Unit 4 Unit 4 Understanding Electricity

Topic 1 – Electric Charges

 Have you ever stuck a balloon to the wall after rubbing it on your head?  Have you ever got an electric shock off your door knob?  Have you ever seen lightening?

All these things happen because of Static Electricity

What is Static Electricity?  Static electricity occurs when there is a build up of electric charge on the surface of a material.  It is called static electricity because the charges don’t move.  The electricity we use everyday involves moving charges.

What is charge?  To understand charge we have to look at things on an extremely small scale.  We have to try and understand things that we can’t even see with the most powerful microscope. Atoms!

The atom  Everything we see around us everyday is made of atoms.  We can’t see individual atoms because they are so small.  In fact the diameter of an atom is about m

What is inside the atom?  The atom is made of 3 sorts of particles. The electron The proton The neutron  We can imagine each as a tiny little ball.

Inside an atom  The protons and neutrons sit together in a lump in the middle called the nucleus.  The electrons orbit around the nucleus, a bit like the planets orbiting the Sun.

Charge  The electron is negatively charged.  The proton is positively charged.  The neutron has no charge, it is neutral.

Charge neutral  Most things have the same number of electrons and protons in them. We say they are neutral don’t have  They don’t have any overall charge.

How do charges behave?  What do you know about magnets?  2 north poles will repel each other, but a north and a south put together will attract one another. opposites attract, likes repel.

How do charges behave?  Exactly the same thing happens with charges.  2 positive charges put together will repel each other.  Put a positive charge near a negative charge and they will attract each other.  A charged object may even attract a neutral one.  These are called the Laws of Charges

Static electricity  Static electricity is caused when certain materials are rubbed against each other.  Electrons can be rubbed off one material and on to another.  The material that has got extra electrons is now negatively charged  The material which has lost electrons is positively charged.

Static electricity  It is this imbalance of positive and negative charges that causes:  Balloons to stick to walls.  Your hair to stand on end when brush your hair on a dry day.  And the electric shock you sometimes get from the door handle.

Key Concept Review How does a proton differ from an electron? What does it mean to be “statically charged”? Explain how a Van de Graaff generator builds up static charge. A) What happens when like charges interact? B) What happens when unlike charges interact? Connect Your Understanding A neutral object contains no charge. Is this statement accurate? Explain Why is a neutral object attracted to a charged object? You bring a negatively charged rod close to some tiny pieces of plastic. Some of the pieces jump up the rod, but as soon as they make contact, they immediately fly away from the rod. Explain.