Physics 1010

Question Set 11

Review Questions: Electrostatics

Answers



1. Two charged particles held near each other are released. As they move, the acceleration of each decreases. Therefore, the particles have

A. the same sign.
B. opposite signs.
C. not enough information given.

Reasoning: They must berepelling each other. Thus they move away, and as they do, the force on each charges keeps decreasing, which results in a decrease in acceleration.

2. A positive charge and a negative charge held near each other are released. As they move, the force on each particle

A. increases.
B. decreases.
C. stays the same.

3. In an electrically neutral atom the number of protons in the nucleus is equal to the number of

A. electrons that surround the nucleus.
B. neutrons in the nucleus.
C. both of these.
D. neither of these.

4. A positive ion has more

A. electrons than neutrons.
B. electrons than protons.
C. protons than electrons.
D. protons than neutrons.
E. neutrons than protons.

5. Strip electrons from an atom and the atom becomes a

A. positive ion.
B. negative ion.
C. different element.

6. To say that electric charge is quantized is to say that the charge on an object

A. may occur in an infinite variety of quantities.
B. is a whole-number multiple of the charge of one electron.
C. will interact with neighboring electric charges.
D. can be neither created nor destroyed.

7. To say that electric charge is conserved is to say that electric charge

A. may occur in an infinite variety of quantities.
B. is a whole number multiple of the charge of one electron.
C. will interact with neighboring electric charges.
D. can be neither created nor destroyed.

8. The unit of electric charge, the coulomb, is the charge on

A. one electron.
B. a specific large number of electrons.


9. A main difference between gravitational and electric forces is that electrical forces

A. attract.
B. repel or attract.
C. obey the inverse-square law.
D. act over shorter distances.
E. are weaker.

10. The electrical force between charges is strongest when the charges are

A. close together.
B. far apart.
C. the electric force is constant everywhere.

11. The electrical force between charges depends on the

A. magnitude of electric charges.
B. separation distance between electric charges.
C. both of these.
D. none of these.

12. Rub electrons from your hair with a comb and the comb becomes

A. negatively charged.
B. positively charge.

13. An electroscope is charged positively as shown by foil leaves that stand apart. As a negative charge is brought close to the electroscope, the leaves

A. fall closer together.
B. spread apart further.
C. do not move.

14. Two protons attract each other gravitationally and repel each other electrically. By far the greater is

A. the gravitational attraction.
B. the electrical repulsion.
C. neither - they are the same.

15. The primary purpose of a lightning rod is to

A. attract lightning and guide it to the ground.
B. discharge the structure to which it is attached.
C. cancel the electric field within the structure to which it is attached.
D. induce within the structure to which it is attached a charge opposite to that of charged clouds overhead.

16. A balloon will stick to a wooden wall if the balloon is charged

A. negatively.
B. positively.
C. either way.
D. neither way.

17. When a car is struck by lightning, the resulting electric field inside the car is

A. normally huge, but for a brief time.
B. normally huge for a time longer than the lightning stroke itself.
C. small enough to be safe for an occupant inside.
D. zero.

18. Electric potential, measured in volts, is the ratio of electric energy to amount of electric

A. current.
B. resistance.
C. charge.
D. voltage.
E. none of these.

19. An uncharged pith ball is suspended by a nylon fiber. When a negatively charged rubber rod is brought nearby, without touching it, the pith ball

A. becomes charged by induction.
B. becomes polarized.
C. is repelled by the rod.
D. all of these.
E. none of these.

20. When the distance between two charges is halved, the electrical force between the charges

A. quadruples.
B. doubles.
C. halves.
D. is reduced by 1/4.
E. none of these.

21. Particle A and Particle B interact with each other. Particle A has twice the charge of particle B. Compared to the force on Particle A, the force on Particle B is

A. four times as much.
B. two times as much.
C. the same.
D. half as much.
E. none of these.

Reasoning: Newton's 3rd law requires the forces to be the same but in opposite direction. Also, based on the Coulomb's law, the force depends on both charges and thus is the same for the two charges.

22. If you comb your hair and the comb becomes positively charged, then your hair becomes

A. positively charged.
B. negatively charged.
C. uncharged.

23. A difference between electric forces and gravitational forces is that electrical forces include

A. separation distance.
B. repulsive interactions.
C. the inverse square law.
D. infinite range.
E. none of these.

24. A conductor differs from an insulator in that a conductor

A. has more electrons than protons.
B. has more protons than electrons.
C. has more energy than an insulator.
D. has faster moving molecules.
E. none of these.

Reasoning: Insulators have tightly bound electrons. Conductors have a large number of (almost) freely moving electrons. In both cases, the number of electrons and protons are normally the same, because atoms are neutral.

25. Every proton in the universe is surrounded by its own

A. electric field.
B. gravitational field.
C. both of these.
D. none of these.