http://www.ck12.org Chapter 15. Electrostatics
FIGURE 15.10
Grounding Disk B.FIGURE 15.11
Removal of grounding wire ensures Disk
B is positively charged.- Why is it that only the negative charges move?
Answer: Positively charged ions may also move (in gases or liquids, for example) but not in solid objects. When
we speak of a positively charged object, the object has lost electrons and has become positively charged. It has not
experienced an actual transfer of positive ions.
There is a fourth state of matter called plasma, which is a highly ionized gas typically formed at high temperatures
and consisting of freely moving ions and electrons. The sun’s “solar wind” is an example of plasma which interacts
with the earth’s atmosphere. The plasma from the sun is responsible for ionizing the upper atmosphere of the earth,
contributing to the plasma found in the earth’s radiation belts.
Charge on Metallic Conductors
It has been shown experimentally that any excess electrons on a metal conductor will migrate to the outside surface
of the conductor. For example, if electrons are deposited inside an open tin can, the electrons will migrate to the
outside of the can. No free electrons will remain inside the can.
This is very useful information. It means we would be safe from an electrical discharge (such as lightning) inside of
a “metal cage” since all the charge is conducted to the outside of the metal cage. So, stay inside your car during a
lightning storm! Electronic components are protected also from electrical discharges by enclosing them inside metal
containers.