CATCHING A CHARGE
Grades 9 - 12
This lesson introduces the concepts of electrical induction
and conduction and the effects of each on an electroscope. The students
should construct and use a simple electroscope and use the device to discover
how charges affect an electroscope. The lesson integrates hands-on techniques
with video animation. The students should use video segments to observe
how charges move within electroscopes. In the post-viewing activity the
students should be able to determine the charge of an unknown material based
on the response of the electroscope.
"ELECTRICITY #2: Charging and Discharging"
"ELECTRICITY #3: Charging by Induction"
Students will be able to:
- build an electroscope;
- define the function of an electroscope;
- describe the motion of charges inside an electroscope when touched
- charge object (conduction);
- describe the motion of charges inside an electroscope when a charged
- is brought near an electroscope (induction);
- define and give an example of charging by conduction;
- define and give an example of charging by induction; and
- identify an unknown charge based on the motions of a charged electroscope.
Each pair of students will need:
- Viewing activity worksheet
- Instruction Sheet: Making an Electroscope
- small Jar (10 oz or larger)
- 5-inch by 5-inch piece of aluminum foil
- paper clip
- two strips of aluminum foil approximately 1.5- inch by 0.25-inch
- adhesive tape
- glass rod
- rubber rod
- cardboard (the size of the jar opening)
Immediately upon entering the classroom, blow up a balloon,
rub it against a piece of wool, and stick the balloon to a wall. Ask the
students, "Why does the balloon stick to the wall?" Once an answer
of static electricity is reached, ask the students how they know static
electricity is holding the balloon to the wall, can they observe an electrical
charge? Explain to the students that we will be learning about static electricity
today and how different charges affect each other. Since actual charges
are too small for us to see, we will be using video and building a device
called an electroscope to help us study the properties of charges.
To give the students a specific responsibility while viewing
the video, have them list the motion of electrons and protons in a metal
conductor and determine their motion.
START the video, Electricity #2, Changing and Discharging
at the point immediately after the man with the electric charge touches
the sink in the beginning of the section.
PAUSE the video when the positive ions are vibrating. Call on a student
to describe the motion of the particles. Distribute the viewing worksheet
at this point and have the students answer the first two questions. Have
the other students in the class copy the answer into their worksheets. Pausing
the video at this point, then allows the students to ask and discuss questions,
and gives an opportunity to refocus the students' attention on the next
Tell the students to observe in the next video segment and list in their
worksheets which particle transfers charge.
RESUME the video segment.
PAUSE the video segment after the narrator states electrons transfer
charge. The students should make note of the motion of the charges between
the two materials. PAUSE the video when the cotton has a -1 charge.
Pausing at this point allows students to hypothesize about the charge on
the other object. Ask the students, from what they already know about static
electricity, what would they believe the charge on the wool to be, if any.
The students should be able to hypothesize that since the wool lost electrons,
it now has more protons than electrons and now would be positively charged.
Ask the students what would happen if the cotton and the wool continue to
rub against each other. Most of the students will answer that the charge
on each increases. Instruct them to compare what happens on the next video
segment to their answer.
RESUME the video.
PAUSE the segment when they reach a charge of 5, -5. Ask the students
if they think there is a limit to how large a charge can be developed. Have
them explain their reasoning. If a student suggests the number of electrons
moved is limited by the total number of electrons in the material, ask them
if there might be another phenomenon acting which may prevent the charge
difference between the two materials from becoming too great.
Ask the students to compare their answers with the reason given in the next
RESUME the video.
PAUSE the video at the point where the narrator asks "if you
are wearing a negatively charged shirt, how can you neutralize it?"
Ask the students to answer the question. You may need to have the students
count the positive and negative charges on the screen.
Ask the students to check their answers against the video segment. They
are also to listen for and to write a definition for grounding an object
in their worksheets.
RESUME the video.
PAUSE the video when "Grounding" is on the screen with
the ground symbol. Check for student comprehension of the definition.
the video for one second and pause once the man's arm is on the screen.
Ask the students to determine the charge on the man's arm and what they
expect the charge to become when his finger touches the pipe.
RESUME the video, instructing students to verify and correct their
answer based on the material presented.
PAUSE the video when the narrator asks "what happens if you
have a positive charge?" Have a student answer the question. Have the
students in the class write the answer. During the next segment have students
verify if the answer they gave was correct.
RESUME the video and
allow the video to continue through the explanation of an electroscope.
STOP the video after the description of an electroscope where the
narrator says "insulated by the container that encloses it." Explain
to the students that they are going to build their own electroscopes and
use them in connection with the video. (Use and distribute "Directions
for building an Electroscope.")
Once the students have completed the electroscopes, distribute to each pair
of students a glass rod, rubber rod, wool, and silk. Instruct the students
to rub the hard rubber rod with the wool. Explain that since the rubber
rod has a stronger affinity with electrons than does the wool, the rod develops
a negative charge. Once the rod has a charge instruct the students to touch
the rod to the knob of the electroscope and explain the reaction of the
electroscope on their worksheets.
Ask the students to describe in their worksheets the motion of the electron
between the rod and the electroscope as shown in the next segment on their
RESUME the video.
PAUSE the video where the narrator says "charging by contact"
and have the students write "charging by conduction" in their
notes, explaining it is synonymous. On the viewing activity worksheet have
the students mark down how they believe the charge will be distributed.
Ask the students to verify their answers against the next segment.
PAUSE the video at the point where a glass rod is first seen being
brought near the knob of the electroscope. Have the students discharge their
electroscopes by touching them. The students should now rub their glass
rods with silk and touch them to the knob of the electroscope. Explain to
students that the silk has a greater affinity with electrons than does the
glass. The students should determine the motion of electrons through the
electroscope and draw the charge distribution of the electroscope on their
Once the students have completed their diagrams, instruct them to verify
the charge distribution shown in their worksheets against the next segment.
Instruct the students to make any necessary corrections to their worksheets.
RESUME the video.
PAUSE the video at the point where the video shows the complete
charge distribution on the electroscope, allowing the students to make corrections.
Remove Electricity #2: Charging and Discharging from the VCR. Insert
Electricity #3: Charging by Induction, cued so it is at the point
where the narrator says, "Have you ever noticed that an electroscope,
when approached by a charged rod, seems to anticipate what is about to happen?"
Instruct the students to discharge their electroscopes, charge their glass
rods with the silk and bring their rods near the electroscopes without touching
the knob on the top of the electroscope. Have them to write down what they
notice in their worksheets and why they believe it happens. In the next
segment tell the students to write in their worksheet the reason given for
the reaction of the electroscope.
START the video.
PAUSE the video when the narrator says "as a result the leaves
repel themselves and diverge." Have the students copy the charge distribution
of the electroscope from the screen, after which they should calculate the
charge on the knob and the charge on the leaves of the device as well as
the total charge on the electroscope. The students should perform this calculation
by adding the number of positive charges and subtracting the number of negative
charges. Ask the students to verify their charge distributions against the
next video segment.
RESUME the video.
PAUSE the video when the video states "Induced separation of
charge." Instruct the students to copy this down and write a definition
from what they have just seen and heard. Ask the students what they believe
happens to the charge when the rod is removed. Tell the students to verify
their answers against the video if they were correct.
PAUSE the video once the charges have returned to their original
position and the leaves have collapsed. Instruct the students to rub the
glass rod. The charged rod is held near it and checked against their previous
answer. Start with the silk, recharging the rod, and hold it near the knob
of the electroscope without touching it. While holding the rod in this position,
tell the students to touch the knob of the electroscope with their fingers
and observe what happens to the device. The students should then remove
their fingers and then remove the rod. Once again, the students are to write
down their observations. On the worksheet, have the students write how a
charge travels through the ground and what the charge is in the electroscope.
RESUME the video. Instruct the students to list the three movements
of the electrons as the video reviews them. They are to label this section
"charging by induction."
Tell the students that they are going to perform a similar experiment
as to what they have just done, except that they are going to use a hard
rubber rod rather than glass. During each step of the procedure they are
to describe the motion of the electrons and the charge on the knob and leaves
of the electroscope. Have the students charge the hard rubber rod by rubbing
it with wool. Once the rod has developed a negative charge the students
should hold it near the knob of a completely discharge electroscope. Next,
the students should touch the knob of the electroscope, still holding the
rod near the knob. The students should remove their fingers from the device.
Finally, the students should pull the rod away from the device.
The electrostatic force between charged bodies can be calculated using a
relationship known as Coulomb's Law, F= kq1q2 /r2, where F is the force
of attraction or repulsion between the charged bodies in newtons, N, k is
the electrostatic constant, 9.0 x 109 Nm2/C2, q and q are the magnitude
and sign of the charges in coulombs, C, and r is the distance between the
centers of the charged bodies in meters, m. Using this relationship, have
the students determine what would happen to the force between the two charged
bodies if the distance between the bodies is doubled, tripled or divided
in half. Have the students graph the relationship between electrostatic
force and the distance between the bodies. Have the students determine what
would happen to the force between two charged bodies if the magnitude of
one or both of the charges is doubled, tripled, or halved.
Place the students into small groups to complete one of the
following projects. At the completion of the project the groups would be
responsible to present their findings to the class.
The students should take home the electroscopes they built. Knowing that
a hard rubber comb run their hair will acquire a negative static electric
charge, they are to devise a method using their electroscopes to determine
if statically charged objects, such as a person rubbing their feet on the
carpet, or the front of a television picture tube, have a net negative or
positive charge. They must be able to explain the motion of charge within
the electroscope and how they used this to determine the charge of these
Computers are susceptible to damage by electrostatic charges. Research why
they are so delicate and how designers have helped alleviate this problem.
We use current electricity in most of our everyday appliances. However,
the production of it is by a method different from that of static electricity.
Investigate this method.
Ben Franklin is considered a discoverer
of electricity. Investigate what were some of the early uses Franklin devised
for his discovery. George Westinghouse and Thomas Alva Edison promoted two
different types of electrical generation and distribution. Investigate what
were the two methods, what method was finally chosen, and why.
Most of our examples of static electricity involve the rubbing
of two solids together, however, lightning is a large static electric discharge
yet there are no two solids rubbing together. Investigate how lightning
is produced and describe the different types of lightning. The relationship
between two statically charged bodies is very similar to the relationship
between gravitationally attracted bodies. Investigate similarities and differences
between these two relationships.
Master Teachers:Ken Abbott and William Leacock
Lesson Plan Database
Thirteen Ed Online