# 2.4.2 Static Electricity

### Static Electricity

• Static electricity is the stationary electric charge which is produced by friction which causes sparks, or the attraction of other small objects such as dust or hair
• This is caused by the imbalance between negative and positive charges in two objects
• This only works for insulators, since in conductors, the charge will move through them instead of remaining stationary
• Static electricity and sparking is produced by rubbing surfaces which causes insulators to become charged by friction
• This applies to solids, liquids and gases

• All objects are initially electrically neutral, meaning the negative (electrons) and positive charges are evenly distributed
• However, when the electrons are transferred, one object becomes negatively charged and the other positively charged
• This difference in charges leads to a force of attraction between itself and other objects which are also electrically neutral, by attracting the opposite charge to the surface of the objects they are attracted to

Electrons are rubbed onto the cloth leaving the cloth negatively charged and the rod positively charged

• One example is sticking a balloon to the wall:
• Rubbing a balloon on a woolen jumper transfers electrons onto the balloon by friction
• 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 positive charges in the wall are brought to the surface because they are attracted to the negative charge of the balloon
• Since opposite charges attract, the balloon sticks to the wall from only the electrostatic attraction
• 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

Common examples of static electricity

• These experiences are most common in dry air conditions
• This is because 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
• Feel free to try the following examples yourself after charging a balloon by rubbing it against a surface such as a cloth:
• Hover the balloon over small pieces of paper and they will jump up to it
• Place the balloon near a wall or curtain and it will stay there
• Place it over your (or your friends) hair and it will lift up some strands

#### Sparking

• The build-up of electrostatic charge can be quite dangerous and can cause sparking (also known as an electric shock)
• A static electric spark occurs when two objects which are charged by friction and become oppositely charged and have a surplus of electrons so large that the electrons ‘jump’ across to an object that is neutral
• Since a current is the flow of electrons, this causes a small current to flow between the objects, called a spark
• An example of sparking is the small electric shock felt from touching a door handle, or another person, after walking on a vinyl floor or nylon carpet with rubber shoes or whilst wearing socks

Examples of sparking from touching a door handle or another person

• 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 is what is known as lightning

Lightning is caused by the build up of charge in clouds

• Sparks can become quite dangerous and can cause a fire by igniting flammable gases and liquids, such as petrol

#### Exam Tip

Answers to exam questions in this topic are mainly looking for the words ‘friction‘ and the transfer of ‘electrons‘. Avoid saying the transfer of ‘charge’ since this is too vague and will not get you full marks

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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