Static Electricity (Oxford AQA IGCSE Physics)

Static Electricity

• Static electricity is caused by a build up of electrons on the surface of an insulating material

• The charge is static or stationary because the electrons have no where to go such as through a conducting material

• This results in the repulsion of oppositely charged objects

• When a conducting route is provided the electrons can discharge by producing a spark

Generating static electricity

• All objects are initially electrically neutral

  • They have even numbers of positive and negative charges

• Rubbing two surfaces together transfers electrons from one object to the other

  • The object that has gained negative electrons becomes negatively charged

  • The object that loses negative electrons becomes positively charged

• Remember that:

  • Protons are the positive charges in an atom's nucleus so they cannot be transferred

  • Whether a material gains or loses electrons during rubbing depends upon its properties

• When an uncharged cloth is rubbed against an uncharged polythene rod

  • Electrons are transferred away from the cloth to the rod

    • The cloth has lost electrons so it becomes positively charged

    • The polythene rod has gained electrons so it becomes negatively charged

  • These oppositely charged objects are also attracted to each other

• When an uncharged cloth is rubbed against an uncharged acetate plastic rod, however

  • Electrons are transferred away from the acetate rod to the cloth

    • The cloth has gained electrons so it becomes negatively charged

    • The rod has lost electrons so it becomes positively charged

Static charge transfer

• Sticking a balloon to the wall:

  • Rubbing a balloon on a woollen jumper transfers electrons onto the balloon

  • The balloon is now negatively charged whilst the jumper is left positively charged

  • The wall is still neutral, however, when the balloon is placed near the wall, the electrons in the wall are repelled by the balloon creating a net positively charged are that the balloon is attracted to

  • Since opposite charges attract, the balloon sticks to the wall

• Other examples of static electricity in everyday life are:

  • Dust and dirt attracted to TV screens and computer monitors

  • Dust build-up on the edges of a fan

  • Clothes clinging to each other after being in a tumble dryer, especially those made of synthetic fabrics

  • Hair sticking up after pulling a hat off

  • Combing dry hair with a plastic comb and the hair stays attracted to the comb

  • A child's hair sticking up after going down a plastic slide

  • Photocopiers use black powder to stick to white paper to create a copy of a document

  Examples of static electricity

• These experiences are most common in dry air conditions

• When it is much harder for the charges to dissipate so they build up instead, and make static electricity more noticeable

• Some of these can cause sparking

Sparking

• When electrostatic charge builds up it eventually needs to discharge, which it can do by sparking

• A static electric spark occurs when two oppositely charged objects have a large surplus of electrons

  • The surplus is so large that the charge 'jumps' across to a neutrally charged electrical conductor to discharge

  • Forming a small current called a spark

• After walking on a nylon carpet whilst wearing socks a charge is built up on your feet

  • If you then touch a metal door handle you will experience an electric shock

  • This is because of the spark passing from you to the door handle

An electric shock from a door handle

Lightning

• An extreme example of sparking is lightning

  • In a storm, clouds move over each other causing them to become charged when electrons are transferred between them

  • Since the ground is neutral, the negative charge jumps to meet the positive charges on the ground creating a big spark

  • This big spark is lightning