Static Electricity - The Basics
Static electricity is about charges that cannot move meaning they build up in one place and this often ends in a spark or shock when they finally move
- Build-up of static is caused by friction:
- When two insulating materials are rubbed together electrons are scrapped of one and transferred to the other
- This leaves a positive charge on one and a negative on the other
- Which way the electrons are transferred depends on the 2 materials involved
- Electrically charged objects attract smaller objects placed near them
- Classic examples: polythene and acetate rods being rubbed with a cloth duster
- With the polythene rod electrons move from the duster to the rod
- With the acetate rod the electrons move from the rod to the duster
Static Electricity - The Basics 2
- Only electrons move - never the positive charges:
Both positive and negative charges are only ever produced by the movement of electrons, the positive charges do not move.
A positive static charge is always caused by electrons moving away.
A charged conductor can be discharged safely by connecting it to the earth with a metal strap. The electrons flow down the strap to the ground if the charge is negative and flow up the strap from the ground if the charge is positive.
- Like charges repel, opposite charges attract
- As charge builds up so does the voltage - causing sparks:
The greater the charge on an isolated object, the greater the voltage between it and the Earth. If the voltage gets big enough there's a spark which jumps across the gap.
Static Electricity - Examples
- As smoke particles reach the bottom of the chimney they meet a wire grid with a high negative charge, this charges the smoke negatively
- The charged smoke particles are attracted to the positively charged metal plates. The smoke particles stick together to form larger particles.
- When heavy enough the particles fall off the plates or are knocked off by a hammer. The dust falls to the bottom of the chimney and can be removed
- The gases coming out of the chimney have very little smoke in them
- The image plate is positively charged. An image of what your copying is projected onto it
- Whiter bits of the thing your copying make light fall on the plate and the charge leaks away in those places
- The charged bits attract negatively charged black powder which is transferred onto the positively charged paper
- The paper is heated so the powder sticks