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Jan Dudzik Riverside Brookfield High School
1st and Ridgewood
Riverside IL 60546
High school students will identify two types of charges and will observe
the charging of with various objects by friction, conduction, and induction.
For each group: Magic tape, golf tube, cat fur, wool, electrophorus, salt,
pepper, cereal, slates and markers.
For teacher use: Van de Graff generator, spectral tube, mini electrostatic
precipitator (made from plastic 2 liter bottle with two bands of aluminum
foil and pins with paper clip leads to connect to Van de Graff).
Part 1: Give each group tape. Tell them to tear off two pieces about the same
length. Have students stick the tape to the table side by side, rub them and
then pull them off quickly. Tell students to record what happens when they
bring the two pieces of tape close together and encourage them to experiment
with the tape trying various pulling speeds, lengths and thicknesses and record
their findings on the white boards with markers. Bring one member of each group
to the front of the class and share results. The class should arrive at a
consensus that there are two distinct charges and that rubbing the tape apart
produces a charge that repels and rubbing tapes on top of each other produces a
charge that attracts. Next, hand out to students the golf tubes and wool cloth
and tell them to charge the tubes using friction. Get them up, out of their
seats and tell them to find a favorite attractive object in the room to share
with the class. (Have various materials in the room: cereal, salt, pepper,
balloons, etc.) When students find their object tell them to sit down. Call
them down and have them share their findings with the rest of the class.
Reemphasize to the class the fact that and object can be charged by friction and
can attract objects.
Part 2: Ask students if they think that they can get heavy things to move with a
charged tube. Have them check their neighbor and vote on their white boards.
Post the tally. Then, charge a golf tube and bring near a 2 x 4 board balancing
on a spoon. When it moves and students are mystified, inform them how strong
electrical forces are compared to gravitational forces. Ask students to find
out if electrical forces are strong enough to snap charges from neutral objects.
Give each group an electrophorus and tell them to charge the bottom plastic
plate and then place the neutral pan on top of it. Have them pick up the
neutral pan by the handle and bring it near an object to see if it is charged.
Note student observations and then instruct students to repeat only this time
have them touch the pan with their finger before lifting. A charge should snap
off and be heard and felt. Ask if the pan was charged in the first case and
then ask if it was in the second case. Students should realize that touching
the pan helped the pan to become charged. Illustrate the process of induction
on the board. Then, call upon two student volunteers to illustrate this one
more time in front of the class. Shut the lights off and hand one of the
volunteers a spectral tube. When the charged plate touches it, it should glow.
Mention that this glow is seen because the tube has molecules of gas that are
easier to excite than air molecules. Then, bring the volunteers over to the Van
de Graff generator and ask one to stand with one hand on the top of the
generator and hold the other student's hand. Turn on generator and charge
students. Have another one come up and join the chain. Illustrate the
difference between charging by conduction, induction, and charging by friction.
Show students the 2 liter bottle electrostatic precipitator. Point out the
features of design. Burn the incense and turn on the precipitator. Ask
students to explain how the smoke is trapped by the precipitator.