"Project-O-Scope" Electroscope

Jane Pafundi

"Project-O-Scope" Electroscope Materials

A device used to measure electrostatic charges.

Description of Equipment

Electroscope

A. Transparent piece B. Torsion style needle

of plexi-galss

C. An aluminum electrostatic shield

D. Charging and grounding plate

Principles illustrated

Demonstrates the principles of electrostatics.

Producing a negative charge:

1. Ground the "Project-O-Scope" by touching the contact plate with your hand.

2. Rub an ebonite rod with wool.

3. Slide the rod slowly across the charging plate.

4. The "Project-O-Scope" now has a negative charge.

This occurs due to the negative electrons transferred from the wool to the rod and then to the contact plate. Since the "Project-O-Scope" started with equal amounts of protons and electrons it had no charge. After the rod was touched to the contact plate the electrons from the rod repelled the electrons in the plate into the electroscope producing a negatively charged electroscope.

Producing a positive charge:

1. Ground the "Project-O-Scope" by touching the contact plate with your hand.

2. Rub an acrylic rod with fur.

3. Slide the rod slowly across the charging plate.

4. The "Project-O-Scope" now has a positive charge.

This occurs due to the positively charged rod attracting the negatively charged electrons from the contact plate producing a positively charged electroscope.

Testing an Unknown Charge:

1. Charge the electroscope negatively as explained above.

2. Bring the unknown charge near the charging plate.

If the needle's deflection increases the unknown charge is a negative charge.

This shows there is an additional negative charge by adding to the needle's deflection.

If the needle's deflection decreases the unknown charge is a positive charge.

This shows there is a positive charge by reducing the deflection or taking away some of the negative charge.

Triboelectric Series:

The following is a Triboelectric Series for many household items. The further away items are on the list the easier it is to produce a charge when they come into contact with each other and then are separated. Positive items in the series are at the top, and negative items are at the bottom:

From: http://en.wikipedia.org/wiki/Triboelectric_effect