Static electricity

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Notas de aula

Electric Charge and Particles

The charge of a particle can be positive, negative, or neutral (no charge).
Electrons are negatively charged, protons are positive, and neutrons are neutral.
In a neutral atom, the number of electrons equals the number of protons, so the overall charge is zero.
An object becomes negatively charged when it gains electrons and positively charged when it loses electrons.
When two charged objects are close, they exert a force on each other: attractive if opposite charges, repulsive if like charges.
Attraction and repulsion between charged objects are examples of non-contact forces.

Charging by Friction

When certain insulating materials are rubbed together, they become electrically charged – this is charging by friction.
The charges remain on the insulators and cannot easily flow away.
Charging by friction happens because negatively charged electrons are transferred from one material to the other.
The material that gains electrons becomes negatively charged; the material that loses electrons becomes positively charged.
For example, rubbing an acetate rod with a cloth transfers electrons from the rod to the cloth: the rod becomes positive, the cloth negative.
If a polythene rod is rubbed with a cloth, electrons transfer from the cloth to the rod: the rod becomes negative, the cloth positive.
Only electrons move – positive charge is not transferred.

Apparatus for demonstrating charging by friction using a polythene rod and another insulating material.

Static Electricity and Sparking

Static electricity is caused by a build-up of stationary charge on the surface of insulators.
A spark occurs when there is a large potential difference between two objects, causing a current to flow between them.
Sparking can happen when a charged person touches an earthed metal object, like a door handle.
An earthed conductor is a wire (often copper) that allows current to flow to the Earth; current takes the path of lower resistance.
If the electric field becomes strong enough, it can force charges through insulators like air, causing an electrical discharge (spark).
Examples include the small shock from a car door and lightning.

Examples of Static Electricity

Rubbing a balloon on a woolly jumper transfers electrons to the balloon, making it negatively charged and the jumper positively charged.
The balloon sticks to a neutral wall because the negative balloon repels electrons in the wall, leaving a positive region that attracts the balloon.
A charged comb can pick up small pieces of paper: the comb repels negative charges in the paper, leaving a positive surface that is attracted to the comb.
Hair sticks up after combing with a plastic comb because strands gain the same charge and repel each other.
Dust accumulation on surfaces is another example of static electricity.

Dangers of Static Electricity

A spark near flammable gases or liquids can cause a fire or explosion.
When refuelling aeroplanes, friction between fuel and pipes can build up static charge; a spark could ignite the fuel.
The risk is reduced by connecting the fuel tank to the Earth with a bonding line – a copper wire that carries excess charge to the ground.
Lightning is an extreme example of sparking: charge builds up in clouds and discharges to the ground.
Electrocution is another danger of static electricity.

Uses of Static Electricity

Photocopiers use static electricity: an image is projected onto a positively charged plate, which loses charge in light areas.
Negatively charged toner powder sticks to the remaining positive areas and is then transferred to paper and heated to fix it.
Inkjet printers work similarly, using negatively charged ink droplets attracted to the correct place on the page.
Insecticide sprayers give droplets an electrostatic charge so they repel each other, forming a fine mist that covers a large area.
The charged droplets are also attracted to the Earth, reducing drift.
Spray painting of cars uses the same principle.

Electric Fields

A charged object creates an electric field around itself – a region where a charged object experiences a force.
Electric field lines point away from positive charges and towards negative charges.
The field is strongest close to the charged object (field lines closer together) and weaker further away (field lines further apart).
Around an isolated charged sphere, field lines are radial: away from a positive sphere, towards a negative sphere.
Between two parallel plates, the field is uniform: straight, parallel lines from positive to negative.
The force on a charged object in a field is stronger when the distance between the objects is smaller.

Fields and Static Phenomena

The electric field explains the non-contact force between charged objects: a second charged object in the field experiences a force.
If the charges are the same, the force is repulsive; if opposite, the force is attractive.
The force becomes stronger as the distance between the charged objects decreases.
If an electric field becomes strong enough, charges are forced through insulators like air, creating a spark.
This explains sparking when a charged person touches a conductor.
Earthing removes excess charge: a positively charged object attracts electrons from Earth, while a negatively charged object sends electrons to Earth.

Slides

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Questões de prática

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1.Which particle is transferred when an insulating material becomes charged by friction?
Easy
- AElectron
- BProton
- CNeutron
- DAtom
2.An object becomes negatively charged when it:
Easy
- Agains electrons
- Bloses electrons
- Cgains protons
- Dloses protons
3.Two charged objects are brought close together and attract each other. Which statement about their charges is correct?
Easy
- AThey carry opposite charges
- BThey carry the same charge
- CBoth must be neutral
- DBoth must be positive
4.Which of the following statements about electric field lines is correct?
Easy
- AThey point away from positive charges and towards negative charges
- BThey point away from negative charges and towards positive charges
- CThey point from negative to positive charges
- DThey have no direction
5.A positively charged object is connected to earth by a wire. What happens to the charge on the object?
Medium
- AElectrons flow from earth to the object and neutralise it
- BElectrons flow from the object to earth
- CProtons flow from earth to the object
- DNothing happens because the object is an insulator
6.A negatively charged rod is held near a small piece of paper. The paper is attracted to the rod. Why?
Medium
- AThe rod repels electrons in the paper, leaving a positive region that is attracted
- BThe paper has a positive charge
- CThe rod transfers electrons to the paper
- DThe paper is an insulator so it cannot be attracted
7.A student rubs a polythene rod with a cloth. The rod becomes negatively charged. Which row correctly describes the charge on the cloth?
Medium
- APositive, equal in size
- BPositive, larger
- CNegative, equal in size
- DNegative, smaller
8.Which of these is a correct definition of an electric field?
Medium
- AA region where a charged object experiences a force
- BA region where a magnetic material experiences a force
- CA region where only positive charges can exist
- DA region where electrons are always stationary

Mais perguntas

9.Which of the following statements about static electricity are correct? (select all that apply)
Medium
- AStatic charge builds up on insulators
- BElectrons are transferred when insulators are rubbed together
- CLike charges attract each other
- DThe force between two charged objects is a non-contact force
- EProtons are transferred from one insulator to another
10.Which of the following are true about the electric field around a charged object? (select all that apply)
Hard
- AThe field is strongest close to the charged object
- BThe field lines point towards a negative charge
- CThe field becomes stronger as you move further away
- DThe field lines are closer together where the field is stronger
- EThe field lines point away from a negative charge
11.Two objects with the same type of charge repel each other.
Easy
True or false?
12.An object becomes positively charged by gaining protons.
Easy
True or false?
13.Electric field lines are drawn with arrows pointing away from positive charges and towards negative charges.
Easy
True or false?
14.A spark occurs when there is a large potential difference between two objects.
Medium
True or false?
15.Match each term with its correct description.
Medium
- Attraction
- Repulsion
- Earthing
- Sparking
- Force between opposite charges
- Force between like charges
- Removing excess charge by connecting to the Earth
- A flow of charge through air due to a large potential difference
16.Put the steps in the correct order to describe how a balloon becomes charged and sticks to a wall.
Medium
- The balloon is rubbed on a woolly jumper
- Electrons are transferred from the jumper to the balloon
- The balloon becomes negatively charged
- The balloon is brought near the wall and induces a positive charge on the wall's surface
- The balloon sticks to the wall due to electrostatic attraction
17.Match each term about static electricity with its correct description.
Medium
- Charging by friction
- Earthing
- Electric field
- Sparking
- The process of removing excess charge from an object by connecting it to the Earth
- A region where a charged object experiences a force
- A sudden flow of charge between two objects with a large potential difference
- The transfer of electrons between two insulating materials that are rubbed together
18.Put the steps in the correct order to explain why a balloon sticks to a wall after being rubbed on a woolly jumper.
Medium
- The balloon is rubbed on the jumper, transferring electrons to the balloon.
- The balloon becomes negatively charged and the jumper becomes positively charged.
- The wall is initially neutral, but the negative balloon repels electrons on the wall's surface.
- The wall's surface becomes positively charged and attracts the negative balloon.
- The balloon sticks to the wall due to electrostatic attraction.
19.Which of the following statements about sparking are correct? (select all that apply)
Medium
- AA spark occurs when there is a large potential difference between two objects.
- BSparking can be reduced by earthing the charged object.
- CA spark is a flow of protons between two objects.
- DSparking can ignite flammable gases or liquids.
- EEarthing increases the build-up of static charge.
20.Which of the following statements about electric fields are correct? (select all that apply)
Hard
- AThe electric field is strongest close to a charged object.
- BElectric field lines point from negative to positive charges.
- CThe force on a charged object becomes stronger as the distance between objects decreases.
- DElectric field lines are closer together where the field is weaker.
- EAn electric field can exert a force on a charged object without contact.
21.Which of the following are examples of static electricity? (select all that apply)
Medium
- AA charged comb picking up small pieces of paper.
- BLightning during a storm.
- CA current flowing through a wire in a circuit.
- DA balloon sticking to a wall after being rubbed.
- EHair standing up after combing with a plastic comb.
22.Which of the following statements about charging by friction are correct? (select all that apply)
Medium
- AOnly electrons are transferred between the materials.
- BThe material that gains electrons becomes negatively charged.
- CThe material that loses electrons becomes negatively charged.
- DThe two materials end up with equal but opposite charges.
- EProtons are transferred from one material to the other.
23.Which of the following statements about earthing are correct? (select all that apply)
Hard
- AEarthing provides a path for charge to flow to or from the Earth.
- BEarthing a negatively charged object allows electrons to flow away from the object.
- CEarthing a positively charged object attracts electrons from the Earth.
- DEarthing increases the net charge on an object.
- EEarthing is used to prevent dangerous sparks.
24.A student rubs a polythene rod with a cloth. The rod becomes negatively charged. Which statements are correct? (select all that apply)
Hard
- AElectrons are transferred from the cloth to the rod.
- BThe cloth becomes positively charged.
- CThe rod gains protons from the cloth.
- DThe cloth and rod have charges of equal magnitude.
- EThe rod loses electrons to the cloth.
25.Which of the following are uses of static electricity? (select all that apply)
Medium
- APhotocopiers
- BInkjet printers
- CInsecticide sprayers
- DElectric heaters
- ECar spray painting
26.Which of the following statements about lightning are correct? (select all that apply)
Hard
- ALightning is caused by a build-up of charge in clouds.
- BThe bottom of a storm cloud becomes negatively charged.
- CThe ground becomes negatively charged due to repulsion.
- DA large potential difference causes a spark to jump between cloud and ground.
- ELightning involves a transfer of protons.
27.Which of the following statements about electric field lines around a positive point charge are correct? (select all that apply)
Medium
- AThey point radially outwards from the charge.
- BThey are closer together near the charge.
- CThey point radially inwards towards the charge.
- DThey are parallel straight lines.
- EThey indicate the direction of the force on a positive test charge.
28.A metal disc is held by an insulating handle above a negatively charged plastic block. The disc is momentarily earthed. Which statements are correct? (select all that apply)
Hard
- AElectrons in the disc are repelled to the Earth.
- BThe disc becomes positively charged.
- CThe disc becomes negatively charged.
- DEarthing allows charge to flow between the disc and Earth.
- EThe plastic block loses its charge.
29.In a neutral atom, the number of electrons is equal to the number of protons.
Easy
True or false?
30.A positively charged object has gained protons.
Easy
True or false?
31.Electric field lines are drawn pointing away from positive charges and towards negative charges.
Easy
True or false?
32.The electric field is strongest at the point furthest from a charged object.
Medium
True or false?
33.Earthing a charged object provides a path for electrons to flow to or from the Earth, reducing the net charge.
Medium
True or false?
34.A spark occurs when there is a small potential difference between two objects.
Medium
True or false?
35.Match each situation with the correct outcome.
Medium
- Two positive charges brought close together
- A positive and a negative charge brought close together
- A charged object connected to Earth by a wire
- A large potential difference between two objects
- They repel each other
- They attract each other
- Excess charge flows to or from the Earth
- A spark may jump between them
36.Match each term with its correct definition.
Medium
- Static electricity
- Electric field
- Earthing
- Spark
- A build-up of stationary charge on an insulator
- A region where a charged object experiences a force
- Connecting an object to the Earth to remove excess charge
- A sudden flow of charge through an insulator such as air
37.Put the steps in the correct order to describe how a lightning rod protects a building.
Medium
- A thundercloud becomes charged, creating a large potential difference with the ground.
- The electric field near the pointed rod becomes very strong.
- The rod allows charge to flow to or from the Earth, reducing the potential difference.
- The risk of a dangerous spark striking the building is reduced.
38.Put the steps in the correct order to describe how a photocopier uses static electricity.
Medium
- An image of the document is projected onto a positively charged plate.
- The plate loses charge in the light areas and keeps positive charge in the dark areas.
- Negatively charged toner powder is applied and sticks to the positively charged areas.
- The toner is transferred onto a blank sheet of paper.
- The paper is heated so the toner sticks, producing the copy.
39.A metal sphere is charged negatively and placed on an insulating stand. A second identical metal sphere, initially uncharged, is brought close to it without touching. Which statement describes the force between the spheres?
Medium
- AThere is a force of attraction because opposite charges are induced on the second sphere
- BThere is a force of repulsion because both spheres have the same charge
- CThere is no force because the second sphere is uncharged
- DThere is a force of attraction because the second sphere gains protons
40.A student wants to show that a plastic rod has gained an electric charge after being rubbed with a cloth. Which of the following is the most suitable method?
Medium
- AHold the rod near small pieces of paper and observe whether they are attracted to it
- BWeigh the rod on a balance to see if its mass has changed
- CPlace the rod in a beaker of water and observe whether it dissolves
- DMeasure the length of the rod with a ruler
41.Name the charged particle that is transferred when two insulators are rubbed together.
Easy
42.What is the name of the process of removing excess charge from an object by connecting it to the Earth?
Medium
43.A charged object has a potential difference of 1.5 × 10⁴ V relative to the ground. If the charge on the object is 2.0 × 10^-6 C, calculate the energy transferred when it is earthed. Use the equation: energy = charge × potential difference. Give your answer in joules.
Medium
44.Complete the sentence about charging by friction.
Easy
When a polythene rod is rubbed with a cloth, electrons are transferred from the cloth to the rod, so the rod becomes ____ charged and the cloth becomes ____ charged.
45.Complete the sentences about electric fields.
Medium
Electric field lines always point away from ____ charges and towards ____ charges. The field is strongest where the field lines are ____ together.
46.Which particle is transferred when two insulating materials are rubbed together to charge them by friction?
Easy
47.A charged object has a charge of 3.0 × 10^-6 C and a potential difference of 2.0 × 10⁴ V relative to the ground. Calculate the energy transferred when it discharges. Give your answer in joules.
Medium
48.During a lightning strike, a charge of 25 C is transferred between a cloud and the ground. The potential difference is 1.0 × 10⁸ V. Calculate the energy transferred. Give your answer in joules.
Hard
49.Complete the sentences about charging by friction using the words from the box: electrons, protons, positive, negative, neutral.
Medium
When a plastic rod is rubbed with a cloth, ____ are transferred from the cloth to the rod. The rod becomes ____ charged.
50.Complete the sentences about electric fields using the words from the box: positive, negative, stronger, weaker, closer, further.
Medium
Electric field lines point away from ____ charges and towards ____ charges. The field is ____ where the field lines are closer together.
51.During a lightning strike, a charge of 25 C is transferred between a cloud and the ground. The potential difference is 1.0 × 10⁸ V. Calculate the energy transferred, using the equation E = Q × V. Give your answer in joules.
Hard
52.Complete the sentences about charging by friction. Use each word once.
Easy
When an acetate rod is rubbed with a cloth, negatively charged ____ are transferred from the rod to the cloth. The rod therefore becomes ____ charged, and the cloth becomes ____ charged.
53.Explain how a plastic rod becomes positively charged when it is rubbed with a cloth.
Medium
54.Explain how the electric field concept helps to explain the non-contact force between two charged objects.
Hard
55.Explain how earthing prevents a dangerous spark when refuelling an aeroplane.
Hard
56.Explain how the concept of an electric field helps to explain the non-contact force between two charged objects.
Hard
57.A student rubs a polythene rod with a cloth. The rod becomes negatively charged. Explain how the rod becomes charged.
Hard
58.A charged object has a potential difference of 1.5 × 10⁴ V relative to the ground. If the charge on the object is 2.0 × 10^-6 C, calculate the energy transferred when it is earthed. Use the equation: energy = charge × potential difference. Give your answer in joules.
Medium
- A2.03 J
- B-0.97 J
- C0.03 J
- D1.03 J
59.A charged object has a charge of 3.0 × 10^-6 C and a potential difference of 2.0 × 10⁴ V relative to the ground. Calculate the energy transferred when it discharges. Give your answer in joules.
Medium
- A2.06 J
- B0.06 J
- C1.06 J
- D-0.94 J
60.During a lightning strike, a charge of 25 C is transferred between a cloud and the ground. The potential difference is 1.0 × 10⁸ V. Calculate the energy transferred. Give your answer in joules.
Hard
- A2750000000 J
- B3000000000 J
- C2250000000 J
- D2500000000 J
61.During a lightning strike, a charge of 25 C is transferred between a cloud and the ground. The potential difference is 1.0 × 10⁸ V. Calculate the energy transferred, using the equation E = Q × V. Give your answer in joules.
Hard
- A2500000000 J
- B3000000000 J
- C2250000000 J
- D2750000000 J

Flashcards

What are the three possible charge states of a particle?

Positive, negative, or neutral (no charge).

Which subatomic particles are negatively charged, which are positive, and which are neutral?

Electrons are negatively charged, protons are positive, and neutrons are neutral.

Why is a neutral atom neutral overall?

It has equal numbers of negative electrons and positive protons, so the opposite charges cancel out and the overall charge is zero.

How does an object become negatively charged?

It gains electrons.

How does an object become positively charged?

It loses electrons.

What happens when two objects with opposite charges are brought close together?

They attract each other.

What happens when two objects with the same type of charge are brought close together?

They repel each other.

Is the force between two charged objects a contact or non-contact force?

It is a non-contact force, because the objects exert a force on each other without touching.

What is charging by friction?

When certain insulating materials are rubbed against each other, electrons are transferred from one material to the other, leaving one positively charged and the other negatively charged.

When an acetate rod is rubbed with a cloth, electrons move from the rod to the cloth. What charge does each material end up with?

The cloth gains electrons and becomes negatively charged; the rod loses electrons and becomes positively charged.

When a polythene rod is rubbed with a cloth, electrons move from the cloth to the rod. What charge does each material end up with?

The rod gains electrons and becomes negatively charged; the cloth loses electrons and becomes positively charged.

Why can static charge build up on insulators but not easily on conductors?

Static electricity is a build-up of stationary charge on a surface. On insulators the charge cannot flow away, whereas conductors allow charge to move.

What is earthing?

Earthing (or grounding) is removing excess charge from an object by connecting it to the Earth with a conductor, allowing electrons to flow to or from the Earth.

When a positively charged object is earthed, which way do electrons move?

Electrons are attracted up through the conductor towards the positive object, cancelling out its net positive charge.

When a negatively charged object is earthed, which way do electrons move?

Electrons travel down the conductor away from the object and into the Earth, because like charges repel.

What is an electric field?

A region in which a charged object experiences an electric force.

Which direction do electric field lines point?

They always point away from positive charges and towards negative charges.

How is the strength of an electric field shown by field lines?

The field is strongest where the field lines are closest together, and weaker where they are further apart.

What does the electric field pattern look like around an isolated charged sphere?

The field lines are spherical: they point away from the centre of a positive sphere and towards the centre of a negative sphere.

What does the electric field between two parallel plates look like?

It is a uniform field: straight, parallel lines directed from the positive plate to the negative plate.

How does the force between two charged objects change as the distance between them decreases?

The force gets stronger as the distance decreases, and weaker as the distance increases. This applies to both attraction and repulsion.

What causes a spark between two charged objects?

A large potential difference between them causes a current to flow. If the electric field becomes strong enough, charges are forced through the air, creating a spark.

How does a lightning rod protect a building?

It is a pointed metal spike connected to the ground by a metal wire, so it provides a low-resistance path for charge to flow to the Earth, preventing a dangerous build-up of charge.

Why is a bonding line used when refuelling an aeroplane?

The bonding line is a copper wire connecting the fuel tank to the Earth. It carries excess charge to the ground, preventing a spark that could ignite the fuel.

How does a photocopier use static electricity?

A positively charged plate loses its charge in light areas and keeps it in dark areas. Negatively charged toner sticks to the charged areas, then is transferred to paper and heated to fix it.

How does an insecticide sprayer use static electricity?

The insecticide droplets are given the same electrostatic charge as they leave the sprayer, so they repel each other and form a fine mist that covers a large area.

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