If electrons are removed from one material and placed on another, or if they are moved from one region of a piece of material to another, we have a separation of charge. The material, or area, that receives the electrons becomes negatively charged and the material or region that loses electrons becomes positively charged. If these accumulations of charge remain stationary after their transfer, they are referred to as static electricity.
Common examples of static electricity are the small shock you get when you touch a door handle having walked across a carpet, or the crackling you hear when you remove certain items of clothing. In both cases electrons have moved from one material to the other. This type of static charging between two or more dissimilar materials is known as triboelectric charging and is a very important factor in the design of aircraft and aircraft furnishings and equipment.
The nature and size of the charge produced depends on the materials, some loose or gain electrons more easily than others. The Triboelectric series on the next page list materials in the order in which they gain or loose electrons. The list is arranged such that, if any two materials are selected and rubbed together the one higher up the list will obtain a positive charge and the one lower down the list, a negative charge. So if a glass rod is rubbed with fur, the rod will become negatively charged, but if it is rubbed with nylon it will become positively charged.
When an insulating material is charged by rubbing it with another material, the electrons are not free to move through the material. The charge therefore remains at the point of friction. If a conductor is charged through rubbing, the electrons are free to move and the charge will dissipate unless the conducting material is insulated from its surroundings.
If two statically charged items are brought into contact with one another, electrons will transfer from the more negative to the more positive one. This movement of electrons constitutes a current flow, which will cease once the charges are equal.
The region around the charged body may be detected and is called an electric field, the electric field is analogous to a magnetic field, which will be studied later in the course. The electric field is represented in magnitude and direction by electric lines of force. The density or magnitude of the force may be represented by the number of lines, and the direction is indicated by arrows that point from positive to negative.