Topic 11 - Static Electricity

What happens when certain insulating material are rubbed against each other?

They become electrically charged(charged by friction)

One becomes positively charged whilst the other becomes negatively charged

How does charge by friction work?

When rubbing the 2 insulators, negatively charged electrons are charged from one material to the other

How can polythene rod be charged?

By rubbing it with a cloth, electrons are lost from the rod to the cloth

As such the rod becomes positively charged whilst the cloth becomes negatively charged

What happens between 2 oppositely charged objects

There is a force of attraction between them

What happens between 2 like charged objects

There is a force of repulsion between them

Examples of static electricity

shocks from everyday objects

lightning

a charged balloon sticking to a wall

a charged balloon picking up small pieces of paper

How are shocks caused from everyday objects

As 2 objects are charged by friction they become oppositely charged

a large surplus of electrons causes electrons to jump to a neutral object

Since current is the flow of electrons this causes a small current(a spark) to flow between the objects

How does lightning work?

In a storm clouds move over each other, which causes them to be charged when electrons are transferred between them

Since the ground is neutral the negative charges from the jump meet the positive charges on the ground(it has + and - charges) and a large spark is created aka lightning

How does a charged balloon stick to the wall?

By rubbing a balloon on a jumper it becomes negatively charged

The wall is neutral but when the balloon is placed near the wall the negative electrons are repelled by the negative balloon

This leaves a region of wall with a net positive charge allowing attraction to occur

How to induce a charge

By holding a negatively charged object near a neutral object, the electrons are repelled and it becomes positively charged

In other words, the neutral object reorientates its electrons to have an opposite charge due to repulsion

earthing

the process of removing excess charge from a body/object via the movement of electrons

How does earthing work?

It is done by connecting the charged object to the earth using a conductor such as a wire.

A conductor is used as charge can flow through it

If a positively charged object is connected then electrons will be attracted up the conductor to cancel the net positive charge as opposite charges attract

If a negatively charged object is connected then electrons will travel down the conductor away from the object to cancel the net negative charge as like charges repel

How is static electricity used in insecticide sprayers?

The insecticide is given an electrostatic charge and since the droplets of insecticide are of the same charge they repel each other which ensures that the spray remains fine and covers a large area

How can static electricity be used in photocopiers?

Photocopiers use static electricity to copy paper documents, most commonly in black and white

An image of the document is projected onto a positively charged copying plate

The plate loses its charge in the light areas and keeps the positive charge in the dark areas (i.e the text)

A negatively charged black toner powder is applied to the plate and sticks to the part where there is a positive charge

The toner is then transferred onto a new blank sheet of white paper

The paper is heated to make sure the powder sticks (hence why photocopied paper feels warm)

The photocopy of the document is now made

How can static electricity pose dangers in everyday life?

Risk of electrocution e.g. from lightning

Risk of fire or explosion due to a spark being too close to a flammable gas/liquid

How can fuelling aeroplanes be dangerous as a result of static electricity

A build-up of static charge is a potential danger when refuelling aeroplanes

Fuel runs through pipes at a fast rate

This fuel is very flammable

The friction between the fuel (a liquid insulator) and the pipe causes the fuel to gain charge

If this charge were to cause a spark, the fuel could ignite and cause an explosion

How can the danger of refuelling aeroplanes via static electricity be prevented?

Using a copper wire called the bonding line

The conductor earths the plane by carrying the charge through to the Earth which removes the risk of any sparks

What does a charged object create?

An electric field around itself

electric field

A region where an electric charge experiences a force

What happens when a charged object enters a positive/negative electric field?

Experiences a force of either attraction or repulsion depending on the charge of said object

What is the relationship between the strength of force of attraction/repulsion and distance?

If the 2 objects are closer together, then the force is stronger

What does an electric field pattern from oppositely charged spheres look like?

comes out of positive into negative

What does an electric field pattern from oppositely charged parallel plates look like?

straight lines coming out of the positive into the negative

How to represent the strength of an electric field?

The closer the field lines are together, the stronger they are

The further apart they are, the weaker they are

How do electric fields explain non contact forces?

Whilst the electric field cannot be seen the object in said field can move in it due to the electric force

What happens if an electric field becomes strong enough?

the charges are forced through insulators such as air creating a spark