Topic 3.0 Converting electricity and efficiency

1. Topic 3.0 Converting electricity and efficiency

2. I. Forms and Transformations • Energy – the ability to do work A. Forms of Energy • Chemical energy – potential energy that is released when chemicals react Ex. Food, batteries 2) Electrical energy – energy of electron flow (transfer) Ex. electrical circuits

4. I. Forms and Transformations A. Forms of Energy 3) Mechanical energy – energy of an object because of its motion, or potential to move. Ex. An elastic has the potential to move when pulled back; when moving has motion 4) Thermal energy – the kinetic energy of a particle in an object; the faster it moves the more kinetic energy is present (the hotter the temperature)

6. I. Forms and Transformations B. Transformations Predict the input (starting) and output (ending) energy for each converting device: • Toaster • Batteries • Flashlight • Blender

7. I. Forms and Transformations B. Transformations e) Radio f) TV g) Human body h) Explosives

8. I. Forms and Transformations • Thermocouple – a device that converts thermal energy to electrical energy • Made of two different metals that heat (conduct) at different rates • Produces electricity

9. DEMO: Transforming Heat into Electricity • Pg. 322 • Record any changes in the voltmeter when a thermocouple is changed from ice water to boiled water

10. II. Electrical and Mechanical Energy Transformations A. Famous Discoveries: • Oersted : A wire with current produces a magnetic field (deflects a compass) -Oersted video • Michael Faraday: Moving a magnet through coiled wire causes an electrical current (electromagnetic induction) *These discoveries led to the motor! Faraday simulation

11. II. Electrical and Mechanical Energy Transformations B. How a Motor Works • Electromagnet– a magnet made by wrapping wire (with current) around an iron core

12. B. How a Motor Works • Parts to a motor: • Commutator – a split ring breaks the flow of electricity for a moment and reverses the current • Brushes – contact the commutator and are connected to a battery

13. B. How a Motor Works • Parts to a motor: 3) Armature – a rotating shaft to which the wire is attached (electromagnet) >this continues to spin due to momentum Motor #2 Video

14. Connect to battery brushes commutator Armature (contains wire) magnets

15. Parts of a Motor

16. II. Electrical and Mechanical Energy Transformations B. How a Motor Works • Electromagnet (with running current) is placed between the poles of a permanent magnet. 2. The brushes bring current from the power sources to the commutator – is then transferred to armature. 3. Electromagnet (armature) turns to align N of armature to S of magnet (opposite attract)

18. 4. Just as the armature aligns with the magnet, the commutator reverses the current in the electromagnet • Causes the poles of the electromagnet (armature) to reverse • 5. The armature gets attracted to opposite pole and continues to spin (creates mechanical energy)

20. II. Electrical and Mechanical Energy Transformations C. Types of Current • Direct current (DC) – electricity flows only in one direction Ex. Current from batteries – iPod, cell (Edison)

21. II. Electrical and Mechanical Energy Transformations C. Types of Current 2) Alternating current (AC) – electricity that flips direction 60 times per second Ex. Currents from outlets (Tesla) AC vs DC Video

22. II. Electrical and Mechanical Energy Transformations D. Transporting Current • Power companies transport electrical current as: • High voltage (50 000V) • AC current to reduce energy loss • However, the voltage must be reduced to use in homes (120V) – done with a transformer

23. II. Electrical and Mechanical Energy Transformations D. Transformation of Voltage Transformers – used to increase or decrease voltage; • The current is fed into the primary coil which “induces” (causes) a current in the secondary coil

24. D. Transformation of Voltage • Step-up – increases voltage - primary coil has less coils than secondary coil b) Step-down – decreases voltage -primary coil has more coils than secondary coil

26. Ex. Would a power company use a step up or step down generator to increase the voltage for transportation of current? b) Would the secondary coil have less or more coils than the primary?

27. II. Electrical and Mechanical Energy Transformations E. Generating Electricity • Motors use current electricity (created by magnetism) to create mechanical energy. (Oersted’s idea) • Generators take mechanical energy and create electrical energy by using electromagnetic induction (Faraday’s idea)

29. E. Generating Electricity • To increase the amount of energy produced you can: • 1. Increase the speed of rotation. • 2. Increase the strength of the magnet • 3. Increase the number of coils

30. III. Energy Input/Output A. Measurements • 1. Power – the rate at which a device converts energy • Measured in watts (W or J/s) • The larger the conversion, the larger the power rating

31. III. Energy Input/Output Ex. If a lightbulb is 60W it converts how many Joules of energy per second? What is the energy conversion?

32. III. Energy Input/Output The formula for power is: P = I V P – power (W) I- current (A) V – voltage (V)

33. Ex. What current does a 60W bulb require using 120V?

34. Ex. How much power does a lamp with two 60W bulbs require using a 120V socket?

35. III. Energy Input/Output A. Measurements 2. Energy E = Pt E –energy [J] P – power [W] t – time [s]

36. A. Measurements 2. Energy • Converting hours to seconds: x 3600 • Converting mins to seconds : x 60

37. III. Energy Input/Output • Ex. How much energy is consumed by a laptop that uses 90W of power and is left on for 8 hours?

38. III. Energy Input/Output • Kilowatt hours is another unit for Energy • E = P x t • = kW x h • = kWh

39. III. Energy Input/Output • How much energy does a 1000W oven use in 3 hours of baking? b) If it cost $0.0225/ kWh for energy, how much did it cost to run the oven?

40. III. Energy Input/Output B. Law Conservation of Energy • Appliances usually have listed an “efficiency” rating . This communicates how much energy needed is actually used “usefully”. Ex. A tungsten lightbulb is only 5% efficient. Where does the other 95% of energy not used “usefully” go?

41. III. Energy Input/Output B. Law Conservation of Energy This law states that: “Energy cannot be created nor destroyed, only converted to other forms (waste)” What energy forms are “useful” for a lightbulb? What form of energy is the rest converted to?

42. III. Energy Input/Output B. Law Conservation of Energy KEY IDEA: Energy not used usefully is MAINLY converted to thermal energy!

43. III. Energy Input/Output B. Law Conservation of Energy Ex. For each of the following devices, list the “useful” and “waste” energy: • Motor – useful: - waste: • Muscles – useful: - waste: c) TV – useful: -waste:

44. III. Energy Input/Output C. Efficiency • Is how much of the “input” energy is converted to “useful output” %Efficiency = useful output x 100% input

45. Ex. Calculate how efficient a toaster is if it uses 1350J and only 1000J is converted to heat.

46. Skill Practice pg. 336

47. III. Energy Input/Output D. Limits to Efficiency • Rarely are devices 100% efficient • Anytime parts are moving, friction results in a conversion of useful energy to heat energy (waste)

48. III. Energy Input/Output D. Limits to Efficiency • How can we increase efficiency of appliances? Apply lubricants (oil) to reduce friction Apply insulation (reduce heat loss)