When two insulating materials are rubbed together, electrons are scraped off of one and dumped onto the other.
This leaves a positive static charge on one and a negative static charge on another.
The way in which electrons are transfered depends on the two materials involved:
Polythene Rod and Duster: The negative electrons move from the duster to the rod.
Acetate Rod and Duster: The negative electrons move from the rod to the duster.
Electrically charged objects attract small objects placed near them.
Both positive and negative electrostatic charges are only ever produced by the movement of electrons.
Positive charges definitely do not move. A positive charge is caused by the electrons moving.
A charged conductor can be discharged safely by connecting it to earth by using a metal strap. The electrons flow to the ground if charge is negative and flow up if the charge is positive.
Like charges repel, opposite charges attract.
The greater the charge on an isolated object, the greater the potential difference between it and earth. If the potential difference gets big enough then a spark jumps across the gap.
Examples of Static Electricity
The Smoke Precipitators:
- As smoke particles reach bottom of chimney, they meet a wire grid with a high negative charge. This negatively charges the smoke.
- The negatively charged smoke is attracted to positively charged metal plates. The smoke particles stick together to make larger particles.
- The particles then fall off or are knocked off by a hammer.
- The image plate is positively charged. Your image is projected onto them.
- Light bits of the thing you are copying make light fall on the plate, making the charge leak away from those areas.
- The charged bits attract negatively charged black powder, which is transfered onto positively charged paper.
- The paper is heated so the powder sticks, a photocopy is made.