Download Electrostatics Test Review

Name:_________________________________
Date:_____________________________
Electrostatics Test Review 11-12
All work must be shown, including givens, equations used, and units. Draw diagrams as appropriate.
This review must be handed in on the day of your test, and will be worth 5 test points.
1. If a charged rod A attracts another rod B, you can conclude that
a. Rod B is also charged with the opposite charge
b. rod B is uncharged
c. Either of answers a or b may be correct; you cannot tell for sure.
2. If two charged balloons repel,
a. Both balloons are charged, and have like charge
b. Both balloons are charged, and have unlike charge
c. One of the balloons could be uncharged.
3. If you charge a conductor by touching it with a charged object, what kind of charging process is this? Does
the conductor develop the same sign of charge as the charging object or the opposite sign?
4. If you charge a conductor by bringing a charged object near it without touching it and then grounding it,
what kind of charging process is this?
5. An object becomes negatively charged because it has
a. An excess of electrons
b. A lack of electrons.
6. If you charge a conductor by induction, by bringing a negatively charged rod close to it, followed by
grounding, what is the sign of the charge induced on the conductor?
7. You want to place a negative charge on a conductor, by the process of induction. Draw the steps of the
process.
2
q1q2
q
9 Nm
Fe  k 2 , Fe  qE, E  k 2 , k  9.0 10
, qe  e 1.6 1019 C
2
r
r
C
Name:_________________________________
Date:_____________________________
8. The electric field 2m away from a positive charge is 20 N/C. What is the field 6m away from the charge?
(2.22 N/C)
9. Marie charges two balloons by rubbing them against her hair. Both the balloons have an equal charge Q. When
Marie holds the two balloons 3.0m apart, they repel each other with a force of 2.5N. Find the charge Q on
the balloons. (5.0X10-5 C each)
10. A 3.5 μC charge is placed 2 cm to the left of a -2.5 μC charge and a 3.0 μC charge is placed 4 cm to the right
of the -2.5 μC charge. Find the net force on the 3.5 μC charge.(171N to the right)
2 cm
3.5 μC
4 cm
–2.5 μC
3.0 μC
2
q1q2
q
9 Nm
Fe  k 2 , Fe  qE, E  k 2 , k  9.0 10
, qe  e 1.6 1019 C
2
r
r
C
Name:_________________________________
Date:_____________________________
11. A 3.5 μC charge is placed 0.2m to the north of a -2.5 μC charge and a 3.0 μC charge is placed 0.4m to the
west of the -2.5 μC charge. Find the net force on the -2.5 μC charge and indicate its direction.(2.01N,
@ 77.90 N of W )
3.5 μC
0.2m
3.0 μC
0.4m
-2.5 μC
12. Three charges are placed along the y-axis as follows. A -2.5 μC is placed at the origin, a 3.0 μC is placed at
+1.5m, and a 4.5 μC is placed at + 4.0m. Find the net electric force on the 3.0 μC charge. (.0494 N down)
4.5μC
y=4.0m
y= 1.5m
3.0 μC
y=0
–2.5 μC
2
q1q2
q
9 Nm
Fe  k 2 , Fe  qE, E  k 2 , k  9.0 10
, qe  e 1.6 1019 C
2
r
r
C
Name:_________________________________
Date:_____________________________
13. The Van de Graaf generator in Rm. 232 develops a charge of 2C. If the electric force on a 1C charge at Matt’s
desk is 4.5X109 N, how far is Matt’s desk from the generator? (2.0m)
14. Are you safe if you stay in your car during a lightning storm? Justify your answer.
15. In winter I get an electrical shock when I touch the doorknob of Rm. 320. This happens
because -2.5 μC of charge flow from the doorknob into my fingers. How many electrons flow into
my fingers?(1.5625X1013 electrons)
16. True or False?
a. Electric field lines start at negative charges and end at positive charges or at infinity.
b. Electric field lines start at positive charges and end at negative charges or at infinity.
c. Electric field lines can cross each other.
d. Electric field lines show the direction in which a positive charge would move.
e. The electric field vector at any point is tangential to the field line at that point.
f. The electric field is strongest where the number of field lines are the least.
e. Negative charges move in the same direction as positive charges move in an electric field.
2
q1q2
q
9 Nm
Fe  k 2 , Fe  qE, E  k 2 , k  9.0 10
, qe  e 1.6 1019 C
2
r
r
C
Name:_________________________________
Date:_____________________________
17. For the field map in the figure below, draw the electric field vector at points A and B. Are the charges
q1 & q2 negative or positive? How do you know?
A
q1
q2
B
18. a. An electron in a cathode ray tube experiences a force of 30 N. Find the electric field inside the cathode ray
tube. (The charge of an electron is 1.6X10-19 C).(1.875X1020N/C)
b. Find the acceleration of the electron. (The mass of an electron is 9.11X10-31 Kg). (3.29X1031 m/s2)
c. If the electron starts from rest, how long does it take to travel a distance of 100m? (2.46X10-15 seconds)
2
q1q2
q
9 Nm
Fe  k 2 , Fe  qE, E  k 2 , k  9.0 10
, qe  e 1.6 1019 C
2
r
r
C