8.3.1-Electricity

Chapter 3
Electricity

1. How do electrically charged objects interact?

2. How can objects become electrically charged?

3. What is an electric discharge?

Essential Questions

Lesson 3.1: Electric Charge & Electric Forces

What is Electricity?

• Electricity is the flow of electrical power or charge.

• It is a secondary energy source which means that we get it from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which are called primary sources.

Where does electricity come from?

• It comes from the flow of electrons in atoms.

• Electrons are negatively charged subatomic particles.

Multiple Choice

What are electrons?

• Positively charged subatomic particles

• Negatively charged subatomic particles

• Neutral subatomic particles

Multiple Choice

Electricity is caused by the flow of electrons in atoms.

• True

• False

Static Electricity

• The build up of an electric charge

  on the surface of an object.

• Static electricity is potential energy

  because it does not move.

Multiple Choice

Static electricity is...

• potential energy

• kinetic energy

Static Discharge

• Occurs when there is a loss of static

  electricity due to three possible

  things:

• Friction - rubbing

  
  

  Conduction – direct contact

  
  

  Induction – through an electrical

  field (indirect contact)

Electric charge

is produced when there is imbalanced number in electrons or protons

is this particle electrically charge?

Types of Charges

• All atoms contain small particles called Electrons and Protons

  • Electrons have a Negative Charge

  • Protons have a Positive Charge

• Charges always interact the same way

  • Similar charges repel each other

  • Opposite Charges Attract each other

What is Electric Force?

• Electricity: the interaction between electric charges

• Electric Force: The force that occurs between charged objects

  • Can act at a distance

Types of Charges

• All atoms contain small particles called Electrons and Protons

  • Electrons have a Negative Charge

  • Protons have a Positive Charge

• Charges always interact the same way

  • Similar charges repel each other

  • Opposite Charges Attract each other

Multiple Choice

What are the positively charged particles in an atom?

• protons

• neutrons

• electrons

• isotopes

Multiple Choice

What are the negatively charged particles in an atom?

• protons

• neutrons

• electrons

• isotopes

Multiple Choice

What are the neutral particles in an atom?

• protons

• neutrons

• electrons

• isotopes

Multiple Choice

What type of charge do normal atoms have?

• positive

• negative

• neutral

• None of the above

Multiple Choice

How can we make an atom positive?

• Adding an electron

• taking away an electron

• adding a proton

• taking away a proton

Multiple Choice

How can we make an atom negative?

• Adding an electron

• taking away an electron

• adding a proton

• taking away a proton

Multiple Choice

What do we call it when two objects rub together?

• friction

• conduction

• induction

• electroscope

Multiple Choice

What is it called when a charged object induces a charge onto a neutral object without direct contact?

• friction

• conduction

• induction

• electroscope

Multiple Choice

What is it called when electrons are transferred by direct contact?

• friction

• conduction

• induction

• electroscope

Multiple Choice

What instrument detects an electric charge?

• friction

• conduction

• induction

• electroscope

What is an Electric Charge?

​A Property of Matter

All matter is made of particles that are too small to see. Some of these particles have electric charge.

An Electric charge is a property of matter that causes electrical phenomena. Particles with electric charge interact with other particles with electric charge.

Something that has a negative charge has more particles with a negative charge than particles that are positively charged.

​Negative

Something that has a positive charge has more particles with a positive charge than particles that are negatively charged.

​Positive

Two Kinds of Electric Charge

objects may have either equal or unequal numbers of positively charged particles and negatively charged particles.

when you rub a balloon on your hair, negatively charged particles from your hair are transferred to the balloon. Your hair now has more positively charged particles than negatively charged particles, and has an overall positive charge.

​​What is a Positive Charge?

​The balloon, on the other hand, has more negatively charged particles and has an overall negative charge.

​​What is a Negative Charge?

Poll

Electric charges surround you all the time. Some electric charges, such as lightning, are quite strong. Others are barely noticeable. What happens when two electrically charged objects get near each other?

• The two objects will be pulled toward each other

• The two objects will be pushed away from each other

• The two objects will either be pulled together or pushed apart

• The charges will cancel out and neither object will move toward or away from the other

Why does the balloon attract the water?

BEND WATER – WITH YOUR HAIR?

BEND WATER – WITH YOUR HAIR?

When you rub a balloon on your head electrons move from your head to the balloon. This causes the balloon to be negatively charged and your head to be positively charged. Because opposite charges attract each other, the balloon will now stick to your head as well as other things such as a wall. It can also cause a stream of water to bend.

Multiple Choice

What happens when you rub a balloon on your hair?

• The balloon to be negatively charged.

  Your head to be positively charged.

• The balloon to be positively charged.

  Your head to be negatively charged.

Multiple Choice

The water stream will be attracted to the balloon because:

• The balloon is positively charged, while the water stream will be negatively charged.

• The balloon is negatively charged, while the water stream will be positively charged.

Conclusion

So, just like the magnetic force:

Like charges tend to repel.

Opposite charges tend to attract.

Multiple Choice

If you bring two positive charges near each other, what will happen?

• The two charges will repel from each other

• The two charges will attract each other

Multiple Choice

If you bring two negative charges near each other, what will happen?

• The two charges will repel from each other

• The two charges will attract each other

Multiple Choice

If you bring a negative charge and a positive charge near each other, what will happen?

• The two charges will repel from each other

• The two charges will attract each other

Multiple Choice

Electric charges surround you all the time. Some electric charges, such as lightning, are quite strong. Others are barely noticeable. What happens when two electrically charged objects get near each other?

• The two objects will be pulled toward each other

• The two objects will be pushed away from each other

• The two objects will either be pulled together or pushed apart

• The charges will cancel out and neither object will move toward or away from the other

Multiple Choice

) When an object has more negative charge than positive charge, the object is called _____.

• A) electric discharge

• B) magnetic domain

• C) electric field

• D) electrically charged

Multiple Choice

An object with equal amounts of positive and negative charge is electrically _____.

• A) charged

• B) negative

• C) neutral

• D) positive

​Induction

is the charging of an object without touching it.

conduction

Transfer of charged partciles between two conductors is conduction.

Multiple Choice

Normally, materials are electrically neutral because there are ____.

• A) more positively charged particles than negatively charged particles

• B) more negatively charged particles than positively charged particles

• C) equal numbers of positively charged particles and neutrally charged particles

• D) equal numbers of positively charged particles and negatively charged particles

Multiple Choice

A material through which electrons can move easily is a _____.

• A) conductor

• B) charge

• C) insulator

• D) magnet

Multiple Choice

Each of the following is an example of an insulator EXCEPT _____.

• A) copper

• B) glass

• C) rubber

• D) wood

Multiple Select

Sub-atomic particle with charges

• Volts

• Proton

• Electron

Multiple Select

These subatomic particles are (blank) but are found stationary in the (blank) of the atom

• Negative

• Electron

• Positive

• Nucleus

Multiple Choice

A rubber ball is dropped and bounces back up. The ball has __________.

• zero potential energy at A

• zero kinetic energy at C

• both kinetic and potential energy at A

• both kinetic and potential energy at C

Multiple Choice

A rubber ball is dropped and bounces back up. The ball's potential energy _______.

• is greater at C than at A

• is the same as its kinetic energy at A

• is at its maximum at A

• is zero at B

Multiple Choice

In which diagram does the ball have the greatest potential energy?

• A

• B

• C

• D

Multiple Choice

Which of the following shows that opposite charges attract?

What determines the strength of an electric field?

• the total amount of charge on both objects and the distance between the objects

• the more the charge, the stronger the force in the field

• the larger the distance, the weaker the force in the field​

Multiple Choice

An electric field gets stronger as you ____.

• get closer to a charge

• get farther from a charge

• add negatively charged particles to a positively charged object

• remove negatively charged particles from a negatively charged object

Method of charging an object without touching it

​​Induction

• ​Material in which charges cannot easily flow.

• examples: glass, rubber, wood, and air​

​​Electric Insulators

• ​material in which electric charge can easily move

• examples: metals like copper and aluminium​

Electric Conductors

​How do different materials hold charges?

• another way that charged particles transfer between two conductors

• conducting objects with unequal charges touch

• charged particles flow from the object with more negative charge to the object with less negative charge

​​Conduction

​

​How do different materials hold charges?

Multiple Choice

An object with equal amounts of positive and negative charge is electrically _____.

• charged

• negative

• neutral

• positive

Multiple Choice

Each of the following is an example of an insulator EXCEPT _____.

• copper

• glass

• rubber

• wood

Multiple Choice

A material through which electrons can move easily is a _____.

• conductor

• charge

• insulator

• magnet

Poll

How well do you understand electric forces?

• I get it!

• I kind of understand.

• I still have questions.

• I don't understand.

How does Charge Build up?

• Most objects have no overall charge

  • Has the same number of Protons and Electrons

  • Neutral

• An object can become charged by gaining or losing electrons

  • If an object loses electrons, it becomes more positively charged

  • If an object gains electrons, it becomes more negatively charged

How does Charge Build up?

• Static Electricity: the build-up of charge on an object

  • Charges do not flow continuously but slowly collect in an object

Charging Objects

• Law of Conservation of Charge: Charges are not created nor destroyed, only transferred from one object to another

• There are four ways an object can gain or lose charge

  • Friction

  • Conduction

  • Induction

  • Polarization

Charging By Friction

• Involves two uncharged objects rubbing against each other

  • As the objects are moved, electrons can be moved from one object to another

Charging By Conduction

• Electrons are transferred from a charged object to another object through direct touching

  • Electrons move toward an area with a more positive charge

Charging By Induction

• Electrons can react to the electric field of a charged object without touching the object itself

• Metals tend to lose electrons very easily

• Induction: When the electrons in a metal object react to an electrical field, and make an object have a positive and a negative end

  • Can produce a spark

Charging By Polarization

• Sometimes Electrons do not move between atoms, but rotate in their atoms

  • Electrons move so they are on one end of an atom

• Polarization: The process of individual atoms gaining a positive and negative charge on their ends

  • Does not involve transfer between objects

  • Overall the object remains neutral

Static Discharge

• Once charged, an object will slowly change to become neutral

  • Negatively charged objects will lose electrons

  • Positively charged objects will gain electrons

• Static Discharge: The loss of Static Electricity as electric charges transfer from one object to another

  • Often produces a spark from electrons heating the air

  • More common in dry weather because water is not in the air to attract charges

Static Discharge

• Lighting is static discharge in action

  • During storms, air particles move inside clouds and become charged

  • As the electrons move from areas that are negatively charged to areas that are positively charged and produce a spark

  • When charges form a negative electric field, the Earth becomes more positively charged, which can allow lightning to jump from clouds to the Earth's surface

Lightning:

Lightning is an electric discharge or an electric spark that occurs in nature on a major scale.

It is caused by the accumulation of charges in the clouds.

It can be deadly and cause the destruction of life and property.

In ancient times people were unaware of the cause of lightning and hence they were scared of it.

Nowadays, scientists have evolved some precautions that can help us prepare and protect ourselves from this natural phenomenon.

The sparks that Greeks knew about:

The Greeks were already aware of the electric charges from 600 BC. They knew that when Amber (a type of resin or synthetic polymer) and fur are rubbed together, then amber can attract light objects like hair. Similarly, woollen clothes or polyester clothes also attract hair and can produce a little spark or crackling sound when they are taken off from the body. This is because of electric charges. Benjamin Franklin was an American scientist who in 1752 discovered and proved that lightning and spark produced from these clothes are all same things.

What are electric charges?

We know that every atom comprises of subatomic particles such as electrons, protons and neutrons.

All these particles share a common property that they carry electric charges.

What are electric charges?

Electrons have a negative charge on them while protons have a positive charge.

We know that atoms carry a balanced charge however these charges may sometimes become out of order.

An object will be called electrically neutral if it is carrying a balanced proportion of positive and negative charges.

An object is called a charged object if there is an imbalance of electrons and protons in it.

Charging by rubbing:

When we rub two objects with each other they get charged due to a transfer of electrons between them.

For example, if we rub a rubber balloon with animal fur, the balloon is made up of rubber attracts the electrons from the animal fur.

This results in rubber having an excess of electrons while fur having a shortage of electrons.

In the same way, if we rub a plastic comb with dry hair the comb acquires some charge.

Types of charges and their interaction:

We know that charged objects may have a shortage or excess of electrons.

Objects having an excess of electrons are called negatively charged while an object having a shortage of electrons are called positively charged.

Types of charges and their interaction:

For instance, when a glass rod is rubbed with silk cloth it becomes positively charged while the silk cloth becomes negatively charged. These charged objects are now capable of attracting other charged and uncharged objects. Objects having the same kind of charges repel each other while objects with different kind of charges attract each other.

Static Charges when woollen sweater and balloon are rubbed together

Transfer of charges:

Charges can transfer from one object to another with the help of conduction and induction:

Conduction:

when a charged object comes in contact with a conductor it results in the transfer of charges through the conductor.

Induction:

When a charged object is brought near a neutral object, it results in shifting in the position of the electrons in the other object.

The process of induction does not involve any physical contact between the charged and uncharged object while the process of conduction requires a physical contact between them.

How the transfer of electric charges leads to conservation of charge?

The net charge on a neutral object is zero. However, when an object receives some electrons from another object, the net negative charge on the first object is equal to the net positive charge of the second object. In this way, charges are conserved during transfer of charges. 

What is an electroscope?

It is a device which can test if an object is charged or not. Abraham Bennet developed a gold leaf electroscope in 1787.

Structure of an electroscope:

Generally, gold and silver are used to construct an electroscope because they are good conductors of electricity.

Otherwise, copper and aluminium can also be used.

It consists of a glass jar having a vertical brass rod.

The rod is inserted into the jar through the cork.

The brass rod has a brass disc or horizontal rod attached to it.

From the other end, two leaves of gold are suspended.

Working of an electroscope:

When a charged object touches the brass disc, electric charges get transferred from the brass rod to the gold leaves. As a result, the gold leaves move away from each other depicting the presence of charges.

Discharging and Earthing;

When a charged object loses its charges it is said to be discharged.

When a charged object transfers its charges to the earth it is called earthing.

Generally, every building is provided with earthing to protect it from electrical shocks due to leakage of electric current.

How Earthing Protects us form Shock

How Can we get a Shock Without Earthing

Story of Lightning:

During a thunderstorm, the hot air moves upwards while the raindrops fall downloads.

This leads to a separation of charges in the atmosphere.

As a result, negative charges get accumulated in the lower ages of the clouds while positive charges accumulate at the upper edges.

Story of Lightning:

The ground is accumulated with a positive charge all over.

These charges begin to multiply due to the increase in winds and rainfall.

Although the air is a poor conductor of electricity due to heavy charges it is unable to restrict the electric flow after some time.

Story of Lightning:

The negative charges and positive charges meet which results in the production of electric sparks in the form of a streak of light accompanied by a sound.

The streak is called lightning and the whole phenomenon is called electric discharge.

This electric discharge can occur between two or more clouds.

Why does lightning strikes tall buildings easily?

We know that lightning occurs as a streak of charges that fall toward the ground.

Tall buildings and tall trees can easily conduct the charge towards the ground.

The air gap between these buildings and lightning is short hence they are more susceptible to lightning.

That does not mean that short objects would not be affected by lightning. 

Lightning safety:

One should not stay at an open place during lightning and thunderstorm.

Hence as soon as we hear any alert about lightning or thunderstorm, we should rush to a safe place such as a house or a building.

If somebody is there in a car or bus, they should stay inside and keep all the doors and windows closed.

One should read inside the safe place until the storm lasts.

Do's and don'ts for lightning safety:

Outdoor Safety

One should not stay in an open place such as an open vehicle like a motorbike, tractor, or open fields, elevated places, or tall trees.

One should not carry an umbrella during the storm.

If a person is around a forest they should hide under short trees.

One should not get near to any poles on metal objects.

One should squat low on the ground instead of laying down.

Lightning Safety

Indoor Safety:

Lightning is an electric discharge hence one should stay away from electrical wires telephone, cables and metal pipes during a thunderstorm.

One may use a cordless phone or a mobile phone in an emergency.

One should not come in contact with the running water hence one should avoid bathing.

One should unplug all the electrical appliances in the house, for example TV, computers or music systems.

Electrical lights do not cause any harm and hence can be kept on.

Lightning Safety

Using a lightning conductor:

In order to protect buildings from lightning, a lightning conductor device is used.

When the building is being constructed a metallic rod having height more than the building is placed in the walls of the building.

One end of the rod is in the air while the other end is buried inside the Earth.

This rod is a conductor and hence during lightning it allows the flow of electric charges to the ground.

Lightning Conductor

Working of a lightning conductor:

The lightning conductor rod consists of pointed ends which are made up of copper wire.

These copper wires are brought down along the building and are attached to a metallic plate in the ground.

If lightning hits the building the copper wires carry these charges quickly to the ground.