7. The electric potential in a certain region of space is given by $V = -7.5x^2 + 3x$, where $V$ is in
volts and $x$ is in meters. In this region the equipotential surfaces are:
A) unknown unless the charge is given
B) planes parallel to the x axis
C) planes parallel to the yz plane
D) concentric spheres centered at the origin
E) concentric cylinders with the x axis as the cylinder axis
8. If 500 J of work are required to carry a 40-C charge from one point to another, the potential
difference between these two points is:
A) depends on the path
B) none of these
C) 20,000 V
D) 12.5 V
E) 0.08 V
