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Science 9

Science 9. Aim: ACDC. Agenda. Science Sizzler ( A shton, Connor) ACDC notes Quiz Hand out study guides for unit test Next class – Finish notes. DIRECT vs. ALTERNATING CURRENT. DIRECT vs. ALTERNATING CURRENT. DIRECT CURRENT ( D C):. Electricity flows only in one direction

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Science 9

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  1. Science 9 Aim: ACDC

  2. Agenda • Science Sizzler (Ashton, Connor) • ACDC notes • Quiz • Hand out study guides for unit test • Next class – Finish notes

  3. DIRECT vs. ALTERNATING CURRENT

  4. DIRECT vs. ALTERNATING CURRENT DIRECT CURRENT (DC): • Electricity flows only in one direction • Used by many common devices, such as iPods, computers, cell phones, calculators ALTERNATING CURRENT (AC): • Electricity flows back and forth (60 times per second) • The power supplied to our homes is AC

  5. 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

  6. TRANSFORMERS Devices used to change the amount of voltage with very little energy loss. Can be “Step-Down” or “Step-Up” Transformers

  7. STEP-DOWN TRANSFORMERS • Reduces Voltage

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

  9. STEP-DOWN TRANSFORMERS The 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 50 Loops 10 Loops

  10. STEP-UP TRANSFORMERS • Increases Voltage

  11. STEP-UP TRANSFORMERS The 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 5 Loops 20 Loops

  12. GENERATING DC& AC DC Generators generate Direct Current

  13. GENERATING DC& AC DC 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

  14. GENERATINGDC & AC AC 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) B A

  15. POWER • The rate at which a device converts energy • More Power = Faster Energy Conversion • Units = watts (W)

  16. CALCULATING POWER FORMULA: 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?

  17. CALCULATING ENERGY FORMULA: Energy (E)= Power (P) X Time (t) Units (J = joules) (W = watts) (s = seconds)

  18. CALCULATING ENERGY USING KILOWATT HOURS (instead of Joules) FORMULA: Energy (E)= Power (P) X Time (t) Units(kW●h = kilowatt hours) (kW = kilo watts) (h = hours)

  19. Example Questions • A 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?

  20. PRACTICE  Pg 338 # 6-9 GIZMO LAB  Go to LAB 51 For next class!!!

  21. Electrical Circuits • GIZMO LAB!

  22. GIZMO LAB - Instructions 1)Go to www.learnalberta.ca2) Under “Find Resources”, searchScience  Grade 9  Keyword = “Circuits”3) Use the worksheet as a guide

  23. Power and Energy Calculation Examples • A toaster oven uses 1050 W and bakes a small pie in 30 minutes. How many Joules of electricity did it use? How many kilowatts?

  24. In every energy transformation… WASTE …some energy is wasted (meaning it cannot be used) Useful OutputEnergy Total InputEnergy

  25. % EFFICIENCY Functioning in the bestpossiblemannerwith 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)

  26. % Efficiency Calculation Examples • An 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?

  27. Limits to Efficiency No 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

  28. … BUT WE CAN MAKE THINGS MORE EFFICIENT! Minimizing the amount of heat released during energy conversions (ex. adding insulation to different devices)

  29. Review of AC Generators Generators require an input of mechanical energy to spin turbines (the armature) and rotate the wires in the magnetic field B A (this creates an electrical current in the wire)

  30. Generating Electricity Approx. 65% of all the world’s 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

  31. Generating Electricity Using Heat Using Heat… = burning of coal heats water and produces steam = steam pressurized and moves to generator = steam provides mechanical energy to run generator 2 1 3 1 2 3

  32. Generating Electricity Using Geothermal Energy Earth’s core is very hot. This heat in Earth’s crust creates steam. The steam is channeled through pipes and provide the mechanical energy needed by the generator.

  33. Generating Hydro-Electricity Capture the energy of falling water.. through dams. The pressurized flow of water provides the mechanical energy needed by the generator

  34. Other Energy Sources Tides = the tide’s 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

  35. Electricity’s Impact on the Environment and Society Important Reading:  Page 351 – 358 Questions for Practice: Page 353 # 1 – 5 / 358 # 1 - 5 TAKE HOME QUIZ  DUE MONDAY!!

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