Triboelectric Effect
Objectives
- Study how charge moves in conducting material
- Construct a triboelectric series chart for different objects based on their static electrical charging characteristics
Resources
- Aluminum can electroscope
- friction rods, silk, animal fur, etc.
Background
The triboelectric effect is a type of contact electrification on which certain materials become electrically charged when they are rubbed against other materials. Rubbing glass with fur for example, or a plastic comb through the hair, can build up excess charge of opposite sign on both objects. Most everyday static electricity is triboelectric. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, and other properties.
A triboelectric series lists materials in order of the polarity of charge separation when they are touched with another object. A material towards the bottom of the series, when touched to a material near the top of the series, will acquire a more negative charge. The farther away two materials are from each other on the series, the greater the charge transferred. Interestingly, the actual sign of charge – i.e. positive or negative – cannot be determined by rubbing two objects – the assignment of (+) or (-) is arbitrary.
You will use an electroscope in this lab to detect the presence of excess charge in objects. The electroscope is an electrically insulated aluminum can with small foil strips hanging from a copper wire attached to one end. Objects with a surplus electrostatic charge that are brought near the body of the electroscope will cause excess charge in the electroscope of the same sign to move into the foil strips, making them repel each other and spread apart. Touching the object to the electroscope body will allow charge to spread evenly between the object and electroscope, causing the electroscope to become charged with whatever excess charge existed in the object. Your body is a large reservoir of charge, so the electroscope can be returned to neutral (grounded) by simply touching it with your hand.