Science 9

Science 9Aim: Electrophoresis and Building a circuitAgendaScience Sizzler (Ashton, Connor)Electrophoresis and Building a circuit notesNext classElectrochemistryThe Study of Chemical Reactions involving Electricity

Electrochemistry ApplicationsElectrolysisProcess using electricity to split molecules into their elements.Ex. split water into hydrogen and oxygen gas using electricity

Uses include: making PVC pipe producing fuel for space shuttleElectrochemistry ApplicationsElectroplating-coating other materials with metals

Example: - Electroplating jewelry with gold or silver

GOLD PLATED MACBOOKCircuits (what we already know) A) An Energy Source = Supplies electronsB) A Conductor = Material allowing flow of electronsC) A Load = A device that converts electrical energy to another form of energy (ex. heat or light)D) A Switch (Optional) = Closes and opens a circuit

ABCDMicroscopically ExaminingWithin the substances atom, electrons are tightly bound to the positively charged nucleus therefore resist moving between the atoms (i.e. No Potential for Electrical Current)INSULATORS

Microscopically ExaminingWithin the substances atom, electrons are NOT tightly bound to the positively charged nucleus therefore they are freer to move between atoms & do so when connected to an electrical sourceCONDUCTORS

Most CONDUCTORS are not perfectMeaning that the atoms electrons move quite freely when an electrical current is applied, but

there is some ELECTRICAL RESISTANCE(electrons opposition to flow) SuperconductorsPerfect Conductors Materials that have no resistance to electron flow

Examples: - Mercury when temperature lowered - Other substances lowered to close to absolute zero (-273oC)

RESISTORS A type of conductor useful in electrical devices Allows electric current to pass, but provides a good amount of resistance Measured in Ohms ()RESISTORS Substance with More Resistance = More Energy Per Passing Electron

The resistor radiates the gained energy to its surrounding as heat or light

Think light bulb

12THE SWITCHMechanism used to turn electricity on and off in a circuit

ON = two conductors pressed together, allowing current to flow between the twoOFF = two conductors are separated, preventing current to flowUsually enclosed in an insulator to prevent shocks and short circuits

ON OR OFF OR IN BETWEENInstead of turning it on or off, sometimes we want to gradually change the current flow in a circuit

to do this we use a Rheostat (or Variable Resistor)

Rheostat (or Variable Resistor) Increase or Decrease the amount of current in a circuit

THE WATER ANALOGYUsing the movement of water as an analogy can help us better understand electricity

The Water Analogy Source Like flowing water, electricity comes from a source

In both, the source must be constantly replenished for the current to continue

Example: Snow Pack in the Mountains

Example:Electrical GeneratorThe Water Analogy CurrentMore Water = More Powerful River Current

More Electrons = More Powerful Current in the Conductor

The Water Analogy - VoltageWhen water is pumped up hill, it gains gravitational potential energy and will flow back down

Electrical cells, batteries, & generators pump electronsto point with higher electrical potential (voltage)

The Water Analogy - ResistanceLike water smashing into rocks, electricity encounters resistance

Current decreases as you add resistance, therefore shorter & thicker conducting wires have the least amount of resistance

Controlling the Current Flow!Quietly Read Page 297 302 Questions # 1 - 7German Scientist Georg Simon Ohm proved a mathematical link between VOLTAGE, CURRENT, & RESISTANCE

OHMS LAW STATESAs long as temperature stays the same The resistance of a conductor stays constant The current is directly proportional to voltage being applies (increase voltage = increase current) If voltage stays the same, but if a stronger resistor is used, current decreases OHMS LAWV = Voltage (volts) I = Current (amps)R = Resistance (ohms)VIROHMS LAWCalculating: V = Voltage (volts)VIRxOHMS LAWCalculating I = Current (amps)VIROHMS LAWCalculating R = Resistance (ohms)VIREXAMPLE QUESTIONS:A 30 V battery creates a current through a 15 resistor. How much current is created?

2) A motor has and internal resistance of 40 . The motor is in a circuit with a current of 4.0 A. What is the voltage?

3) A current of 625 mA runs through a bulb that is connected to 120 V. What is the resistance of the bulb? (HINT: Units need to be in A, V, & )BUILDING ELECTRICAL CIRCUITS The most economical way to build a circuit is in a simple loop

But we dont want the entire circuit to fail if one component breaks down!

All Circuits Have A) An Energy Source= Supplies electrons B) A Conductor = Material allowing flow of electrons C) A Load= A device that converts electrical energy to another form of energy (ex. heat or light) D) A Switch (Optional) = Closes and opens a circuit

Electrical SourceSwitchLoad (ex. Bulb)ConductorDRAWING CIRCUITSSchematic Diagrams = are used by engineers, designers, and scientists to map out electrical circuits.

They include special universal symbols that show the components and connections clearly

THE BASIC ELECTRICAL SYMBOLSSYMBOLREPRESENTSDESCRIPTIONConductorCellBatteryLamp (bulb)ResistorSwitchAmmeterVoltmeterRheostatMotorFusePage 312

SERIES vs. PARALLEL CIRCUITSEver noticethat when one bulb on a string of lights burns out, the whole string of lights doesnt work??

You must search for the bad bulb!!

Why??Because the current must travel through each load (bulb) in the circuit

So when one bulb breaks, the current flow stops breaking the entire circuit!Example of a Series Circuit

SERIES CIRCUITSthere is only 1 path for the current to flow throughif the pathway is interrupted (broken) the circuit doesnt work

SERIES CIRCUITSadding components increases the total resistance, which decreases the current (ie adding one more light bulb makes them all dimmer)

SERIES CIRCUITSin your house, switches are wired in series with other components (wall plugs, lights) which makes it possible to turn off all the electricity in that circuit

PARALLEL CIRCUITSprovides more than 1 path for the current to flow through

PARALLEL CIRCUITSa break or interruption in one pathway does not affect the rest of the pathways in the circuit

PARALLEL CIRCUITSadding new components (with new pathways) does not affect the resistance in any of the other pathways

Using Parallel Circuits in HOUSEHOLD WIRINGWe want to be able to control each individual component (load) separately A switch on each branch controls only controls the device in that branch1 switch in series is an important safety precaution in case we need to turn off electricity to all them MICROCIRCUITS (aka microchips)Microscopic circuits are made up of transistors and resistors

Can contain more than 1 million components per centimeter!!!

MICROCIRCUITSSwitches are not practical for these tiny circuits.

So instead, we use Transistors A small solid material (usually silicon) consisting of 3 layers. Middle layer controls the current

Making Schematic Diagrams!!Draw and label (using the appropriate symbols) 1) A series circuit that includes: a battery, a switch, 2 lamps, a voltmeter, a fuse, and a conductor2) A parallel circuit that includes a battery, a conductor and 3 components: - one with a switch and a lamp- one with a lamp and a rheostat- one with resistor and a ammeterRemember: Parallel circuits should have a switch in series!!! DIRECT vs. ALTERNATING CURRENT

DIRECT vs. ALTERNATING CURRENTElectricity flows only in one direction Used by many common devices, such as iPods, computers, cell phones, calculators

DIRECT CURRENT (DC):Electricity flows back and forth (60 times per second)The power supplied to our homes is AC

ALTERNATING CURRENT (AC):Power companies generate Alternating Current and transmit it with High Voltage

Some lines carry a current with 500,000 volts!!

But this voltage must be reduced before the current can be used in our homes

TRANSFORMERSDevices used to change the amount of voltage with very little energy loss.

Can be Step-Down or Step-Up Transformers

STEP-DOWN TRANSFORMERSReduces Voltage

STEP-DOWN TRANSFORMERSPrimary Coil = AC current carrying wire is wrapped around one side of iron ring (called a core)Secondary Coil = Wire wrapped around other side

STEP-DOWN TRANSFORMERSThe AC flowing through the primary coil creates an alternating magnetic field, inducing a current in the secondary coil

if number of loops in the primary coil are greater than the number of loops in the secondary coil, voltage is lowered

10 Loops50 LoopsSTEP-UP TRANSFORMERSIncreases Voltage

STEP-UP TRANSFORMERSThe AC flowing through the primary coil creates an alternating magnetic field, inducing a current in the secondary coil

if number of loops in the primary coil are less than the number of loops in the secondary coil, voltage is increased

20 Loops5 LoopsGENERATING DC & ACDC Generators generate Direct CurrentGENERATING DC & ACDC Generators are very similar to DC Motors

Mechanical Energy Spinning the Armature (INPUT)

Spinning wires in the magnetic field creates an electrical current (OUTPUT)in the wires

GENERATING DC & ACAC Generators generate Alternating Current and are slightly different from DC Generators

Both ends of the wire (A & B) are connected to individual slip rings.

As the wire rotates around in the magnetic field, one end (A) goes up its slip ring while the other (B) goes down

Wire A then starts going down and wire B goes up (this change indirection creates AC)

ABPOWERThe rate at which a device converts energyMore Power = Faster Energy ConversionUnits = watts (W)CALCULATING POWERFORMULA:

Power (P) = Current (I) X Voltage (V) Units (W = watts) (A = amps) (V = volts)

Example Question: A hair dryer has 1000 W of power and is plugged into a 120 V outlet. What is the current flowing through it?CALCULATING ENERGYFORMULA:

Energy (E) = Power (P) X Time (t)Units (J = joules) (W = watts) (s = seconds)

CALCULATING ENERGYFORMULA:

Energy (E) = Power (P) X Time (t)Units (kWh = kilowatt hours) (kW = kilo watts) (h = hours)

USING KILOWATT HOURS (instead of Joules)Example QuestionsA microwave oven has 800 W of power. If you cook a roast in this oven for 30 minutes, how much energy is being used to convert the electrical energy to hear?A microwave oven has 0.8 kW of power. If you cook a small turkey in this oven for 2 hours, how much energy is being used to convert the electrical energy to hear?

GIZMO LAB Go to LAB 63 For next class!!!PRACTICE Pg 338 # 6-9

Electrical Circuits GIZMO LAB!

1)Go to www.learnalberta.ca2) Under Find Resources, searchScience Grade 9 Keyword = Circuits 3) Use the worksheet as a guide GIZMO LAB - InstructionsPower and Energy Calculation ExamplesA toaster oven uses 1050 W and bakes a small pie in 30 minutes. How many Joules of electricity did it use? How many kilowatts?

In every energy transformationsome energy is wasted(meaning it cannot be used)Total InputEnergyUseful OutputEnergyWASTE% EFFICIENCYFunctioning in the best possible manner with the least possible waste

In energy conversions The ratio of the useful energy output to the total energy input in a device or system

% Efficiency = Useful Output Energy (in joules) X 100 Total Input Energy (in joules)% Efficiency Calculation ExamplesAn incandescent bulb produces 6 J of useful light after receiving a total of 120 J of electrical energy. What is the % efficiency?

If a fluorescent light bulb is determined to be 25% efficient and has a useful output of 8 J, how much energy in total was supplied?

Limits to EfficiencyNo device or energy conversion can ever be 100% efficient!!

Any movement results in at least some thermal energy that is not useful. Also, wasteful sound energy is common in many energy transformation BUT WE CAN MAKE THINGS MORE EFFICIENT!Minimizing the amount of heat released during energy conversions (ex. adding insulation to different devices)Review of AC GeneratorsGenerators require an input of mechanical energy to spin turbines (the armature) and rotate the wires in the magnetic field

AB(this creates an electrical current in the wire)Generating ElectricityApprox. 65% of all the worlds electric power is generated by the burning of fossil fuels (oil, coal, and natural gas)

Why are they called Fossil Fuels? Formed from decomposed remains of plants and animals Using Heat

= burning of coal heats water and produces steam = steam pressurized and moves to generator = steam provides mechanical energy to run generator

123123Generating Electricity Using HeatEarths core is very hot.

This heat in Earths crust creates steam.

The steam is channeled through pipes and provide the mechanical energy needed by the generator. Generating Electricity Using Geothermal Energy

75Capture the energy of falling water.. through dams.

The pressurized flow of water provides the mechanical energy needed by the generator Generating Hydro-Electricity

Other Energy SourcesTides = the tides moving water provides the mechanical energy

Wind = turns the turbines (mechanical energy)

Sunlight = silicon-based solar cells absorb solar energy

Batteries = more than one electrochemical cell Electricitys Impact on the Environment and SocietyImportant Reading: Page 351 358Questions for Practice: Page 353 # 1 5 / 358 # 1 - 5 TAKE HOME QUIZ DUE MONDAY!!