Static electricity

Electrostatic charge can be useful, but can also be dangerous.

Objects such as car panels and bike frames are often painted with an electrostatic paint sprayer. The spray nozzle is connected to a positive terminal. As the paint droplets pass through it, they pick up a positive charge. The paint drops repel each other so they spread out to form a fine cloud. The item being painted is connected to a negative terminal so the positively charged droplets are attracted to it.

In a photocopier, a copying plate is given a charge. An image of the page to be copied is projected onto the charged plate. Where light hits the plate the charge leaks away, leaving a pattern of the page. Black ink powder is attracted to the charged parts of the plate. This powder is transferred onto a piece of paper. The paper is heated so the powder melts and sticks to it, producing a copy of the original page.

When charge flows through a conductor there is a current in it. Electric current is the rate of flow of charge.

In a solid conductor the charge carriers are electrons.

Metals are good conductors of electricity because they contain free, conduction electrons that are not confined to a single atom.

Insulators cannot conduct because all the electrons are held in atoms.

A conductor can only hold charge if it is isolated from the ground. Otherwise electrons will flow to or from the earth and discharge it.

Electric current is the rate of charge.

When two electrically insulating materials are rubbed together electrons are rubbed off one material and deposited on the other. It depends on the material that is used on which which way the electrons are transferred.

Electrons have a negative charge so the material that has gained electrons becomes negatively charged. The one that has lost electrons is left with a positive charge.

Two objects that have opposite electric charges are attracted to each other. Two objects that have the same electric charges repel each other. The bigger the distance between the objects, the weaker the force.

Like charges repel; unlike charges attract

Insulating materials that LOSE electrons when rubbed become positively charged

Insulating materials that GAIN electrons when rubbed become negatively charged