AP Phy2 – QAG
1. If you charge a pocket comb by rubbing it with a silk scarf, how can you determine if the comb is
positively or negatively charged?
2. Why does a plastic ruler that has been rubbed with a cloth have the ability to pick up small pieces of
paper? Why is this difficult to do on a humid day?
3. When an electroscope is charged, its two leaves repel each other and remain at an angle. What
balances the electric force of repulsion so that the leaves don’t separate further?
4. Explain why the test charges we use when measuring electric fields must be small.
5. Why can electric field lines never cross?
6. If two points are at the same potential, does this mean that no net work is done in moving a test
charge from one point to the other? Does this imply that no force must be exerted? Explain.
7. State clearly the difference (a) between electric potential and electric field, (b) between electric
potential and electric potential energy.
8. Is there a point along the line joining two equal positive charges where the electric field is zero?
Where the electric potential is zero? Explain.
9. Can two equipotential lines cross? Explain.
10. If V = 0 at a point in space, must
E
= 0? If
E
= 0 at some point, must V = 0 at that point? Explain.
Give examples for each.
11. Can a particle ever move from a region of low electric potential to one of high potential and yet have
its electric potential energy decrease? Explain.
12. When a battery is connected to a capacitor, why do the two plates acquire charges of the same
magnitude? Will this be true if the two plates are different sizes or shapes?
13. If the electric field
E
is uniform in a region, what can you infer about the electric potential V? If V is
uniform in a region of space, what can you infer about
E
?
14. Is the electric potential energy of two isolated unlike charges positive or negative? What about two
like charges? What is the significance of the sign of the potential energy in each case?
15. How does the energy stored in a capacitor change when a dielectric is inserted if (a) the capacitor is
isolated so Q does not change; (b) the capacitor remains connected to a battery so V does not change?
Explain.
16. What quantity is measured by a battery rating given in ampere-hours (A • h)? Explain.
17. Can a copper wire and an aluminum wire of the same length have the same resistance? Explain.
18. The equation P = V 2/R indicates that the power dissipated in a resistor decreases if the resistance is
increased, whereas the equation P = I2R implies the opposite. Is there a contradiction here? Explain.
19. Electric power is transferred over large distances at very high voltages. Explain how the high voltage
reduces power losses in the transmission lines.
