Download Electric Fields and Forces Review KEY

Ch 17 Electric Fields and Forces Review
1a. When a rubber rod is rubbed with wool, the rod becomes negatively charged. What can you conclude
about the magnitude of the wool's charge after the rubbing process?
It is equal to the magnitude of the rod's charge.
1b. Why did the wool exhibit the Law of Conservation of Charge? Didn't the wool lose it's electrons?
Charge is conserved. According to the Law of Conservation of Charge, charge was transferred from the wool
to the rod.
1c. Rubbing by friction is also called:
.
Triboelectricity
2a. What did Millikan's oil drop experiment reveal about the nature of electric charge?
Charge is quantized
2b. What is the charge of an electron? -1.602 x 10-19 C
What is the charge of a proton? 1.602 x 10-19 C
3. If you were to stick a piece of transparent tape on your desk and then quickly rip it off, you will find that the
tape is attracted to other areas of your desk and yourself that are not charged. Why does this happen?
Charging by contact?
Charging by induction?
Charging by Triboelectricity?
Explain your choice…..Charging by Triboelectricity. The tape induces a surface charge on itself and the desk
and becomes polarized.
4a. Metals, such as copper and silver, can become charge by induction, while some plastic materials cannot.
Why does this occur?
Plastics is an insulator, does not conduct electricity as easily.
4b. How are conductors different from insulators?
Conductors transfer charges easily, insulators do not.
5.
This picture shows the effect of Triboelectricity. What effect is being shown?
Polarization
6. The dome of a Van de Graaff generator receives a charge from the revolving leather belt. What would be
the apparent magnitude of the electric field strength:
a. inside the dome?
NO CHARGE INSIDE THE DOME
b. at the surface of the dome? Equal to the amount of charge conserved given by the leather belt.
c. 1 meter away from the dome?
Use the Electric Field Strength equation
7. The gravitational force is always attractive, while the electric force is both attractive and repulsive. What
accounts for this difference?
Mass is positive, charges are positive and negative.
8a. How does the electric force between two charges change when the distance between them is doubled?
The force becomes ¼ the initial value according to the Inverse Square Law.
8b. How does it change when the distance is halved?
Ch 17 Electric Fields and Forces Review
The force becomes four times the initial value according to the Inverse Square Law.
9. What determines the direction of the electric force between two charges?
The signs of the charges.
10. Identify examples of electric forces in everyday activities
Forces between brushes and hair, shocks occurring when sliding off of chairs and touching metals…answers
will vary.
11. Observe the electric field lines below. Rank the objects according to which has the greatest magnitude of
electric charge, beginning with the smallest charge.
Rank order is: G < E < F
the principle is that objects with the greatest charge will have the greatest
number of lines emanating from it or approaching it.
12. Draw the lines of force representing the electric field around a single isolated positive charge.
13. Draw the lines of force which would be present around two negative charges
14. A small cork with an excess charge of +6.0 μC is placed 0.12 m from another cork, which carries a charge of
−4.3 μC. What is the magnitude of the electric force between the corks?
−1.93 N
15. A charge Q is at origin, and a test charge q2 = -5.0 nC is on the y-axis 0.300 m up from origin. Find the
electric field strength at q2?
−499.44 N/C towards Q
16. What is the electric force on a glass ball that is in an electric field of +2.5 N/C with a point charge of
−5.0 mC acting upon it.
−0.0125 N