Electric CurrentElectric Current The amount of charge that moves past a The amount of charge that moves past a

given point in a conductor per second.given point in a conductor per second. I = I = qq

tt

I = current (amperes)I = current (amperes) q = quantity of charge q = quantity of charge

(coulombs)(coulombs)

t = time (seconds)t = time (seconds)

Ampere is the amount of current when Ampere is the amount of current when one coulomb of charge moves by a point one coulomb of charge moves by a point in a conductor in one second.in a conductor in one second.

Calculate the amount of current Calculate the amount of current through a toaster if it takes 900 through a toaster if it takes 900 coulombs of charge to toast two coulombs of charge to toast two slices of bread in 1.5 minutes.slices of bread in 1.5 minutes. Given Given

t = 1.5 minutes = 90 secondst = 1.5 minutes = 90 seconds

q = 900 coulombsq = 900 coulombs

qq = I = I 900 Coulombs900 Coulombs = 10 C/s or = 10 C/s or ampsamps

t 90 secondst 90 seconds

Measuring devicesMeasuring devices

Electric PotentialElectric Potential When charges are in the presence of an When charges are in the presence of an

electric field they have potential electric field they have potential energy.energy. The charges position in the electric field The charges position in the electric field

determines how much potential energy determines how much potential energy that charge will have.that charge will have.

Remember like charges repel and opposite Remember like charges repel and opposite charges attract.charges attract.

Two charges will have potential energy between Two charges will have potential energy between them just like objects possess potential energy them just like objects possess potential energy when they are raised above the earth’s surface.when they are raised above the earth’s surface.

Potential Difference and Potential Difference and VoltageVoltage

Moving charges in an electric field Moving charges in an electric field requires work.requires work.

Voltage is the potential difference.Voltage is the potential difference. Voltage = Voltage = workwork (change in potential energy)(change in potential energy)

chargecharge

Joules/Coulomb = VoltJoules/Coulomb = Volt

One volt is the electric potential One volt is the electric potential difference between two points if it difference between two points if it takes 1 Joule of work per coulomb to takes 1 Joule of work per coulomb to move a positive charge from one move a positive charge from one pointpoint to another.to another.

1 volt = 1 Joule per coulomb1 volt = 1 Joule per coulomb A 12 volt battery means that 12 Joules of work is A 12 volt battery means that 12 Joules of work is

done on each Coulomb of charge that flows done on each Coulomb of charge that flows through it.through it.

As charges flow through conductors As charges flow through conductors they lose potential energy.they lose potential energy.

The electrical energy lost or work done by The electrical energy lost or work done by a charge traveling through a conductor a charge traveling through a conductor can be calculated.can be calculated.

E = qV like E = qV like ΔΔPEg = PEg = ΔΔmghmgh E = energy lost or change in energy. (Joules)E = energy lost or change in energy. (Joules) q = charge (Coulombs)q = charge (Coulombs) V = potential difference (voltage)V = potential difference (voltage)

q =It substituting It for q in E =qVq =It substituting It for q in E =qV E = ItVE = ItV

E = energy lost (Joules)E = energy lost (Joules) I = current (amperes)I = current (amperes) t =time (seconds)t =time (seconds) V = voltage (volts)V = voltage (volts)

Sources of CurrentSources of Current BatteriesBatteries

Provide a source of electrons through a Provide a source of electrons through a chemical reaction.chemical reaction.

Voltaic Cells Voltaic Cells Two metal strips called electrodes create ions Two metal strips called electrodes create ions

when submerged in acid (electrolyte)when submerged in acid (electrolyte) Since they are two different metals a deficit of Since they are two different metals a deficit of

electrons is created at one electrode and a electrons is created at one electrode and a surplus of electrons is created at the other surplus of electrons is created at the other electrode.electrode.

When these terminals are connected by a When these terminals are connected by a wire, the electrons flow from one electrode to wire, the electrons flow from one electrode to the other.the other.

BatteriesBatteries Dry cells (Duracell, Energizer etc..)Dry cells (Duracell, Energizer etc..)

Two electrodes are used, carbon and zinc, Two electrodes are used, carbon and zinc, in a moist paste of ammonium chloride in a moist paste of ammonium chloride (electrolyte).(electrolyte).

Easier to handleEasier to handle Create 1.5 VoltsCreate 1.5 Volts Can connect several together to increase Can connect several together to increase

the voltage.the voltage. Problem with voltaic and dry cell Problem with voltaic and dry cell

batteries is when the electrolyte is batteries is when the electrolyte is used up the battery no longer used up the battery no longer functions.functions.

SolutionSolution

Secondary or rechargeable batteriesSecondary or rechargeable batteries The chemical mixture used can be The chemical mixture used can be

reversed when current is applied.reversed when current is applied. The chemical reactants are restored.The chemical reactants are restored. Nickel and cadmium are commonly used Nickel and cadmium are commonly used

in toysin toys

ElectromagnetsElectromagnets Electromagnetic generatorsElectromagnetic generators

Moving a wire through and electric field Moving a wire through and electric field generates current.generates current.

Called electromagnetic induction.Called electromagnetic induction. Powered by water, nuclear plants, Powered by water, nuclear plants,

geothermal steam or burning coal.geothermal steam or burning coal.

Other Sources of CurrentOther Sources of Current PiezoelctricityPiezoelctricity

Pressing on piezoelectric material induces small Pressing on piezoelectric material induces small charges.charges.

Phonograph needles connected to a piezoelectric crystal Phonograph needles connected to a piezoelectric crystal pick up vibrations due the grooves in a record and theses pick up vibrations due the grooves in a record and theses vibrations are amplified.vibrations are amplified.

ThermocouplingThermocoupling A device that uses different metals attached to a loop of A device that uses different metals attached to a loop of

wire to create electrcity when heated.wire to create electrcity when heated. PhotoelectricityPhotoelectricity

The photoelectric effect. Einstein used light to cause The photoelectric effect. Einstein used light to cause metals to release electrons.metals to release electrons.

Solar cellsSolar cells Semiconductors with a “wafer like” material is treated to Semiconductors with a “wafer like” material is treated to

form a junction. When the junction is exposed to light a form a junction. When the junction is exposed to light a small electric potential difference is created.small electric potential difference is created.

In order for current to flow through a In order for current to flow through a conductor there must be a electrical conductor there must be a electrical potential difference or voltage potential difference or voltage present.present.

This difference in potential causes This difference in potential causes charges to flow from a high electric charges to flow from a high electric potential to a lower electric potential.potential to a lower electric potential.

The amount of current that flows The amount of current that flows through a conductor depends on the through a conductor depends on the voltage and the material in which the voltage and the material in which the conductor is made of.conductor is made of.

Ohm’s LawOhm’s Law Relates current, voltage and resistance.Relates current, voltage and resistance.

VV = = II RR V= voltage (volts)V= voltage (volts)R = resistance R = resistance

(ohms)(ohms)

I = current I = current (amperes)(amperes)

ResistanceResistance Property of a material that inhibits the flow Property of a material that inhibits the flow

of charge.of charge.

ResistanceResistance Factors that affect the resistance of a Factors that affect the resistance of a

conductor:conductor: Length of the wireLength of the wire

Longer wires pose more resistance than shorter ones.Longer wires pose more resistance than shorter ones. Width of the wireWidth of the wire

Narrow wires introduce more resistance than wider Narrow wires introduce more resistance than wider wires.wires.

Composition of the materialComposition of the material TemperatureTemperature

Higher temperatures introduce more resistance than Higher temperatures introduce more resistance than lower temperatures.lower temperatures.

Electric PowerElectric Power The rate at which electrical potential The rate at which electrical potential

is converted to other types of energy.is converted to other types of energy. Electric to light energy - light bulbElectric to light energy - light bulb Electric to mechanical energy – motorElectric to mechanical energy – motor

Power = Current x VoltagePower = Current x Voltage P = IV P = IV

P = power (watts)P = power (watts)

I = current (amperes)I = current (amperes)

V = voltage (volts)V = voltage (volts)

Voltmeters must always be Voltmeters must always be connected in parallelconnected in parallel

Ammeters must always be Ammeters must always be connect in seriesconnect in series