Category Archives: Electric Fields and Potential

Wimshurts/Ping-Pong Demo

Demo: EM-B-WP

Pira Index: 5B 10.35


  1.  Wimshurst machine (large)
  2. Ping-pong pie pan set
  3. 2 short A-A leads
  4. Plexiglas box
Option: Ping-pong popper can be set on top of Van de Graaff instead of using the Wimshurst.
  1.  Setup as shown. Move the Wimshurst discharge arms outward away from each other as shown.
  2. Place the ping-pong set on top of the plexiglas box to isolate it from ground.
  3. Be sure that the A-A leads are isolated from each other and from ground. Attach one to top pan and other to the bottom pan.
  4. Crank Wimshurst machine. As you gain speed and charge the ball will bounce rapidly up and down.

Caution: to discharge the Wimshurst, carefully swing the discharge arms to the middle of the apparatus until they touch.

Wimshurst and Flame

Demo: EM-B-WF

Pira Index: 5B 30.40


  1.  Wimshurst machine
  2. Modified sliding capacitor
  3. Candle with PVC holder and matches
  4. 2 copper rods
  5. Plexigas box (or stacks of licorice containers)
  1. Set up as shown with discharge arms separated and copper wires hooked to each of them and to attachment screws on the sliding capacitor.
  2. Light candle.
  3. Charge up the device by cranking (has to be turned relatively fast to build a charge).
  4. Since the gases producing the candle flame are ionized (having lost electrons) the positively charged gases of the flame will be attracted by the negative plate.

Caution: to discharge the Wimshurst, carefully swing the discharge arms to the middle of the apparatus until they touch.

Van de Graaff

Demo: EM-B-VG

Pira Index: 5B 10.10


  1.  Van de Graaf generator
  2. Insulated platform
  3. Plastic box containing:   Electrostatic plume, electric popcorn, electric whirl, pie tins, wand with foil ball
  4. Sphere on a stand
  5. Tin can (Hersheys) with styrofoam
  6. Large plastic beaker
  7. Fluorescent tube (stored in foam “bag”)
  8. Neon spectral tube
  1.  Have student stand on platform and place hand on top of Van de Graaff. Do not remove hand from the surface.
  2. Turn on Van de Graaff and observe the student’s hair.
  3. Turn off Van de Graaff, use grounding wire (attached to base of generator) to discharge sphere, and allow student to withdraw hand.
  4. Place each equipment item (3-5), one at a time, on top of the Van de Graaff and turn it on. Use the metal-tipped lead attached to the bottom of the Van de Graaff to discharge it each time before touching.

Transferring Charge

Demo: EM-B-TC
Pira Index: 5B 20.10

  1.  PVC electrophorus
  2. Paper towel
  3. Electroscope with pail (can) atop it
  4. Charge transferring ball
  1.  Charge the Ice Pail (can) with the electrophorus. (see hand-out card for instructions)
  2. Alternately touch the transferring ball to the inside of the pail and then to your hand. After several repetitions, observe that nothing happens.
  3. Repeat the transferring process, this time touching the ball to the outside of the pail. Notice the drain of charge (the electroscope leaf falls).
  4. OPTION: Charge ball by induction (see hand-out card) and hold it in the center of the pail.

Since the ball is charge oppositely from the pail, the electroscope shows more charge.



Radio in a Cage

Demo: EM-B-RC
Pira Index: 5B 20.35

  1. Transistor radio taped to a pie pan
  2. Faraday cage
  3. Pie pan
  4. Special 7W bulb light source
  1.  Turn on the light and the radio (do not have the Faraday cage over the radio at this point).
  2. You should hear static which the radio picks up from the fluorescent light source.
  3. Place the Faraday cage over the radio (pie pan on top) and you hear nothing.


Popcorn Popper

Demo: EM-B-PP
Pira Index: 5B 10.30

  1.  Popcorn popper
  2. PVC plate (gray plate)
  3. Rabbit fur
  1.  Rub the fur back and forth against the PVC until it acquires a charge.
  2. Place the metal pan with the Styrofoam handle on the plate; touch the edge of the pan with your finger.
  3. Pick up the plate by the Styrofoam handle and place it on top of the popper.
  4. Repeat step 2 and 3 several times. The “popcorn” should then begin popping.

Option – Popper can be set on top of Van de Graaff instead of using the charging box.


Electric Field Tank

Demo: EM-B-FT
Pira Index: 5B 10.40

  1.  Large square tank with set of weight hangers, rods, and leads
  2. Bag of model railroad flock
  3. Shell dielectric oil
  4. Dirod static generator
  5. Overhead projector
  1.  Put the tank on the OHP and pour 1/4″ of oil into the bottom of the tank.
  2. Connect the dirod to a pair of electrodes: weight hangers (point-point), 2 rods (plane-plane), or some other combination. Place the electrodes into the tank. Sprinkle flocking into the oil and stir to disperse somewhat evenly.
  3. Crank the dirod and watch the flocking line up in a pattern typical to the electrodes used.
  4. Stop charging and give it time to equalize before trying another pair.


Faraday Cage

Demo: EM-B-FC
Pira Index: 5B 20.30

  1.  Faraday cage and charge producer rods
  2. Pasco electrometer
  3. Special cable for electrometer
  4. Shortened cord with plug
  5. Galvanometer
  6. BA lead, 2 BB leads
  1.  Set up as shown.
  2. Rub the blue and white charge producers together. Insert one of them into the inner pail and observe the meter. Repeat with the other charge producer.
  3. Ground the charge producers and rub the white probe with the aluminum proof plane. Observe the magnitude and polarity of the charges. Repeat with the blue probe.


E-Field Density

Demo: EM-B-ED
Pira Index: 5B 30.30

  1.  Pasco Van de Graaff
  2. Point and sphere assembly with strings
  3. 1/2″ PVC pipe for vertical support
  4. Telescope clamp and wood block
  1.  By hand cranking the Van de Graaff, charge the sphere and point assembly.
  2. When you stop charging, the charge quickly begins to drain off through the string attached to the Van de Graaff. Note which the point strings or the sphere strings retain charge by watching the collapsing of the strings attached to each. (The sphere with its large radius loses charge more rapidly than the point).