Chapter 5 PartC

8/6/2019 Chapter 5 PartC

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Chapter 5 Electricity and Magnetism

Part III

Chapter 5 Electricity and Magnetism

Part III

Sherry YinSherry Yin



Ohm¶s Law

Ohm¶s Law

Ohm¶s law gives the relation between

voltage, current and resistance.

According to Ohm, current in a circuit is

directly proportional to the applied voltage

and inversely proportional to the resistance

of the conductor.

Ohm¶s law gives the relation between

voltage, current and resistance.

According to Ohm, current in a circuit is

directly proportional to the applied voltage

and inversely proportional to the resistance

of the conductor.

R !

V

I



Electric Potential &

Electric Potential Energy

Electric Potential &

Electric Potential Energy

Electric potential energy has a dependency

upon the charge of the object and theelectric field itself.

The concept of electric potential is used to

express the affect of an electric field of asource in terms of the location within the

electric field.

Electric potential is purely location dependent.

Electric p

otential energy has a dependency

upon the charge of the object and theelectric field itself.

The concept of electric potential is used to

express the affect of an electric field of asource in terms of the location within the

electric field.

Electric potential is purely location dependent.



Electric PotentialElectric Potential

A test charge with twice the quantity of charge would possess twice the potential energy at a given location; yetits electric potential at that locationwould be the same as any other test

charge.

A test charge with twice the quantity of charge would possess twice the potential energy at a given location; yetits electric potential at that locationwould be the same as any other test

charge.

Electric potential is the

amount of potential

energy per unit of charge.



Electric Potential differenceElectric Potential difference

A battery powered electric circuit

has locations of high and low

potential.

There must be a potential difference between the electrodes to make

charges flow.

This difference in electric potential

is represented by the symbol V andis formally referred to as the electric

potential difference.

A battery powered electric circuit

has locations of high and low

potential.

There must be a potential difference between the electrodes to make

charges flow.

This difference in electric potential

is represented by the symbol V andis formally referred to as the electric

potential difference.



Unit of Electric Potential difference

Unit of Electric Potential difference

Unit: volt, abbreviated V

and named in honor of

Alessandro Volta.

Because electric potential

difference is expressed in

units of volts, it issometimes referred to as

the voltage.

Unit: volt, abbreviated V

and named in honor of

Alessandro Volta.

Because electric potential

difference is expressed in

units of volts, it issometimes referred to as

the voltage

. RV

I



Electric CurrentElectric Current

This potential difference creates an electricfield

Free charges inside this electric field are

exerted a force Under the effects of this force, electrical

charges starts to flow.

This flow of charge is called electriccurrent.

If there is no potential difference then therewon¶t be flow of charge or electric current.

This potential difference creates an electricfield

Free charges inside this electric field are

exerted a force Under the effects of this force, electrical

charges starts to flow.

This flow of charge is called electriccurrent.

If there is no potential difference then therewon¶t be flow of charge or electric current.



Electric CurrentElectric Current

R !

V

I

Unit: Ampere (A). (Coulomb per second)

Named after André-Marie Ampère

Unit: Ampere (A). (Coulomb per second)

Named after André-Marie Ampère



Conductor Conductor

Free charges inside this electric field are exerted a force

Conductors are materials that permit electrons toflow freely from atom to atom and molecule to

molecule. An object made of a conducting material will

permit charge to be transferred across the entire

surface of the object. The distribution of charge is the result of electron

movement.

Free charges inside this electric field are exerted a force

Conductors are materials that permit electrons toflow freely from atom to atom and molecule to

molecule. An object made of a conducting material will

permit charge to be transferred across the entire

surface of the object. The distribution of charge is the result of electron

movement.



Conductor Conductor Examples of conductors include metals,

aqueous solutions of salts, graphite, water

and the human body.

Of the metals commonly used for conductors,

copper has a high conductivity. Silver is more

conductive, but due to cost it is not practicalin most cases. However, it is used in

specialized equipment, such as satellites.

Examples of conductors include metals,

aqueous solutions of salts, graphite, water

and the human body.

Of the metals commonly used for conductors,

copper has a high conductivity. Silver is more

conductive, but due to cost it is not practicalin most cases. However, it is used in

specialized equipment, such as satellites.



Insulator Insulator

In contrast to conductors, insulators arematerials that impede the free flow of electrons from atom to atom and molecule

to molecule. If charge is transferred to an insulator at a

given location, the excess charge will

remain at the initial location of charging. Examples of insulators include plastics,

Styrofoam, paper, rubber, glass and dry air.

In contrast to conductors, insulators arematerials that impede the free flow of electrons from atom to atom and molecule

to molecule. If charge is transferred to an insulator at a

given location, the excess charge will

remain at the initial location of charging. Examples of insulators include plastics,

Styrofoam, paper, rubber, glass and dry air.



Conductor and Insulator Conductor and Insulator



R esistance

R esistance

An electron traveling through the wires and

loads of the external circuit encounters

resistance. R esistance is the hindrance to

the flow of charge.

While the electric potential difference

encourages the movement of charge, it isresistance that discourages it.

An electron traveling through the wires and

loads of the external circuit encounters

resistance. R esistance is the hindrance to

the flow of charge.

While the electric potential difference

encourages the movement of charge, it isresistance that discourages it.



R esistanceR esistance

First, which material the substance is made of

Second, the total length of the substance will

affect the amount of resistance. The longer it is, the more resistance that there will

be.

Third, the cross-sectional area of the object will

affect the amount of resistance. The wider it is, the less resistance that there will be.

First, which material the substance is made of

Second, the total length of the substance will

affect the amount of resistance. The longer it is, the more resistance that there will

be.

Third, the cross-sectional area of the object will

affect the amount of resistance. The wider it is, the less resistance that there will be.



R esistance

R esistance

Unit: ohm ();

named after Georg SimonOhm

Unit: ohm ();

named after Georg SimonOhm

R !

V

I

Resistance is represented withthe following picture in circuits;



ExerciseExercise

Determine the current that flows through a 30

ohm resistor that has a potential difference

(voltage) of 120 v.

Determine the current that flows through a 30

ohm resistor that has a potential difference

(voltage) of 120 v.



Something sweetSomething sweet



Something Cute~~Something Cute~~

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Chapter 5 PartC