static electricity Flashcards
What is a conductor? + examples
A material that allows the flow of electricity through it
Copper, steel, iron
What is an insulator? + examples
A material that does not allow the flow of electricity through it
Nylon, perspex, air, plastic, wood, glass, rubber
How are charges formed on objects?
By the movement (either loss or gain) of electrons.
Two insulating materials can be rubbed together to result in the two materials being charged
What are the laws of attraction + repulsion?
Like charges repel
Opposite charges attract
How is polythene charged?
When polythene is rubbed, the electrons rub off the cloth and onto the polythene.
This leaves the polythene negatively charged (it has gained electrons), and the cloth positively charged (it has gained electrons
The magnitude of both charges is the same as they have both lost or gained the same number of electrons
How is perpex charged?
When perspex is rubbed, the electrons rub off the perspex and onto the cloth.
This leaves the perspex positively charged (it has lost electrons), and the cloth negatively charged (it has gained electrons)
The magnitude of both charges is the same as they have both lost or gained the same number of electrons
How does lightning strike?
Electric charge builds up in clouds due to the rubbing of ice particles against each other
The top of the cloud becomes positively charged and the bottom becomes negatively charged
This leads to the difference in charge between the earth and the cloud to become large
The charge on the bottom of the cloud discharges as a bolt of lightning strikes a positive area on the ground
What is induced charge?
A temporary charge that occurs when a charged object is brought near an uncharged object.
The charge is removed when the objects are moved away from each other
Give an example of induced charge being used
Induced charge is how balloons stick to walls
When a negatively charged balloon is brought near a wall, it creates an induced charge in the wall.
The electrons in the balloon repel the electrons in the wall away from them
The protons in the wall are attracted to the electrons in the balloon
Bringing the unlike charges together and so allowing the balloon and wall to be attracted to each other.
How do lightning rods work?+ what are they
A lightning rod is a strip of copper that runs down the side of a building to the ground
The negative charges in the cloud repel the negative charges in the lightning conductor away, causing the lightning conductor to become positively charged (extra concentration of positive charges on the buildings and lightning conductor)
The lightning conductor attracts negative charges in the air, leaving behind positive charges that neutralise the cloud
This means the cloud does not have any static electricity that can be discharged, and so lightning does not strike.
List uses of static electricity
Smoke precipitators
Inkjet printers
Photocopiers
Paint spraying
List dangers of static electricity
Fueling at petrol stations
Fuel tanks fueling planes
Flammable substances storage
How does the Van de Graaf generator work?
The belt inside the generator rubs electrons off onto the dome, leading to the dome becoming negatively charged
In the other dome (the earthed dome), the overall charge is positive or neutral
When the difference in charge between the two domes is big enough, a spark can be seen between them when they are close enough
How does the gold leaf electroscope work?
When a charged polythene rod is held near the disc on top of the gold leaf electroscope,
The negative charges are repelled to the bottom of the electroscope
Therefore the leaf is repelled away from it
What is a Coulomb meter?
A Coulomb meter shows the amount of charge on an object and whether it is positive or negative
Why will a man walking on a non conducting surface become positively charged?
The electrons in the man will flow to the ground, therefore leaving him positively charged
Why may people walking on nylon carpets in dry weather get a shock if they touch a radiator or metal door knob?
When people walk on nylon carpets, the electrons from the carpet will rub off onto them
This gives them a negative charge and when they touch metals the charge flows to the earth (is earthed), giving them an electric shock
What can prevent the buildup of electrostatic charges
The electrostatic charges can be conducted via conducting materials e.g. metals as they don’t charge by static electricity
Earthing wires can also prevent the buildup of static electricity as they ensure that the charge flows to the earth instead of the charge building up
Why is the build up of electrostatic charge dangerous when filling up petrol?
The static electricity can cause sparks between the fuel pipe and the fuel causing the petrol to catch fire as it is highly flammable
How do smoke precipitators work?
Smoke particles pass through a negatively charged grid, causing them to be negatively charged
Therefore they are attracted to the positively charged or neutral collection plates, allowing the other waste gases that don’t contain smoke particles to leave the chimney
The collection plates are knocked to remove the smoke particles
Why should mobile phones not be used in petrol stations?
Mobile phones can get statically charged and can cause sparks that can set fire to the petrol
What is electrostatic discharge?
Discharge occurs when an object becomes uncharged
The electrical charge gathered on an object will leak away as the charges are transferred through the air
Objects can discharge at different speeds depending on the humidity air pressure and temperature
What happens when the gold leaf electroscope is touched?
If the disc is touched (even when there is a charged polythene rod near), the electrons flow to the ground (this is the disc being earthed)
The overall charge of the electroscope is now positive
The gold leaf stays as it is
What happens when the charged polythene is taken away from the golf leaf electroscope?
The electroscope is now positively charged
The gold leaf stays as is
Why is fueling planes a danger of static electricity?+ how can the danger be avoided?
An aircraft may become charges when it flies through the air due to friction between the air and the plane
Sparks can occur between the fuel nozzle and the plane causing the fuel to catch fire
At fueling stations, a copper cable is attached from the plane to the ground, neutralising the plane (by earthing it)
Refueling hoses can also be made out of metal to stop the build up of electrical charge
How do photocopiers work?
The original image is projected onto a positively charged copying plate
The parts of the drum which are lit by the projected image lose their electrostatic charge when they start to conduct.
A black powder (called toner) is negatively charged.
The toner is attracted to the positively charged parts of the drum.
The drum rotates and rolls against a piece of copier paper.
The toner is transferred from the drum to
the paper making a black and white image of the original.
Finally, the paper is heated which makes the toner stick to it.
How does static electricity help with paint spraying?
An object is negatively charged or neutral
This can be done by connecting the object to the negative side of a battery
When the paint is sprayed, positively charged droplets repel each other and form a fine spray
The paint droplets are charged as the metal spray nozzle is positively charged
Why do metals prevent the build up of static electricity
The charges redistribute themselves in metals
How do flammable substances need to be stored?
In containers made out of conducting materials, or they need to be handled on surfaces that are made of conducting materials
This prevents sparks being created due to the build up of charge, and therefore prevents the substances catching fire due to these sparks
Why do people who work on the components inside a computer wear earthed bracelets?
These bracelets stop the people from getting statically charged and getting electric shocked
