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Quiz: Electrostatics
1. An electroscope is a device with a metal knob, a
metal stem, and freely hanging metal leaves
used to detect charges. The diagram below
shows a positively charged leaf electroscope.
As a positively charged glass rod is brought near
the knob of the electroscope, the separation of
the electroscope leaves will
(1) decrease
(2) increase
(3) remain the same
2. As shown in the diagram, a neutral pith ball suspended on a string is attracted to a positively
charged rod.
During contact with the rod, the pith ball
1. become negatively charged by gaining electrons
2. become negatively charged by losing protons
3. become positively charged by gaining protons
4. become positively charged by losing electrons
3. The electrostatic force between two positive point charges is F when the charges are 0.1 meter
apart. When these point charges are placed 0.05 meter apart, the electrostatic force between them
is
1. 2F
2. ½ F
3. 4F
4. ¼ F
4. When a plastic rod is rubbed with wool, the plastic acquires a negative charge because
1. electrons are transferred from the wool to the rod
2. protons are transferred from the wool to the rod
3. electrons are transferred from the rod to the wool
4. protons are transferred from the rod to the wool
5. Two plastic rods, A and B, each possess a net negative charge of 1.0 × 10-3 coulomb.
The rods and a negatively charged sphere are positioned as shown in the diagram. Which
vector below best represents the resultant electrostatic force on the sphere?
1.
2.
3.
4.
Questions 6 and 7 refer to the following diagram which represents two small, charged, identical
metal spheres, A and B that are separated by a distance of 2.0 meters.
6. What is the magnitude of the electrostatic force exerted by sphere A on sphere B?
(1) 7.2 × 10−3 N
(3) 8.0 × 10−13 N
−3
(2) 3.6 × 10 N
(4) 4.0 × 10−13 N
7. If the two spheres were touched together and then separated, the charge on sphere A would be
(1) −3.0 × 10−7 C
(3) −1.3 × 10−6 C
−7
(2) −6.0 × 10 C
(4) −2.6 × 10−6 C
8. A positively charged rod is held near the knob of a neutral electroscope. Which diagram below
best represents the distribution of charge on the electroscope?
1.
3.
2.
4.
9. A negatively charged plastic comb is brought close to, but does not touch, a small piece of
paper. If the comb and the paper are attracted to each other, the charge on the paper
1. may be negative or neutral
2. may be positive or neutral
3. must be negative
4. must be positive
10. Gravitational forces differ from electrostatic forces in that gravitational forces are
(1) attractive, only
(2) repulsive, only
(3) neither attractive nor repulsive
(4) both attractive and repulsive
11. During a lightning storm, most cars can provide safe shelter because cars
1. have rubber tires.
2. repel static charges.
3. are metal containers.
4. have antennas.
12. Moving 4.0 coulombs of charge through a circuit requires 48 joules of electric energy. What
is the potential difference across this circuit?
(1) 190 V
(3) 12 V
(2) 48 V
(4) 4.0 V
13. The electronvolt is a unit of
(1) energy
(3) electric field strength
(2) charge
(4) electric potential difference
Free Response
14. Two similar metal spheres, A and B, have charges of +2.0 × 10-6 coulomb and +1.0 × 10-6
coulomb, respectively, as shown in the diagram below. The magnitude of the electrostatic force
on A due to B is 2.4 newtons.
[a] What is the magnitude of the electrostatic force on B due to A?
[b] Calculate the distance between spheres A and B? Show equation and substitution with units.
[2]
[c] If A and B are connected with a metal wire, what will be the magnitude of the charge left on
sphere B?
15. Two conducting parallel plates 5.0 × 10−3 meter apart are charged with a 12-volt potential
difference. An electron is located midway between the plates. The magnitude of the electrostatic
force on the electron is 3.8 × 10−16 newton.
a. On the diagram above, draw at least three field lines to represent the direction of the
electric field in the space between the charged plates.
b. Identify the direction of the electrostatic force that the electric field exerts on the electron.
c. Calculate the magnitude of the electric field strength between the plates, in newtons per
coulomb. [Show all work, including the equation and substitution with units.] [2]
d. Describe what happens to the magnitude of the net electrostatic force on the electron as the
electron is moved toward the positive plate.
16. Which diagram represents the electric field between two oppositely charged conducting
spheres?