UW PHYSICS DEMONSTRATION CATALOG

	UW-Madison Physics Demonstrations Using the PIRA Scheme
	What would you like to see in an on-line demonstration catalog? This is a test catalog of a portion of the Department's electrostatics demonstrations--heading 5A of the PIRA scheme. Please look over the descriptions below and send comments on the format to Jim Reardon. First draft 1 April 2008.

5A00.00 Flamingo and Bag

Rub flamingo with bag; flamingo charges negative.

That flamingo is charged can be proved by bringing it near an electroscope.

This demonstration is used to show that even everyday objects (that is, objects of a type not found solely in physics class) can be charged.

5A10.20 Electrophorus

Electrophorus = "charge-bearer".
Place flat acrylic plate on grounded conducting plane (not shown).
Rub plate with fur to charge it negative.
Place electrophorus on plate, momentarily ground top surface of electrophorus.

Remove electrophorus. Potential of electrophorus may be as high as 30 kV.
More info:

http://www.ece.rochester.edu/~jones/demos/electrophorus.html

5A20.10 Stirrup

Rub clear rod with cat fur. Clear rod charges positive. Place it in stirrup (which hangs from non-conducting silk thread) as shown.

Rub black rod with cat fur. Black rod charges negative.

Hold black rod near clear rod. The two rods attract.

5A20.20 Two pith balls

Rub rod with cat fur to charge rod.

Bring rod near two pith balls (pith balls hang from insulating thread).

At first balls are attracted to rod.

When they touch, charge transfers. Now they are repelled by rod, and by each other.

Pith Ball Pitfalls:

Pith balls act as imperfectly conducting spheres. Charge on the surface may or may not be free to move. Induction effects may be important to pith ball dynamics.

Cylinder and balls, 5A20.23

Rub rod with cat fur and touch rod to cylinder.

Electric field around cylinder approximates field due to finite line charge on cylinder axis.

Pith balls show presence of electric field surrounding charged conductor.

5A22.10 Electrometer

Rub rod with fur, touch rod to knob on top of electrometer. Full-scale needle deflection 1500V (easy to achieve with rod and fur).

5A22.10 Electroscope

Rub rod with fur, touch rod to knob on top of electroscope, leaves diverge indicating non-zero charge on electroscope.

Rub same rod with fur, bring it near but not touching knob. Leaves diverge further.

Rub the other rod with the fur, and bring it near but not touching. Leaves droop.

This indicates there are two types of charge, and that that which attracts one repels the other.

5A40.40 Water Stream

Fill sawed-off milk carton with water and add several drops of green food coloring to make water more visible.

Open valve to let a stream of water run out (into catch basin).

Rub rod with fur and bring it near stream of water.

Stream of water attracted toward the rod (see picture).

5A50.10 Wimshurst generator

Turn crank on Wimshurst generator (crank cannot be seen; it is on reverse side of disk) so that disk spins.

Brushes which contact the spinning disk are connected to electrodes (small silver balls in top center) in such a way that small asymmetries in charge on electrodes are amplified.

1" spark can easily be drawn, indicating potential difference of about 30kV between electrodes.

5A50.15 Toepler-Holtz generator

Turn crank on Toepler Holtz generator.

It is similar to Wimshurst generator in that brushes which contact spinning disk are connected to electrodes in such a way that small asymmetries of charge on electrodes are amplified.

It differs from Wimshurst in that electrodes are connected to Leyden jars so that spark, when it occurs, carries a larger current.

SAFETY: The spark from a Toepler-Holst can be painful and cause injury. Do not touch or put body parts close to the electrodes until you are sure they are grounded. To ground the electrodes, put one hand in your pocket and use the other hand to grasp one of the insulating handles on the ends of the electrodes to bring them together.

5A50.30 Van de Graaff Generator

God's gift to physics outreach. Turn on power; big silver electrode charges positive (true for the current model, from Cenco; this depends on materials used for belt and rollers).

When working well spark jumps to small electrode, indicating potential difference of about 100kV, every 0.5 seconds or so.

Wooden rod with nail on end is connected to ground and can be used to remove charge.

With machine off:

Remove small electrode, and ask volunteer to stand on plastic stool and place hand on large electrode.

Turn machine on.

Volunteeer's hair should stand up straight.

Ground large electrode.

Turn off machine.

Note: The spark from this machine can sting but injury is unlikely because the capacitance of the big silver electrode is not that large.

5A00.00 Flamingo and Bag Rub flamingo with bag; flamingo charges negative. That flamingo is charged can be proved by bringing it near an electroscope. This demonstration is used to show that even everyday objects (that is, objects of a type not found solely in physics class) can be charged.
5A10.20 Electrophorus Electrophorus = "charge-bearer". Place flat acrylic plate on grounded conducting plane (not shown). Rub plate with fur to charge it negative. Place electrophorus on plate, momentarily ground top surface of electrophorus. Remove electrophorus. Potential of electrophorus may be as high as 30 kV. More info: http://www.ece.rochester.edu/~jones/demos/electrophorus.html
5A20.10 Stirrup Rub clear rod with cat fur. Clear rod charges positive. Place it in stirrup (which hangs from non-conducting silk thread) as shown. Rub black rod with cat fur. Black rod charges negative. Hold black rod near clear rod. The two rods attract.
5A20.20 Two pith balls Rub rod with cat fur to charge rod. Bring rod near two pith balls (pith balls hang from insulating thread). At first balls are attracted to rod. When they touch, charge transfers. Now they are repelled by rod, and by each other. Pith Ball Pitfalls: Pith balls act as imperfectly conducting spheres. Charge on the surface may or may not be free to move. Induction effects may be important to pith ball dynamics.
Cylinder and balls, 5A20.23 Rub rod with cat fur and touch rod to cylinder. Electric field around cylinder approximates field due to finite line charge on cylinder axis. Pith balls show presence of electric field surrounding charged conductor.
5A22.10 Electrometer Rub rod with fur, touch rod to knob on top of electrometer. Full-scale needle deflection 1500V (easy to achieve with rod and fur).
5A22.10 Electroscope Rub rod with fur, touch rod to knob on top of electroscope, leaves diverge indicating non-zero charge on electroscope. Rub same rod with fur, bring it near but not touching knob. Leaves diverge further. Rub the other rod with the fur, and bring it near but not touching. Leaves droop. This indicates there are two types of charge, and that that which attracts one repels the other.
5A40.40 Water Stream Fill sawed-off milk carton with water and add several drops of green food coloring to make water more visible. Open valve to let a stream of water run out (into catch basin). Rub rod with fur and bring it near stream of water. Stream of water attracted toward the rod (see picture).
5A50.10 Wimshurst generator Turn crank on Wimshurst generator (crank cannot be seen; it is on reverse side of disk) so that disk spins. Brushes which contact the spinning disk are connected to electrodes (small silver balls in top center) in such a way that small asymmetries in charge on electrodes are amplified. 1" spark can easily be drawn, indicating potential difference of about 30kV between electrodes.
5A50.15 Toepler-Holtz generator Turn crank on Toepler Holtz generator. It is similar to Wimshurst generator in that brushes which contact spinning disk are connected to electrodes in such a way that small asymmetries of charge on electrodes are amplified. It differs from Wimshurst in that electrodes are connected to Leyden jars so that spark, when it occurs, carries a larger current. SAFETY: The spark from a Toepler-Holst can be painful and cause injury. Do not touch or put body parts close to the electrodes until you are sure they are grounded. To ground the electrodes, put one hand in your pocket and use the other hand to grasp one of the insulating handles on the ends of the electrodes to bring them together.
5A50.30 Van de Graaff Generator God's gift to physics outreach. Turn on power; big silver electrode charges positive (true for the current model, from Cenco; this depends on materials used for belt and rollers). When working well spark jumps to small electrode, indicating potential difference of about 100kV, every 0.5 seconds or so. Wooden rod with nail on end is connected to ground and can be used to remove charge. With machine off: Remove small electrode, and ask volunteer to stand on plastic stool and place hand on large electrode. Turn machine on. Volunteeer's hair should stand up straight. Ground large electrode. Turn off machine. Note: The spark from this machine can sting but injury is unlikely because the capacitance of the big silver electrode is not that large.

UW-Madison

Physics Demonstrations

Using the

PIRA Scheme