Science 9

Science 9Aim: ACDCAgendaScience Sizzler (Ashton, Connor)ACDC notesQuizHand out study guides for unit testNext class Finish notesDIRECT 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 51 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

32Capture 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!!