Static Electricity

Build-up of static is caused by friction

• When certain insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other
• This will leave the materials electrically charged, with a positive static charge on one and an equal negative static charge on the other
• Which way the electrons are transferred depends on the two materials involved
• The classic examples are polythene and acetate rods being rubbed with a cloth duster

\

Only electrons move- never positive charges

But +ve and -ve electrostatic charges are only ever produced by the movement of electrons. The positive charges definitely do not move.

A positive static charge is always caused by electrons moving away elsewhere. The material that loses the electrons loses some negative charge, and is left with an equal positive charge.

\
Too much static causes sparks

• As electric charge builds on an object, the potential difference between the object and the earth increases
• If the potential difference gets large enough, electrons can jump across the gap between the charged object and the earth-this is the spark
• They can also jump to any earthed conductor that is nearby-which is why you can get static shocks getting out of a car. A charge builds up on the car’s metal frame, and when you touch the car, the charge travels through you to earth
• This usually happens when the gap is fairly small

\

Like charges repel, opposite charges attract

• When two electrically charged objects are brought close together they exert a force on one another
• Two things with opposite electric charges are attracted to each other, while two things with the same electric charge will repel each other
• These forces get weaker the further apart the two things are
• These forces will cause the objects to move if they are able to do so. This is known as electrostatic attraction/repulsion and is a non-contact force
• One way to see this force is to suspend a rod with a known charge from a piece of string. Placing an object with the same charge nearby will repel with rod-the rod will move away from the object. An oppositely charged object will cause the rod to move towards the object

\