Static Electricity

The charge of a particle is either what?

• positive

• negative

• neutral (no charge)

What is the charge of electrons?

Protons?

Neutrons?

• negative

• positive

• neutral

This is why the number of electrons in a neutral atom is … to the number of protons

equal

What happens when two charged particles or objects are close together?

they also exert a force on each other

The force could either be what?

• attractive (the objects get closer together)

• repulsive (the objects move further apart)

Whether two objects attract or repel depends on what?

their charge

• if the charges are the opposite, they will attract

• if the charges are the same, they will repel

What type of force is attraction and repulsion between two charged objects an example of?

• non-contact force

• this is a force that acts on an object without being physically in contact with it

When certain insulating objects are rubbed against each other, they become what?

What is this called?

• electrically charged

• charging by friction

Where do the charges remain and what can they not do?

What happens to the objects?

• the charges remain on the insulators and cannot immediately flow away

• one gains a net positive charge and the other gains a net negative charge

What is an example of this?

an acetate plastic rod being charged by rubbing it with a cloth

• both the rod and cloth are insulating materials

Charging by friction occurs due to what?

due to the movement of electrons

What happens when an acetate rod is rubbed with a cloth?

negatively charged electrons are transferred from the rod to the cloth

• the cloth has gained electrons, so it becomes negatively charged

• the rod has lost electrons, so it becomes positively charged

What if a polythene rod is used?

• the electrons are transferred from the cloth to the rod

• the rod gains a negative charge

• the cloth gains a positive charge

At GCSE level, if you are asked to explain how charge is gained or lost, you must reference … If an object gains electrons, it gains negative charge and if it loses electrons it loses negative charge (and hence, gains positive charge)

electrons

Remember when charging by friction, it is only the … that can move, not any 'positive' charge, therefore if an insulator gains a negative charge, the other insulator must have gained a positive charge

electrons

What is electricity caused by?

the movement of charge in a circuit

What is static electricity caused by?

Where does this occur?

• a build up of stationary charge on a surface

• occurs on the surfaces of insulators

List 4 examples of static electricity

• the accumulation of dust particles on surfaces

• hair sticking up after combing it with a plastic comb or going down a plastic slide

• rubbing a balloon and sticking it to a wall

• sparking

All objects are initially electrically what?

What does this mean?

• neutral

• means the negative and positive charges are evenly distributed within the object

When charged objects are brought near to each other, what can be observed?

What if it’s two objects with different types of charge?

What about with the same charge?

• forces of attraction or repulsion can be observed

• force of attraction is observed

• force of repulsion is observed

explain what happens when sticking a balloon to the wall

• rubbing a balloon on a woolly jumper transfers electrons onto the balloon by friction

• the balloon becomes negatively charged, and the jumper becomes positively charged

• the wall is uncharged initially, but when the balloon is placed near the wall, the electrons on the balloon’s surface repel the electrons on the wall’s surface

• furthermore, the positive charges on the wall’s surface are attracted to the negatively charged balloon, which allows it to stick to the wall

What can the build-up of electrostatic charge lead to?

What is an example of this?

• sparking

• the small electric shock sometimes felt when a person touched a metal door handle

Sparking can occur when a … builds up on a person which is allowed to flow when they touch an earthed metallic object, such as a door handle

charge

A spark occurs between two objects when what?

• there is a large potential difference between the two objects

• which causes a current to flow between them

what is another example of sparking?

the small electric shock felt from touching another person after walking on a vinyl floor or nylon carpet with rubber shoes

Sparking can occur when a person with a large build up of … comes into contact with an uncharged person as there is a large potential difference between them

charge

What does sparking often occur between?

A charged insulator and an earthed conductor

What is an earthed conductor?

a wire, usually made from copper, that allows a current to flow to the Earth

what path will current always take?

the path of lower resistance

since copper has a lower resistance than, for example, a person, where will the current flow?

from the insulator to the earth through the copper wire rather than the person

What may happen when a potential difference between two objects becomes very large?

What can happen as a result of this?

Where can this be seen?

• the electric field may become strong enough to cause the breakdown of air

• as a result, an electrical discharge (large spark) can travel through the air to allow the current to flow

• in a Van de Graff generator or a lightning strike

What could the dangers of sparking be?

• electrocution e.g. by lightning

• ignition of a fire or explosion by a spark

What is lightning an extreme example of?

sparking

Describe lightning

• In a storm, ice crystals in clouds rub against each other causing a movement of electrons between them 

• The top of the cloud becomes positively charged, and the bottom becomes negatively charged

• The electrons on the ground are strongly repelled by the negative charge on the cloud, which causes it to become positively charged

• The potential difference between the cloud and the ground becomes increasingly large (~10⁶ V)

• Eventually, the cloud discharges a large spark as the negative charges jump to meet the positive charges on the ground

So essentially, what is lightning caused by?

the build-up of charge in clouds

What may sparking ignite when close to a flammable gas or liquid?

an explosion or fire

Explain how when refuelling aeroplanes, a build-up of static charge can pose significant danger

• As the fuel passes through a pipe, the friction between them causes static charge to build up

• If the potential difference becomes too large, it could cause a spark

• A spark could then ignite the fuel and cause an explosion

Explain how the risk of sparking can be reduced when refuelling a plane

• The risk can be reduced by connecting the fuel tank to the Earth with a wire called the bonding line

• The conductor earths the aeroplane by carrying excess charge through to the Earth and removes the risk of any sparks

When answering exam questions on static electricity, make sure to use keywords such as '…' and the transfer of '…'. Avoid saying the transfer of 'charge' since this is too vague and will not get you full marks unless you state it is the movement of  negative charge

• friction

• electrons

What does a charged object create?

And what is this similar to?

• an electric field around itself

• the way in which magnets create magnetic fields

What can the electric field be shown by?

electric field lines

Where do field lines always point?

away from positive charges and towards negative charges

What does the strength of an electric field depend on?

• the distance from the object created by the field:

• the field is strongest close to the charged object - this is shown by the field lines being closer together

• the field becomes weaker further away from the charged object - this is shown by the field lines becoming further apart

What will objects in an electric field experience?

an electrostatic force

since force is a vector, what does the direction of the force depend on?

whether the charges are the same or opposite

the force is either what?

attractive or repulsive

• If the charges are the same (negative and negative or positive and positive), this force will be repulsive and the second charged object will move away from the charge creating the field

• If the charges are the opposite (negative and positive), this force will be attractive and the second charged object will move toward the charge creating the field

what does the size of the force depend on?

what does this mean?

• the strength of the field at that point

• force becomes stronger as distance between two objects decreases and weaker as distance between two objects increases

The relationship between the strength of the force and the distance applies to both what?

the force of attraction and force of repulsion

two negative charges brought close together will have a … repulsive force than if they were far apart

stronger

What can an electric field be defined as?

A region in which a charged object will experience an electric force

Electric fields are represented by electric field lines that are always in what direction?

positive to negative

The electrical field lines for a charged, isolated sphere, such as a spherical conductor …

point away from the centre of a positive sphere

point towards the centre of a negative sphere

What is a uniform electric field such as that between two parallel plates?

straight lines from positive to negative

The electric field pattern between two oppositely charged spheres (or point charges) is slightly …

different

What does the electric field help to explain between charged objects since the electric field cannot be seen?

non-contact force, can be detected by another charged object that moves within that field due to the electric force

If an electric field becomes strong enough, the charges are forced through insulators such as air, creating a …

This is what happens for example, when a charged person touches a conductor

spark