Download Electrostatics Problem Set

Electrostatics Problem Set
1. Define/explain each of the following terms.
a. Insulator
d. Elementary charge
b. Conductor
e. One coulomb
c. Semiconductor
f. Electroscope
2. Rosie needs to charge an object by conduction, and Eva needs to charge another object by
induction. Explain to each student what she must do using diagrams. Explain how to
charge (the nearest end of) each object both positively and negatively.
3. Why would your hair stand on end if you were touching the ball on a Van der Graaf
generator? Use a diagram and explain the flow of charges. Use your text if needed.
4. Object A has a charge of +1.8 µC and object B has a charge of -1.0 µC. They are 14 mm
apart. What is the force on A? What is the force on B?
5. Three particles are placed in a line. The left particle has a charge of -67 µC, the middle
one has a charge of +45 µC, and the right one has a charge of -83 µC. The middle particle
is 72 cm from each of the others. Find the net force on (a) the middle particle, (b) the
right particle.
6. Two small charges, +40 µC and -18 µC, are placed 24 cm apart. What is the force on a
third small charge, of magnitude -2.5 µC, if it is placed on the line joining the other two,
and
a. 12 cm to the outside of them, on the side of the negative one?
b. 12 cm to the outside of them, on the side of the positive one?
c. Midway between them?
1.0 m
7. Find the net force on Q1 in the
Q1 = 22 µC
Q5
Q2
diagram at the right. Then find the
Q2 = 11 µC
force on Q3 also.
Q3 = 12 µC
Q4 = 13 µC
8. A lead nucleus (say it out loud:
Q5 = 14 µC
Q1
1.0 m
NOO-clee-us, NOT nookyoolus )
contains 82 protons. Find the force
experienced by a 1.5 µC charge at a
point 10.0 nm from the nucleus.
Q4
Q3
9. One model of the structure of the hydrogen atom consists of a stationary proton with an
electron moving in a circular path around it, of radius 5.3 × 10-11 m. The masses, charges
and other necessary data can be found on the inside cover of your text.
a. What is the electrostatic force between the proton and the electron?
b. What is the gravitational force between them?
c. Which force is mainly responsible for keeping the electron in orbit around the
proton? Prove your answer by showing that one force is a certain number of
times the other.
d. Calculate the velocity and period of the electron’s orbit.
Answers:
4.) 83 N each [towards the other]; 5.) a) 13 N [right], b) 41 N [left]; 6.) a) 21 N [away from neg], b) 59
N [towards pos], c) 91 N [towards pos]; 7.) 1.0 N [right], 7.3 N [44 down from right]; 8.) 1800 N; 9.)
a) 8.2 × 10-8 N, b) 3.6 × 10-47 N, c) electrostatic is 2.4 × 1039 times the grav., d) 2.2 × 106 m/s,
1.5 × 10-16 s