Electrostatics Work Book
Name:
Block:
Electric Charge and Electric Field
1.
2.
Read Ch. 16.1 to 16.4 p. 416 to 420.
Write definitions for each of the following:
Static electricity
Electric charge
Unlike charges
Conservation of electric charge
3.
Ion
Conductor
Insulator
Charging by conduction
Charging by induction
Electroscope
Point charge
Elementary charge
Make observations of each of the following demonstrations and give and explanation of each.
a. Electroscope
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b.
Pith Ball
c.
Pith ball Ferry
d.
Van Degraph Generator
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4.
Coulomb
a. What is a Coulomb of Charge?
b.
5.
Elementary Charge
a. What is the elementary charge in coulombs?
b.
6.
Define the magnitude of a coulomb of charge in terms of the magnitude of the meutual
force exerted by two point charges.
How many electrons in one coulomb of charge?
The equation for the force of gravity between two objects is: F 
GMm
r2
The equation for the force of attraction or repulsion between two charges is: F 
kQq
r2
These equations look very similar. How are they similar? Use the principles of physics to explain
why they are similar. k = 8.988x109Nm2/C2 but most calculations we do with k = 9.0x10 9Nm2/C2
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7.
For each of the following find magnitude of the force and state weather it is a force of attraction or
repulsion. Use the length on the page as radius (center to center).
125C
500C
300C
90C
8.
The forces of electrical repulsion or attraction are vectors and are therefore added in the
appropriate manner.
a. Find the force caused by each of the 2 negative charges on the positive charge in the
following diagram.
p
10m
e
4m
2e 
b.
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Draw the vector diagram for the sum of the two forces in part “a” above and give the
resultant force’s magnitude and direction.
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9.
Three charged particles are arranged in a line as shown in the diagram below. Show the net
electrical force on the middle particle as a result of the other two.
0.4cm
-0.8 µC
1.2cm
0.5 µC
-1.2 µC
10. Do Questions 1 – 10 on p. 437.
11. Definition of an electric field
a.
We can use the gravitational field to help us understand an electric field. Write down the
equation for the force of gravity on an object.
b.
We can rewrite this equation as g 
F
. If a small object experiences a big force then
m
the gravitational field must be ________________.
c.
Similarly, an electric field applies a force on an electric charge. Where have you seen
evidence of this?
d.
An electric field is defined as the force exerted on a positive test charge – force per unit
charge.
E
F
q
so the force on a given charge is determined by the
strength of the electric field that it is in at some point in space. F  Eq
e.
Write down the equation for gravitational field strength at some radius from an object.
f.
Predict what the equation for electric field strength at some radius from an object would
be.
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g.
Calculate the charge needed to create an electric field of 3.0 x 10 5 N/C at a distance of
0.3m.
12. Electric field lines always go from positive to negative. The reason for this is that by definition we
use a positive test charge to determine the direction. So obviously a positive test charge will move
away from a positive charge and toward an negative charge. Sketch the field lines for the
following diargeams.
a)
b)

+
c)
+
d)


e)

++
++
++
++
++
++
++
++
++








13. Do #14 – 22, 25, 26 on p. 438
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14. Uniform verses non-uniform fields
a. What is a uniform electric field?
b.
Label the diagram in part 12 that is a uniform field.
c.
What is non-uniform field?
d.
Which of the diagrams of in figure 12 are non-uniform fields?
15. Comparing a Uniform Electric Field to a Gravitational Field Over Small h
Uniform Electric Field
Gravitational Field
+++++++++
b
b
_________a______
-------------
_________a_______
As with gravity only the difference in potential
energies can be calculated. A positive charge would
"want to fall" away from b. So to move a positive
charge from a, which is at a lower potential, to b
requires work.
The change in potential energy of a given mass is
calculated by comparing its potential energy at two
points within an almost uniform gravitational field.
In this example the ground is taken to be zero. To
increase an object’s potential energy you need to
move it up away from the ground. To do this you
must do work to move the object from “a” to “b”.
PE = Fdba
PE = W = Fdba
E
For small
change in h
F
q
Compare #1
g
F
m
W = mgdba
W = qEdba
Voltage
Voltage is defined as the potential energy per unit charge:
Vba 
Note that this is similar to:
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
PEba
m
PEba
q
Note the similarity of the
equations. (The symbol  is
not a proper variable I just
used it for fun.)
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Describe the meaning of .
Describe the meaning of V.
How will you remember what V is?
Substitute the equation for the definition of an electric field into
The answer is
Vba 
PEba
.
q
Vba = Edba
Read Chapter 17-3 Equipotential Lines.
Describe what an equipotential line is.
Compare electric field lines to equipotential lines.
Sketch and label Figure 17-2 and 17-3. Label electric field lines and equipotential lines. Highlight the area
where the electric field is uniform. Explain why the electric field is uniform in these areas.
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Read chapter 17-4
Write a paragraph in which you answer all of the following.
What is an electron volt? How is it defined? What is the purpose of using an eV?
16. Because electric fields around single point charges are non-uniform, we need to come up with an
equation to deal with this situation. Mr.T will lead you through a discussion and notes for this section.
Gravitational Langue
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Electric Language
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a.
What minimum work is required to move a 14C charge from a distance of 5cm to a distance of 0.2cm
from a 20C charge?
b.
If you could manage to place an electron 15m from an oxygen ion an then release it, how fast would
it be moving when it reached a distance of 1.0mm form the ion? Assume no friction.
( Mass of electron = 9.11 x 10 -31Kg, Charge of electron = -1.602 x 10-19 C, O2- = -3.204 x 10 -19C )
17. Do #1 – 10 p. 456
18. CRT and Cathode Ray Tube Notes.
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19. Do # The Cathode Ray Tube Practice Problems Work Sheet
20. Do # 11 to 15 p. 456
21. Do Electrostatics Review Work Sheet
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22. Electro Static Summary
Single Point Charge
Uniform Field
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