Current Current ElectricityElectricity

How is current How is current produced?produced? When a high potential is When a high potential is

connected by a conductive connected by a conductive material to a low potential. material to a low potential.

– Flow of electrons is called electric Flow of electrons is called electric current.current.

– Units: C/s = Amperes (Amps)Units: C/s = Amperes (Amps) t

qI

High Potential

Low Potential Equal

PotentialEqual Potential

When the potentials are equal, When the potentials are equal, the current stops flowing the current stops flowing – To increase the potential of the To increase the potential of the

electrons an electron pump must electrons an electron pump must convert (do work) another form of convert (do work) another form of energy into electrical potential energy into electrical potential energy.energy. Electron pump examples: Electron pump examples:

– Voltaic or galvanic cell (dry cell)Voltaic or galvanic cell (dry cell)– Several cells connected (Battery)Several cells connected (Battery)– Photovoltaic cell (solar cell)Photovoltaic cell (solar cell)– GeneratorGenerator

High Potential

Low Potential

Electron Pump

Two types of current Two types of current

Direct Current – (D.C.) Flow of Direct Current – (D.C.) Flow of electrons in only one directionelectrons in only one direction

– BatteryBattery Alternating Current – (A.C.) Flow of Alternating Current – (A.C.) Flow of

electrons at first in one direction and electrons at first in one direction and then the other direction. then the other direction.

– GeneratorGenerator– In your HouseIn your House– 60 Hertz60 Hertz

What affects current What affects current flow?flow? Potential Difference – VoltagePotential Difference – Voltage Resistance - slowing or Resistance - slowing or

reduction of the flow of current reduction of the flow of current – Resistance depends on the Resistance depends on the

material, length of material, and material, length of material, and the cross sectional area of the the cross sectional area of the material through which the current material through which the current is moving.is moving.

A

LR R is resistance, is resistivity,

L is length, A is the cross sectional area

Ohm’s LawOhm’s Law

Ohm’s Law stated – The ratio of Ohm’s Law stated – The ratio of V/I is a constant, where V is the V/I is a constant, where V is the voltage applied across a piece of voltage applied across a piece of material (such as wire) and I is material (such as wire) and I is the current through the the current through the material. R is the resistance of material. R is the resistance of the piece of material.the piece of material.

– Units: Ohms (Units: Ohms () = Volt/amp) = Volt/ampCurrent

VoltageResistance

I

VR

Electric Power Electric Power

When there is current (I) in a When there is current (I) in a circuit as a result of a voltage (V), circuit as a result of a voltage (V), the electric power (P) delivered to the electric power (P) delivered to the circuit is:the circuit is:–– Units: watts = amp x volt = J/sUnits: watts = amp x volt = J/s

voltagecurrentPower VIP

Electric PowerElectric Power

Many electrical devices become hot when Many electrical devices become hot when provided with sufficient electric power. provided with sufficient electric power. Toasters, irons, space heaters, heating Toasters, irons, space heaters, heating elements in electric stoves, and incandescent elements in electric stoves, and incandescent light bulbs. In such cases it is possible to light bulbs. In such cases it is possible to obtain two equivalent power equationsobtain two equivalent power equations

When electric energy is transferred into When electric energy is transferred into thermal energy in a resistor, the increase in thermal energy in a resistor, the increase in thermal energy is:thermal energy is:

– units: Kilowatt hour or Joules units: Kilowatt hour or Joules

RIP 2 R

VP

2

RtIQ 2

Current in electric Current in electric CircuitsCircuits An electric Circuit is An electric Circuit is

a closed loop. a closed loop. Basic Circuits consist Basic Circuits consist

of three things:of three things:– Electron pump Electron pump

(Battery)(Battery)– Device that reduces Device that reduces

potential. (User)potential. (User)– Conducting Conducting

connectionsconnections (Wires) (Wires)

Direct Current Circuits:Direct Current Circuits:

Circuit – closed loop in Circuit – closed loop in which current can flowwhich current can flow

Basic simple circuitBasic simple circuit– Voltage sourceVoltage source– Voltage usesVoltage uses– conducting connections conducting connections

(wire)(wire) Diagrams for electric Diagrams for electric

circuitscircuits– Describe in wordsDescribe in words– use use

photographs/drawingsphotographs/drawings– Use symbols Use symbols

(schematics)(schematics)

Schematic SymbolsSchematic Symbols

Drawing Schematic Drawing Schematic CircuitsCircuits Draw symbol for battery and indicate “+” Draw symbol for battery and indicate “+”

and “-“ terminalsand “-“ terminals Draw wire from “+” to the voltage user and Draw wire from “+” to the voltage user and

draw its symbol.draw its symbol. If a point where there are two current paths, If a point where there are two current paths,

draw connection symbol and follow one path draw connection symbol and follow one path to the user. Return to the second path and to the user. Return to the second path and draw to its user and continue until paths join.draw to its user and continue until paths join.

Follow path to the “-“ terminal Follow path to the “-“ terminal Check workCheck work Connect ammeter in seriesConnect ammeter in series Connect voltmeter in parallelConnect voltmeter in parallel

ObjectivesObjectives

Describe the configuration of a Describe the configuration of a working circuitworking circuit

Interpret circuit diagramsInterpret circuit diagrams Describe the characteristics of series Describe the characteristics of series

connectionsconnections Determine equivalent resistance of Determine equivalent resistance of

circuits having two or more resistors.circuits having two or more resistors. Explain the cause of short circuitsExplain the cause of short circuits Homework:Homework:

– Read Pages 531-541Read Pages 531-541– Pg 534 #1-3, Pg 537 # 6-9Pg 534 #1-3, Pg 537 # 6-9

Series CircuitsSeries Circuits Only one path for current to followOnly one path for current to follow User followed by another user (ie. User followed by another user (ie.

Resistor followed by a light)Resistor followed by a light)

...321 VVVVequ

…

Series Circuit RulesSeries Circuit Rules

Current is the same for each user

The effective resistance is the sum of all resistors in the series

– The sum of the voltage drop is

equal to the total voltage drop –

...321 RRRRequ

...321 VVVVequ

Parallel CircuitsParallel Circuits

Two or more paths for Two or more paths for current to followcurrent to follow

Parallel Circuit RulesParallel Circuit Rules

Total current in the circuit is the sum Total current in the circuit is the sum of the current in all its paths of the current in all its paths (branches)(branches)

– The equivalent resistance decreases The equivalent resistance decreases

with more parallel resistorswith more parallel resistors–

Voltage is the same in each path.Voltage is the same in each path.

...321 IIIItot

...1111

321

RRRRequ

+ -

ObjectivesObjectives

Describe the configuration of a working circuitDescribe the configuration of a working circuit Distinguish between series and parallel circuitsDistinguish between series and parallel circuits Describe the characteristics of series Describe the characteristics of series

connections and of parallel connections.connections and of parallel connections. Interpret circuit diagramsInterpret circuit diagrams Determine equivalent resistance of circuits Determine equivalent resistance of circuits

having two or more resistors.having two or more resistors. Explain the cause and prevention of Explain the cause and prevention of

overloading household circuits.overloading household circuits. Homework:Homework:

– Read Pages 531-541Read Pages 531-541– Pg 534 #1-3, Pg 537 # 6-9Pg 534 #1-3, Pg 537 # 6-9