A STUDENT-MADE ELECTROPHORUS
Materials:









Aluminum pie pan
Styrofoam cup bendable straw
String
Aluminum straw (pith ball)
Tape
Styrofoam plate
Build the electrophorus as shown
Wax paper
Audiotape (1-2”)
Procedure:
1. Build the ELECTROPHORUS as shown. Cut a slice in the straw so a
string can slide up and down it to adjust the foil balls height.
2. The foil ball should be level with the edge of the pan but about ½”
away.
3. Rub the Styrofoam sheet briskly and lightly with the piece of Wax
paper. This causes electrons from the Wax paper to be rubbed off
onto the surface of the Styrofoam sheet. Place the pie pan on the
Styrofoam sheet, and touch the lip of the pie pan with your fingertip.
What do you observe? ___________________________________
4. Now, using the Styrofoam cup handle, lift the pit pan from the
Styrofoam sheet and hold your finger close to the foil ball.
5. What do you observe now? _______________________________
Based upon your observations in this activity, try to answer the following
questions:
6. Why do you think it is important to handle the pie pan by the
Styrofoam cup handle? ___________________________________
____________________________________________________
7. What do you think happened to the pie pan when it was placed on the
negatively charged surface of the Styrofoam sheet?
____________________________________________________
8. When you repeated the activity in Step 4, you did not have to rub the
wool across the Styrofoam sheet again. Can you infer why?
____________________________________________________
____________________________________________________
9. Why do you think the foil ball eventually slows and stops moving back
and forth. ____________________________________________
A STUDENT-MADE ELECTROPHORUS
Materials:









Aluminum pie pan
Styrofoam cup bendable straw
String
Aluminum straw (pith ball)
Tape
Styrofoam plate
Build the electrophorus as shown
Wax paper
Audiotape (1-2”)
Procedure:
1. Build the ELECTROPHORUS as shown. Cut a slice in the straw so a
string can slide up and down it to adjust the foil balls height.
2. The foil ball should be level with the edge of the pan but about ½”
away.
3. Rub the Styrofoam sheet briskly and lightly with the piece of Wax
paper. This causes electrons from the Wax paper to be rubbed off
onto the surface of the Styrofoam sheet. Place the pie pan on the
Styrofoam sheet, and touch the lip of the pie pan with your fingertip.
What do you observe? ___________________________________
4. Now, using the Styrofoam cup handle, lift the pit pan from the
Styrofoam sheet and hold your finger close to the foil ball.
5. What do you observe now? _______________________________
Based upon your observations in this activity, try to answer the following
questions:
6. Why do you think it is important to handle the pie pan by the
Styrofoam cup handle? Styrofoam is an insulator, it cannot conduct
electrical charges
7. What do you think happened to the pie pan when it was placed on the
negatively charged surface of the Styrofoam sheet?
When the pie pan is placed on the negatively charged styrofoam
sheet, there is a separation of charges induced in the pie pan. The
bottom side of the pan which is in contact with the sheet becomes
positively charged and the top surface of the pie pan becomes
negatively charged, though the net charge on the pie pan is still zero
8. When you repeated the activity in Step 4, you did not have to rub the
wool across the Wax Paper again. Can you infer why?
The fact that the activity can be repeated again without having to
first rub the wool over the styrofoam sheet again indicates that the
sheet still has a negative charge. In fact, no electrons from the sheet
were ever removed to the pie pan. Because styrofoam is an insulator,
molecules on the surface that have an extra electron are unable to
move the electrons to their neighbors or to surrounding materials.
9. Why do you think the foil ball eventually slows and stops moving back
and forth. ____________________________________________