on which all points have equal potential.
In a uniform electric field, the equipotential lines are perpendicular to the electric field lines. Two plates of a parallel capacitor are placed 5cm apart. If the potential difference between the plates is 50V, what is the electric field strength.