static electricity

Question 1

What is a conductor? + examples

Answer 1

A material that allows the flow of electricity through it
Copper, steel, iron

Question 2

What is an insulator? + examples

Answer 2

A material that does not allow the flow of electricity through it
Nylon, perspex, air, plastic, wood, glass, rubber

Question 3

How are charges formed on objects?

Answer 3

By the movement (either loss or gain) of electrons.
Two insulating materials can be rubbed together to result in the two materials being charged

Question 4

What are the laws of attraction + repulsion?

Answer 4

Like charges repel
Opposite charges attract

Question 5

How is polythene charged?

Answer 5

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

Question 5

How is perpex charged?

Answer 5

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

Question 6

How does lightning strike?

Answer 6

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

Question 7

What is induced charge?

Answer 7

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

Question 8

Give an example of induced charge being used

Answer 8

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.

Question 9

How do lightning rods work?+ what are they

Answer 9

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.

Question 10

List uses of static electricity

Answer 10

Smoke precipitators
Inkjet printers
Photocopiers
Paint spraying

Question 11

List dangers of static electricity

Answer 11

Fueling at petrol stations
Fuel tanks fueling planes
Flammable substances storage

Question 12

How does the Van de Graaf generator work?

Answer 12

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

Question 13

How does the gold leaf electroscope work?

Answer 13

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

Question 14

What is a Coulomb meter?

Answer 14

A Coulomb meter shows the amount of charge on an object and whether it is positive or negative

Question 15

Why will a man walking on a non conducting surface become positively charged?

Answer 15

The electrons in the man will flow to the ground, therefore leaving him positively charged

Question 16

Why may people walking on nylon carpets in dry weather get a shock if they touch a radiator or metal door knob?

Answer 16

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

Question 17

What can prevent the buildup of electrostatic charges

Answer 17

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

Question 18

Why is the build up of electrostatic charge dangerous when filling up petrol?

Answer 18

The static electricity can cause sparks between the fuel pipe and the fuel causing the petrol to catch fire as it is highly flammable

Question 19

How do smoke precipitators work?

Answer 19

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

Question 20

Why should mobile phones not be used in petrol stations?

Answer 20

Mobile phones can get statically charged and can cause sparks that can set fire to the petrol

Question 21

What is electrostatic discharge?

Answer 21

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

Question 22

What happens when the gold leaf electroscope is touched?

Answer 22

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

Question 23

What happens when the charged polythene is taken away from the golf leaf electroscope?

Answer 23

The electroscope is now positively charged
The gold leaf stays as is

Question 24

Why is fueling planes a danger of static electricity?+ how can the danger be avoided?

Answer 24

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

Question 25

How do photocopiers work?

Answer 25

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.

Question 26

How does static electricity help with paint spraying?

Answer 26

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

Question 27

Why do metals prevent the build up of static electricity

Answer 27

The charges redistribute themselves in metals

Question 28

How do flammable substances need to be stored?

Answer 28

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

Question 29

Why do people who work on the components inside a computer wear earthed bracelets?

Answer 29

These bracelets stop the people from getting statically charged and getting electric shocked