# Static Electricity

P.49-50 AQA GCSE Physics Revision Guide

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• Created by: jenny100
• Created on: 25-05-12 10:20

## 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
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## 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.

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## Static Electricity - Examples

Smoke Precipitators:

• 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

Photocopier:

• 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
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## Comments

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I Like how this is just the CGP revision guide :)

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