Electrical Charges and Static Electricity

 
In this science article we learn how electromagnetic forces cause static electricity.

Before we consider what causes static electricity we look at some examples…

crowned crane meme with words, " I told you it was a bad idea to rub my hair with a balloon!"

 You hold a balloon, rub it on your hair and stick it to the wall.

balloon adheres itself to a wall

You walk across a carpet, take hold of a metal door handle and receive an electric shock.

receiving static electric shock from opening a door

 You remove your washing from a tumble dryer and your dry washing sticks together.

tumble dryer spinning with clothes inside

You turn off the TV and hear a ‘crackling’ sound.

flat screen tv

You whizz down a plastic slide and your hair sticks up on end!

 blond hair of girls stands on end after sliding down a green slide

After you have combed your hair you turn on the tap and a trickle of water bends to one side.

 a charged comb bends a flow of water

sciencenet.com.au

You comb your hair and your comb then pick up bits of paper.

pink comb picking up scraps of paper

sciencenet.com.au

Magnetism revisited

Do you remember how in Properties of Magnets we discussed how magnets have north and south poles? How opposite poles attract and same poles repel? How magnetism can be described as a ‘force from a distance’?

Magnets have electromagnetic forces that remain ‘constant’- that is the forces of magnetic attraction and repulsion do not change.

A north pole of a magnet will always attract another south pole. A south pole will always repel another south pole. A north pole will always repel another north pole.

Static electricity and magnetism

Static electricity behaves in exactly the same way as magnets do -‘opposites forces’ attract and ‘same forces’ repel. With static electricity we talk in terms of ‘electric charges’ attracting and ‘electric charges’ repelling.

Unlike magnets, the forces of static electricity do not remain ‘constant’ and are only temporary.

How do we make static electricity?

Look at this photo of the ‘girl with the blue balloon’.She is holding the balloon above her head.

girl with blue balloon no attraction

This is what the positive and negative ‘electrical charges’ on the surface of the balloon and in her hair look like.

balloon positive and negative charges before polarisation

The girl then does something which cause the hairs on her head to be attracted to the balloon.

  • What has she done?

hair on head of girl sticking to balloon

By rubbing the balloon on her head she has created ‘friction.’Friction produces heat and also gives extra energy to the electrical charges present both on the surface of her hair and on the surface of the balloon.

Friction is an incredibly powerful force. Try rubbing your hands together and feel what happens!

rubbing hands together causes friction

When you have too much energy, what do you do? Electrical charges are no different!

children running have plenty of energy

After the girl has rubbed her hair with the balloon the negative electrical charges from her hair jump onto the balloon.

With most of the negative electrical charges jumping onto the balloon this leaves the girl’s hair positively charged.

girl with blue balloon and positve and negative charges attract

So what is ‘static’ electricity?

‘Static’ means ‘being in one place’. So ‘static electricity’ means ‘electricity that stays in one place’. You notice that the electrical charges now ‘stay in one place’ (ie- they remain ‘static’)

 positve and negative charges attract

The electrical charges do not stay in one place for long…It is not natural for ‘materials’ to have more negative electrical charges than positive ones, or more positive electrical charges that negative ones. (called  a ‘polarisation’ of charges) All materials want to have the SAME number of positive and negative electrical charges.

This ‘polarisation’ of electrical charges is only temporary. (ie the state in which the balloon is negatively charged and the girl’s hair is positively charged does not last forever)

  • How do the charges become ‘equalized’ to a state in which both the balloon and the girl’s hair have equal numbers of positive and negative charges?

The answer is that ‘excess’ negative charges on the balloon will be lost to the atmosphere. ‘Negative’ charges from the atmosphere will also be attracted to the girl’s hair to equalize the positive charges in her hair. This will mean that both the girl’s hair and the balloon will go back to having the same number of positive and negative charges.

balloon positive and negative charges equalised

If the atmosphere is wet and there is a lot of moisture in the air the process of equalising the positive and negative charges can be very fast. If the atmosphere is very dry and there is little moisture in the air the process of equalisation can be very slow.

The girl could be left with sore arms if she continues to hold the balloon above her head at the same time as waiting for her hair to return to the top of her head!

Other ways in which electrical charges can be ‘equalized’

Sometimes there can be a sudden and violent discharge of negative electrical charges. When this happens sparks can fly!!! You can investigate the phenomenon of lightning strikes at Weatherwisekids.com

lightning strike which sets a tree alight! Amazing sight!

Science experiments -static electricity

  • Describe different sources of static electricity
  • Static electricity experiments for schools from the University of Virginia

Science Experiments-fun stuff

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