Page 837 - College Physics For AP Courses

Chapter 18 | Electric Charge and Electric Field
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67. Construct Your Own Problem
Consider two insulating balls with evenly distributed equal and opposite charges on their surfaces, held with a certain distance between the centers of the balls. Construct a problem in which you calculate the electric field (magnitude and direction) due to the balls at various points along a line running through the centers of the balls and extending to infinity on either side. Choose interesting points and comment on the meaning of the field at those points. For example, at what points might the field be just that due to one ball and where does the field become negligibly small? Among the things to be considered are the magnitudes of the charges and the distance between the centers of the balls. Your instructor may wish for you to consider the electric field off axis or for a more complex array of charges, such as those in a water molecule.
68. Construct Your Own Problem
Consider identical spherical conducting space ships in deep space where gravitational fields from other bodies are negligible compared to the gravitational attraction between the ships. Construct a problem in which you place identical excess charges on the space ships to exactly counter their gravitational attraction. Calculate the amount of excess charge needed. Examine whether that charge depends on the distance between the centers of the ships, the masses of the ships, or any other factors. Discuss whether this would be an easy, difficult, or even impossible thing to do in practice.
Test Prep for AP® Courses
18.1 Static Electricity and Charge: Conservation of Charge
1. When a glass rod is rubbed against silk, which of the following statements is true?
a. Electrons are removed from the silk.
b. Electrons are removed from the rod.
c. Protons are removed from the silk.
d. Protons are removed from the rod.
2. In an experiment, three microscopic latex spheres are sprayed into a chamber and become charged with +3e, +5e, and −3e, respectively. Later, all three spheres collide simultaneously and then separate. Which of the following are possible values for the final charges on the spheres? Select two answers.
3. If objects X and Y attract each other, which of the following will be false?
a. X has positive charge and Y has negative charge. b. X has negative charge and Y has positive charge. c. X and Y both have positive charge.
d. X is neutral and Y has a charge.
4. Suppose a positively charged object A is brought in contact with an uncharged object B in a closed system. What type of charge will be left on object B?
a. negative
b. positive
c. neutral
d. cannot be determined
5. What will be the net charge on an object which attracts neutral pieces of paper but repels a negatively charged balloon?
a. negative
b. positive
c. neutral
d. cannot be determined
6. When two neutral objects are rubbed against each other, the first one gains a net charge of 3e. Which of the following statements is true?
a. The second object gains 3e and is negatively charged.
b. The second object loses 3e and is negatively charged.
c. The second object gains 3e and is positively charged.
d. The second object loses 3e and is positively charged.
7. In an experiment, a student runs a comb through his hair several times and brings it close to small pieces of paper. Which of the following will he observe?
a. Pieces of paper repel the comb.
b. Pieces of paper are attracted to the comb.
c. Some pieces of paper are attracted and some repel the
comb.
d. There is no attraction or repulsion between the pieces of
paper and the comb.
8. In an experiment a negatively charged balloon (balloon X) is repelled by another charged balloon Y. However, an object Z is attracted to balloon Y. Which of the following can be the charge on Z? Select two answers.
a. negative
b. positive
c. neutral
d. cannot be determined
XYZ
(a) +4e −4e +5e (b) −4e +4.5e +5.5e (c) +5e −8e +7e (d) +6e +6e −7e