Are You Suprised ? s79

Electrophorus: Lesson Plan

Introduction: The third electrostatic lab/activity uses the Electrophorus to reinforce charging by friction, charging by conduction, and polarization of charge and to introduce variations of charging by induction. Acknowledgments: This lab is built loosely around the Exploratorium’s Summer Institute’s – Electrophorus

Timing: This lab/activity should take about an hour and a half to complete (without building the electrophorus).

Group Size: Small groups

Learning Objectives: The objective of this lab/activity is to: a) Introduce the following key concepts: -Charging by Induction -Grounding b) Reinforce the following concepts from the previous lab work: -Charging by friction -Polarization of charge -Charging by conduction

Guiding Question: What are the techniques to electrically charge an object and how does the type of charge produced vary with each technique?

Materials: Each lab group should have three Electrophorus devices, two Styrofoam plates, two neon glow tubes. - Electrophorus devices are easy to build and a handout on constructing them has been attached to this lesson. Make sure to reinforce the tape connecting the insulating cup and the pie tin between classes. - Neon glow tubes are low power, high voltage lamps and can be found by doing an internet search or you can buy them from: http://www.surplussales.com/Bulbs-Incan- Panel/BulbsNeon.html. Buy either the Neon Lamp with Resistor115 vac or the Neon Lamp 90 vac. The resistor version is nice, but you need a bit more juice to fire the bulb, but you won’t blow as many.

Procedures: Electrophorus devices work best with low humidity, but still can have decent results with moderate humidity. Pick the experiment day accordingly. Having students build the Electrophorus devices the day before helps. The construction of the electrophorus devices should take no more than 15 minutes. Part 1: As students follow the procedure on the lab sheet, the instructor should make sure students: - are not accidentally grounding the Electrophorus by touching the pie tin. - are only touching one connector of the neon bulb to the Electrophorus.

Part 2: As students follow the procedure on the lab sheet, the instructor should make sure students are following the Part 1 precautions.

Part 3: As students follow the procedure on the lab sheet, the instructor should make sure students are following the Part 1 precautions and: - are touching the uncharged Electrophorus at the farthest point away from the charged Electrophorus.

Part 4: As students follow the procedure on the lab sheet, the instructor should make sure students are following the Part 1 precautions and: - are very careful not to ground either of uncharged Electrophori when separating them.

Part 5: As students follow the procedure on the lab sheet, the instructor should make sure students are following the Part 1 precautions and: - put their finger on the far side of the uncharged Electrophorus. - only place their finger on and remove their finger from the uncharged Electrophorus while the charged Electrophorus is near, but not in contact.

Assessment: Throughout the first 5 sections of the experiment, students will complete questions and charge distribution diagrams based on their experiences and gained knowledge. The instructor should correct any inaccuracies in student answers and diagrams during the actual experiments. Since the answers and diagrams have already been checked, these should be graded for completion. The last section is a 10-question assessment of the lab experiences and gained knowledge. These should be graded for correctness.

Answer Key: Part 1 Closure: 1. Did you feel any forces between the electrophorus and the foam plate? The plate wants to stick to the pie tin, so yes.

2. Was the electrophorus charged? How did this happen? Discuss electron transfer in your explanation. Yes, the electrons were ripped away from the Electrophorus (pie tin) by the Styrofoam plate.

3. The Styrofoam plate is an electron taker, which means it strips electrons from the electrophorus when they are rubbed together. After charging the electrophorus, what are the net charges on each? The plate is negatively charge, while the Electrophorus is positively charged.

Part 2 Closure: 1. Why is conduction called charging by contact? Objects actually come in physical contact with each other and electrons are transferred from the charged object to the uncharged object, giving them the same overall charge.

2. Assuming that a charged electrophorus has a net positive charge, sketch the charge pattern that was produced when the two were in contact.

Part 3 Closure: 1. Was the electrophorus polarized? How did this happen? Yes, when the positively charged Electrophorus is brought near but not in contact with the uncharged Electrophorus its charge is split. The negative charges are attracted to and the positive charges are repelled from the positively charge Electrophorus. Even though the charge is split, the overall net charge is neutral.

2. Assuming that a charged electrophorus has a net positive charge, sketch the charge pattern that was produced in the diagram above.

- - + + - + + - + + - - - + +

Part 4 Closure: 1. Did the neon bulb light up for either of the uncharged electrophorus? Should light up for both.

2. Assuming that a charged electrophorus has a net positive charge, sketch the charge pattern that was produced in the diagram above. Step 1 Step 2 Step 3 Step 4

  + - + + - + - +

3. What types of charge did you produce in each electrophorus? How do they relate to each other? You should produce unlike charge (negative) in the near uncharged Electrophorus and like charge (positive) in the far uncharged Electrophorus. They are opposites of each other. 4. Which charge (positive or negative) seems to produce more light from the neon bulbs? Positive seems to light up better, but it is not always the case.

Part 5 Closure: 1. What was the purpose of touching the uncharged electrophorus on the far side? Hint: Think polarization of charge and what type of charge will to get away from the positively charged electrophorus. Touching the Electrophorus allows the like charge (positive) to be repelled from the positively charged Electrophorus to the ground.

2. Why would the finger touching the electrophorus be considered “grounding”? Your finger is connected to you, which is connected to your feet, which are connected to the ground. The charge will flow through the body to get to the source of infinite charge, the ground.

3. Assuming that a charged electrophorus has a net positive charge, sketch the charge pattern that was produced in the diagram above. Step 1 Step 2 Step 3 Step 4

+ - + + - + + - - 

4. What are the main differences between the two types of induction? The first type of induction will produce unlike and like charges to the charged Electrophorus, while the second type of induction only produces the unlike charge.

Individual Closure: 1. b. Friction

2. b. the same.

3. d. Answers (a) and (c)

4. c. neutral.

5. c. Induction

6. b. Negative

7. Charge flows due to a difference in charge. True

8. b. the ground. 9. a. The two objects can be separated and one will be positive and other negative.

10. b. Negative