Name
Electrostatics Worksheet
In this worksheet if you see any charge or draw any charge, only excess charge is shown. If there are no plus (+) or minus (-)
symbols then the object or area has an equal number of each (is neutral).
1.
The balloon has been rubbed on Sue D. Nym’s head and then hung from the ceiling.
A negatively charged rod is brought close to the balloon and the rod repels the balloon.
a)
What charge does the balloon have? The balloon has a negative (-) charge
since the balloon was repelled by a negative.
b) What is this method of charging called? Charge by friction (triboelectric effect)
c)
How do you know this? Two materials were rubbed together and they are now charged.
d) What was the type of charge on Sue’s hair immediately after the balloon was rubbed on it? Positive +
e)
2.
Explain how her hair gained this charge? When her hair was rubbed on the balloon it lost electrons to the
balloon. That left her hair with an excess of positive charge.
The positively charged metal globe X on the end of the insulating handle is brought over and touched to neutral globe Y,
another metal globe on an insulated post.
a) On the diagram to the right, sketch the charges on the two globes after they are touched and moved apart.
X
X
Y
Y
b) What is this method of charging called? Charge by conduction
3. This time the globe X is brought near, but does not touch globe Y. While globe X is held near, a finger is touched to the far
side of globe Y. The finger is then taken away, and then globe X is pulled back.
a) On the diagram to the left, sketch the charges on globe Y before it is touched with the finger.
b) On the diagram to the right, sketch the charge on the two globes after they are separated. (They are far enough apart not
to affect each other.)
E
X
Y
c)
What is this method of charging called? What steps are involved?
Charge by induction
polarization and grounding
X
Y
4.
Two initially uncharged metal spheres are in contact with each other and resting on insulating posts as shown below. A
negatively charged balloon is brought near, and while it held nearby, sphere B is moved to the right by sliding the base
sideways. The balloon is then removed.
a) On the diagram to the left, sketch the charges on the two globes before they are separated.
b) On the diagram to the right, sketch the charge on the two globes after they are separated. (They are far enough apart not
to affect each other.)
A
c)
5.
A
B
What charge do A and B have after separation?
A is positive and B is negative
B
d) By what method were the spheres charged?
polarization (and separation?) induction?
We have four electroscopes with an unknown charge state. We take a plastic rod and rub it with plastic such that it becomes
positively charged. The rod is brought in contact with electroscope 2. Now the electroscopes are brought toward each other.
1, 3, and 4 are all attracted to 2. 1 and 3 have no effect on each other. 1 and 3 are both attracted to 4. What are the charge
states of 1, 2, 3, and 4? Explain your reasoning.
2 is positive – it was charged by conduction and then
repelled by a + charge so it must be positive
1 and 3 are neutral – they had no effect on each other
so there is no other choice
1
2
3
4
4 is negative – it was attracted to 2 so it must be
negative or neutral. It attracted neutral objects so it
must be negative.
6. A negatively charged rod is bought close to a neutral electroscope and the electroscope is attracted to the rod, touches the rod
and is then repelled by the rod. Why was the electroscope attracted to the rod? What charge does the electroscope have
before it touches the rod? After it touches the rod?
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The electroscope was attracted to the rod because the rod polarized the electroscope. The electroscope has no charge
before the rod touches it. After the rod touches the electroscope the electroscope is negative due to charge by
conduction.
7. The base of an electrophorus, a piece of styrofoam is rubbed with rabbit fur. The styrofoam is then lifted and brought close to
a leaf electroscope. The electroscope leaves spread apart.
a) What does this prove about the styrofoam? What charge does it have?
This step proves the Styrofoam is charged as
it polarized the electroscope.
At this time you do not know the charge on
the Styrofoam.
b) The top plate of the electrophorus (made of aluminum with an insulated handle) is placed on the electrophorus base. It is
then lifted up and touched to the leaf electroscope. It has no effect on the electroscope. What does this tell you about the
charge on the top of the electroscope?
This shows the top of the
electroscope is not charged as
no charge is conducted to the
electroscope.
c)
The top is set back on the base and touched with a finger. Then the top is picked up and touched to an electroscope after
which it is repelled by the electroscope. After that a positive rod is brought close to the electroscope and it is repelled.
What charge did the top of the electrophorus have when picked up off the styrofoam? How do you know? What moved,
and from what to what when the finger touched the edge of the plate?
E
+++++++++++++
The top is positive. You know this because when the electroscope is charged by
conduction from the top it has the same charge as the top. The electroscope is then
repelled by a + charge so it must be positive.
d) You should now know the charge of each object in each part. Draw in the areas of excess charge on each object below.
The fur in part A
The fur is positive
and the Styrofoam
is negative. Because
they are insulators
there is only charge
where they were
rubbed together.
The top is positive
as electrons were
repelled by the
Styrofoam causing
the electroscope to
become polarized.
The styrofoam in part A
The electroscope in part A
(while the styrofoam base is held close)
The top is polarized
due to the negative
charge on the base.
The base and top of the electrophorus in part B
The top is now
positive as the
finger allowed
electrons to leave
the rim of the pan.
The top of the electrophorus in part C
(after lifted off the base)