Electrostatics

Jan Dudzik                     Riverside Brookfield High School
                               1st and Ridgewood
                               Riverside IL 60546
                               (708) 442-7500

Objective:

High school students will identify two types of charges and will observe 
the charging of with various objects by friction, conduction, and induction.

Materials:

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).

Strategy:

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. 

Assessment:

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.