Chapter Questions
When you rub two transparencies with tissue and hold them close together, they stand apart. Give two reasons that the force causing this cannot be gravity.
Suppose that you rub a transparency with a tissue to charge both objects and then hold them several meters apart and shake both of them back and forth. Name the forces that they exert on each other.
Cite the evidence supporting the claim that there are two, and only two, types of electric charge.
since matter is made of electrically charged particles, why don't we and the objects around us feel electric forces all the time?
When you remove a wool dress from a garment bag, the sides of the bag might tend to stick to the dress. Explain.
Suppose that the electric force between two objects is $2 \mathrm{N}$ and that you then double the distance between the objects. What is the new force?
Figure 17 shows an electroscope. The leaves (made of metal foil) normally hang down, but they spread apart when the metal sphere on top touches a charged object. Explain.
Suppose that the electric force between two objects is $2 \mathrm{N}$ and that you then double the electric charge on each object. What is the new force?
Describe at least two ways in which the gravitational force and the electric force differ.
How does the operation of the electroscope (previous exercise) demonstrate electric current?
In what ways are the electric and gravitational force laws similar?
When tiny scraps of paper are placed between two flat metal plates that have been oppositely charged (one plate charged positively and the other charged negatively), they bounce back and forth between the plates. Explain this phenomenon.
Highway trucks can become electrically charged as they travel. How can this happen? This can be dangerous, especially for gasoline tank trucks. How can it be prevented?
List the types of particles that are found within the atom.
What happens to the electric force between two charged objects if the charge on one of them is reversed in sign?
What happens to the electric force between two charged objects if the charges on both of them are reversed in sign?
Ping pong ball A has an electric charge that is 10 times larger than the charge on ping pong ball B. When placed sufficiently close together to exert measurable electric forces on each other, how does the force by A on B compare with the force by $\mathrm{B}$ on $\mathrm{A} ?$
Objects A and B are both electrically charged. If the distance between them is halved while the charge on $\mathrm{A}$ is also halved, what happens to the force between them?
If the distance between two charged objects is reduced to one-fourth of its original value, what happens to the electric force between them?
If the distance between two charged objects and the charge on each of them are all doubled, what happens to the electric force between them?
While brushing your hair, you find that the hairs tend to stand apart from one another and that they are attracted toward the brush. Explain this in microscopic terms.
A covered mystery shoebox is placed on a table. What are a few ways that you could learn something about its contents without directly touching it or having it lifted?
After you walk across a rug and scuff electrons off the rug, are you positively or negatively charged?
According to Figure $3,$ what are the atomic numbers of carbon and helium? Roughly how much more massive is the carbon atom than the helium atom?
Some science fiction stories portray atoms as true miniature solar systems populated by tiny creatures. What are some differences, other than size, between our solar system and the planetary model of an atom?
An atom loses its two outermost electrons. How does the resulting ion behave when it is near a positively charged transparency? A negatively charged tissue?
In the preceding question, would anything be different if it lost only one electron?
MAKING ESTIMATES About how many atoms thick is a sheet of paper?
MAKING ESTIMATES Which is bigger, an atom or a wavelength of light? Roughly how much bigger?
Is a wire that carries current electrically charged?
At what point or points in the circuit of Figure 8 do electrons have the least energy? What kind of energy?
Does more current flow out of a battery than into it?
Only a small fraction of the electric energy that is used up in an incandescent light bulb is transformed into light. What happens to the remaining energy?
In the circuit of Figure $8,$ would a thicker lightbulb filament produce a larger current, smaller current, or neither? Explain.
Do the headlights of an automobile carry AC or DC? What about a toaster in your kitchen?
The filament of a lightbulb glows, while the connecting wires do not. Why?
Do the electric circuits in your home produce magnetic fields? Suggest a measurement that might check your answer.
Is an electric field a form of matter? Explain. What about a oravitational field?
A proton is placed, at rest, at some point $A$ within a room that is otherwise devoid of all matter. At some other point $\mathrm{B}$ within the room is there an electric field? An electric force? A magnetic field? A magnetic force? Is there energy at point B?
Suppose that, in the preceding exercise, the proton is oscillating back and forth. Is there an electric field at point B? An electric force? A magnetic field? A magnetic force? Energy?
Suppose you have a piece of metal wire and a bar magnet. Describe two ways in which you could create an electric current. What law of physics is involved here?
You have three iron bars, only two of which are permanent magnets. Because of temporary magnetization, all three bars at first appear to be magnetized. How can you determine which one is not magnetized, without using any other objects?
Suppose you have two iron bars (see the previous exercise), one magnetized and one not magnetized. Can you then determine which one is magnetized, without using any other objects?
If you place a proton at some point in an electric field and then release it, what will happen?
How would a proton's motion differ from the motion of an electron placed at the same point in the same electric field?
How would a proton's motion differ from the motion of an electron placed at the same point in the same gravitational field?