- B
The change in potential energy of a point particle, with reference to infinity is given by:
The difference in potential energy between two points is given by:
- B
The electric potential of a charge is given by the equation V = kq/r. In other words, distance is inversely
proportional to electric potential. If the distance is doubled, then the electric potential must be halved.
- D
Excess charges always reside on the surface of a conductor because they are free to move, and feel a
repulsive force from each other.
DC Circuits
IN THE PREVIOUS CHAPTER, WE LOOKED AT the movement of charges, showing that
a net charge creates an electric field with differences in electric potential energy at
different points in the field. When two points in a field with a potential difference are
connected by a conducting material, electrons will flow spontaneously from one point to
another. For instance, when the two terminals of a battery (a source of potential
difference) are connected by a copper wire (a conducting material), electrons flow
spontaneously from the negative terminal of the battery toward the positive terminal.
This mass flow of electrons in a particular direction creates a current, which is the
source of the circuits that we will examine in this chapter.
As fans of hard rock know, there are two kinds of circuits, AC and DC. AC stands for
alternating current: an electromagnetic generator induces a current that alternates in
direction. AC circuits can be quite complicated, so you’ll be relieved to know this is the
last you’ll hear of them: they don’t appear on SAT II Physics. However, you should expect
a good number of questions on DC, or direct current, circuits. These are the more familiar
circuits, where a current flows steadily in a single direction.