012–07227A
Basic Electrostatics System
11
6. Push the zero button to remove any residual charge. Now insert the object
again, but let it touch the ice pail. Make sure your students know and see that
you are touching the ice pail with the charged disk this time.
7. Remove the object and note the electrometer reading.
Questions: Why is there now a permanent potential difference between the ice
pail and the shield? Where did the charge on the ice pail come from?
8. To show that the charge gained by the ice pail was lost by the disk, ground the
ice pail to remove all charge. Press the ZERO button to remove residual charges
from the electrometer. Insert the wand again into the ice pail. Does any charge
remain on it?
Procedure 1B: Conservation of Charge
1. Starting with initially uncharged charge producers, rub the blue and white
materials together. Follow the general procedure for charging listed in part A,
except that in this case you must keep both producers from touching anything
else after charging. (Keep them in your hands, without letting them touch each
other or the ice pail.)
2. Use the Faraday Ice Pail to measure the magnitude and polarity of each of the
charged wands by inserting them one at a time into the ice pail and noting the
reading on the electrometer.
Questions: What is the relation between the magnitude of the charges?
What is the relation between the polarity of the charges?
Was charge conserved in the demonstration?
3. Completely remove all charge from the charge producers by grounding them.
Do not forget to also remove any stray charge from the necks and handles.
4. Insert both charge producers into the ice pail and rub them together inside the
pail. Note the electrometer reading. Do not let the charge producers touch the pail.
5. Remove one charge producer and note the electrometer reading. Replace the
charge producer and remove the other. Note the electrometer readings. Using
the magnitude and polarity of the measurements, comment on conservation of
charge.
Extra Things to Try
1. Try repeating Procedure A with the opposite charged wand.
2. Try rubbing the white charge producer with a proof plane, then measure the
magnitude and polarity of the charges produced.