Electric Charge & Static Electricity

How do Charges Interact? Atoms contain charged particles called electrons and protons. The charge on a proton is positive (+) The charge on an electron is negative (-) Like charges repel each other Opposite charges attract each other

Vocabulary Electricity: The interaction between electric charges. Electric force: The energy between charged objects.

Vocabulary Electric Field: An area around a charged object where the object’s electric force is exerted on other charged objects. Electric fields get weaker the farther away they are from the charge.

How Does Charge Build Up? Most objects have no overall charge An atom (as you learned last year!!) usually has an equal number of protons and electrons – this makes the atom uncharged, or neutral. An uncharged object can become charged by gaining or losing electrons (the protons don’t move).

Vocabulary Static Electricity: The build up of charges on an object. Charges build up, but do not flow continuously (otherwise we would ALWAYS be getting shocked by things!)

Charging Objects Conservation of Charge: Charges are neither created nor destroyed If one object loses electrons, another MUST pick them up!

There are 4 methods by which charges can redistribute themselves to build up static electricity: 1.Friction 2.Conduction 3.Induction 4.Polarization

Friction The transfer of electrons from one uncharged object to another by rubbing the objects together.

Conduction The transfer of electrons from one object to another by direct contact. Sound familiar?!

Conduction Electrons move from negative > positive The ball is + and gains – from the girl touching it She starts out neutral, but loses e - This leaves her hair positively charged and the strands repel each other!

Induction & Polarization Electrons can react to the charged field of an object without touching the object itself. In some materials, like metals, electrons can easily leave their atoms. (Induction)

Induction When a metal object is close to a negatively charged object, electrons are repelled by the field and move away from it. The close end of the metal object become positively charged. The far end of the object becomes negatively charged. The opposite happens if the original object is positively charged.

Induction

Polarization In other materials (not metals), electrons move only within their own atoms. The electrons react to electric fields, resulting in individual atoms having charged ends that are attracted to charged objects.

Vocabulary Static discharge: The loss of static electricity as electric charges transfer from one object to another. Often produces a spark This is the electrons moving around and heating the air