© boardworks ltd 2005 1 of 44 physics static electricity

© Boardworks Ltd 20051 of 44

Physics

Static Electricity


Making static electricity

• Try out the following:

1. Cut up some small pieces of paper. Rub a biro in your school jumper and then hold the biro next to the pieces of paper – What happens?



• Try out the following:

2. Rub a biro in your school jumper and then hold the biro next to a gentle stream of water running from the tap – What happens?



Try out the following:

3. Blow up a balloon and rub it along your school jumper. Then hold the balloon next to your hair or the stream from the tap! What happens?


What is static electricity?

What do these things have in common?

Crackles when combing hair. Cling film sticking to your hands. Clothes clinging to each other

in a dryer. Getting a shock when rubbing

your feet on a carpet. Lightning.

They are all caused by static electricity.

Static electricity is due to electric charge that builds up on the surface of an object.


Where does static charge come from?

All materials are made of atoms,

The electrons have a negative charge.

The protons have a positive charge.

An atom has equal amounts of negative and positive charges which cancel each other out (- no overall charge)

electron (negative charge)

proton (positive charge)


Where does static charge come from?

When two materials are rubbed together electrons can be passed from one material to the other:

One material ends up with more electrons, so it now has an overall negative charge.

One material ends up with less electrons, so it now has an overall positive charge.


Charging a polythene rod


If an insulator made of polythene is rubbed with a cloth, electrons move from the cloth to the insulator.

The cloth becomes positively charged.

The insulator becomes negatively charged.

What charge does the cloth now have?

What charge does the polythene insulator now have?

Charging polythene


Charging an acetate rod


If an insulator made of acetate is rubbed with a cloth, electrons move from the insulator to the cloth.

Charging acetate

The cloth becomes negatively charged.

The insulator becomes positively charged.

What charge does the cloth now have?

What charge does the polythene insulator now have?


Investigating how charged objects react to each other


How do pairs of charges behave?


Pairs of charges – attract or repel?


Insulators

An object which holds onto a charge is called an electrical insulator – examples are plastic and wood.


Conductors

Electrical conductors allow electrical charge to pass through them.

•Examples: Metals, Ionic substances


Does water hold onto an electrical charge?

• Water is a (poor) conductor of electricity– it allows some electrical charge to pass through it.


Earthing

If a charged object is connected to the earth by a conductor then the electrical charge will flow into the earth.


Earthing

We say that the earth is a source and sink for electrons.


Examples of earthing

• lightening strike…


Why do you only get a shock off a trolley in dry weather?

© boardworks ltd 2005 1 of 44 physics static electricity

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