ElectrostaticsElectrostaticsthe study of electrical

charges at rest

ElectrodynamicsElectrodynamicsthe study of electrical

charges in motion

Two oppositeopposite types of charge exist, named positivepositive and negativenegative by Benjamin Franklin.

Charge is aproperty of

matter.

Charged particlesCharged particles exist in atoms. exist in atoms.

ElectronsElectrons are responsible are responsiblefor for negativenegative charge; charge;

protonsprotons for for positivepositive charge; charge;neutronsneutrons have have nono charge. charge.

Small amountsSmall amounts of ordinary matter contain of ordinary matter containincredible amountsincredible amounts of subatomic particles! of subatomic particles!

Choose an element on the periodic table.Choose an element on the periodic table.

Iron has Iron has atomic numberatomic number of 26. This means that of 26. This means that there are there are 26 protons26 protons in each atom of iron. in each atom of iron.

Assuming that the iron atom is Assuming that the iron atom is neutral neutral (no net (no net charge), the atom will also have charge), the atom will also have 26 electrons26 electrons..

The number below the element is the The number below the element is the atomic massatomic mass. This number tells us . This number tells us that on average, each atom of iron has a total of 55.845 protons and that on average, each atom of iron has a total of 55.845 protons and neutrons in the nucleus. Since there are exactly 26 protons in an atom neutrons in the nucleus. Since there are exactly 26 protons in an atom of iron, on average each iron atom has 29.845 neutrons.of iron, on average each iron atom has 29.845 neutrons.

How is that possible? The number of neutrons in the iron atom can How is that possible? The number of neutrons in the iron atom can vary. Some vary. Some isotopesisotopes of iron contain exactly 29 neutrons, some have 28, of iron contain exactly 29 neutrons, some have 28, and some have 30. and some have 30.

Different Different isotopesisotopes of iron may be expressed as Fe-55, Fe-56, Fe-57, etc... of iron may be expressed as Fe-55, Fe-56, Fe-57, etc...

The atomic mass also tells us the mass in grams of one The atomic mass also tells us the mass in grams of one molemole of iron. of iron.

Charged atoms are known as Charged atoms are known as ionsions..

An atom becomes charged by gaining or losing An atom becomes charged by gaining or losing electronselectrons. .

The charge of an ion is typically expressed as an The charge of an ion is typically expressed as an exponent written after the atomic symbol.exponent written after the atomic symbol.

CuCu+2+2 represents a copper atom with a +2 charge, represents a copper atom with a +2 charge, which means that it is a copper atom that which means that it is a copper atom that lost 2 lost 2 electronselectrons..

CuCu-1-1 represents a copper atom with a -1 charge, represents a copper atom with a -1 charge, which means that it is a copper atom that which means that it is a copper atom that gained gained an electronan electron..

Let’s count the number of subatomic Let’s count the number of subatomic particles (protons, neutrons, and electrons) particles (protons, neutrons, and electrons) in a relatively small amount of an element.in a relatively small amount of an element.

Let’s assume that a penny is pure copper and has a mass of 3.4 grams. Checking the periodic table, we find that the atomic number of copper is 29 and its atomic mass is 63.546.

This means that 6.022 x 1023 atoms of copper (= 1 mole = Avogadro’s number) has a mass of 63.546 grams, and each individual atom contains 29 protons, 29 electrons, and on average, 34.546 neutrons.

Therefore, the number of copper atoms in a 3.4 gram penny is found by multiplying Avogadro’s number by 3.4/63.546. This value is then multiplied by 29 and 34.546 to determine the approximate numbers of subatomic particles in the penny.

How long would it take to count them????????

ConductorConductormaterial that allows charges to move about easily

InsulatorInsulatormaterial through which charges will not easily move

Like charges repel; unlike charges attractLike charges repel; unlike charges attract

Basic Law of Electrostatics:Basic Law of Electrostatics:

Click Click here to read about charging objects to read about charging objects by contact (friction). See shoes on carpet by contact (friction). See shoes on carpet here. See a balloon on your sweater . See a balloon on your sweater here..

View a simulationView a simulationof charging aof charging aballoon by rubbing balloon by rubbing it on your hair it on your hair and then stickingand then stickingit to a neutralit to a neutralwall wall here. .

The SI unit of chargeThe SI unit of chargeis the is the CoulombCoulomb,,

named in honor ofnamed in honor ofCharles Augustin Coulomb..

1 C = charge on 1 C = charge on 6.25 x 106.25 x 101818 electrons (or protons) electrons (or protons)

1 e1 e-- = = 1.60 x 101.60 x 10-19-19 CoulCoul = elementary charge = elementary charge

How many Coulombs of negative charge are How many Coulombs of negative charge are contained in that copper penny? contained in that copper penny?

COULOMB’S LAWCOULOMB’S LAWThe force between two charged objects isThe force between two charged objects isdirectly proportional to the product of theirdirectly proportional to the product of theircharges and inversely proportional to theircharges and inversely proportional to their

separation distance squared.separation distance squared.

link1, link2, link3, link4, link4

In equation form:In equation form:

FFF is the is the force of attractionforce of attraction, measured in , measured in NEWTONSNEWTONS,,between charges qbetween charges q11 and q and q22

k

kk is the is the Universal Electrostatic ConstantUniversal Electrostatic Constant, equal to , equal to

9.00 x 109.00 x 1099 N N mm22/coul/coul22

q1q2

qq11 and and qq22 are the are the attracting chargesattracting charges, measured in, measured inCoulombsCoulombs

d2

dd is the is the distance between the chargesdistance between the charges, , and is measured in and is measured in METERSMETERS

Electric FieldsElectric FieldsAn electric field exists in a regionAn electric field exists in a regionif space if a charge placed in thatif space if a charge placed in that

region experiences an electric force.region experiences an electric force.

The magnitude of an electric field at any The magnitude of an electric field at any given point is defined to be the ratio ofgiven point is defined to be the ratio ofthe force on athe force on acharge at thatcharge at thatpoint to the point to the amount of charge.amount of charge.

E = F/QElectric field strength has unitsElectric field strength has units

of Newtons/Coulomb (N/C).of Newtons/Coulomb (N/C).

The The directiondirection of the electric fieldof the electric field at any point is defined at any point is definedto be the same direction as the to be the same direction as the direction of force on a direction of force on a positive test chargepositive test charge placed in the region at that point. placed in the region at that point.

Field lines point Field lines point awayaway from positive from positive charges and charges and towardtoward negative charges.negative charges.

Investigate electric fields Investigate electric fields due to point charges due to point charges

at the simulation here.at the simulation here.

Click here to view a Click here to view a simulation showing the simulation showing the magnitude and direction magnitude and direction of the electric force on a of the electric force on a test charge when placed test charge when placed near other charges.near other charges.

Click here to view a Click here to view a simulation of a charged simulation of a charged particle moving through particle moving through

a region occupied by a region occupied by other charges.other charges.

Electric Potential DifferenceElectric Potential Difference

the change in the change in electric potential energyelectric potential energyper unit chargeper unit charge V = W/Q

The SI unit of electric potentialdifference is the VOLTVOLT, named in

honor of Alessandro VoltaAlessandro Volta.

One One VOLT VOLT is the is the electric potential electric potential difference difference between two points when between two points when one Jouleone Joule

of work is done in moving of work is done in moving one Coulombone Coulomb of charge between the points.of charge between the points.