1. Chapter 6 Section 9 Comparing Energy Consumption: More for Your Money

2. HW: PTG 6.9 p 698 #1-9 Learning Objective – Calculate the energy efficiency of electrical devices and distinguish between heat transferred by conduction, convection, and radiation. Success Criteria – Measure and compare the energy consumed by appliances. – Compare the costs of operating a variety of electrical appliances in terms of power ratings, amount of time each appliance is used, and billing rate. – Distinguish among the three ways of heat transfer. Learning Objective – Calculate the energy efficiency of electrical devices and distinguish between heat transferred by conduction, convection, and radiation. Success Criteria – Measure and compare the energy consumed by appliances. – Compare the costs of operating a variety of electrical appliances in terms of power ratings, amount of time each appliance is used, and billing rate. – Distinguish among the three ways of heat transfer. Do Now: – WDYS/WDYT p 691 Agenda – Do Now – Investigation 6.9 – Summary Do Now: – WDYS/WDYT p 691 Agenda – Do Now – Investigation 6.9 – Summary

3. Investigation 6.9 #1 and #2 – teacher demo #3 and #4 – using a hot plate #5 Repeat with heating coil #1 and #2 – teacher demo #3 and #4 – using a hot plate #5 Repeat with heating coil Record measurements and observations in log Heat water to same temperature as above Record measurements and observations in log Heat water to same temperature as above

4. Investigation 6.9 #6 - Calculate #7 – in notebook #8 and #9 #6 - Calculate #7 – in notebook #8 and #9 Energy (J)=power (W)×time (s) E = Pt Calculate costs for energy use Cost = energy × price per unit of energy Energy (J)=power (W)×time (s) E = Pt Calculate costs for energy use Cost = energy × price per unit of energy

5. Summary Are energy efficient methods worth the added cost of the appliance? Think of some scenarios where you think it would be cheaper, and some scenarios where it would not be cheaper. How does this impact the decisions of large global corporations?

6. HW: PTG 6.9 p 698 #1-9 Learning Objective – Calculate the energy efficiency of electrical devices and distinguish between heat transferred by conduction, convection, and radiation. Success Criteria – Measure and compare the energy consumed by appliances. – Compare the costs of operating a variety of electrical appliances in terms of power ratings, amount of time each appliance is used, and billing rate. – Distinguish among the three ways of heat transfer. Learning Objective – Calculate the energy efficiency of electrical devices and distinguish between heat transferred by conduction, convection, and radiation. Success Criteria – Measure and compare the energy consumed by appliances. – Compare the costs of operating a variety of electrical appliances in terms of power ratings, amount of time each appliance is used, and billing rate. – Distinguish among the three ways of heat transfer. Do Now: – Which method of heating is best and why? Agenda – Do Now – Physics Talk – Essential Questions Do Now: – Which method of heating is best and why? Agenda – Do Now – Physics Talk – Essential Questions

7. Physics Talk 6.9 How do you calculate the electrical energy consumed by a device? Assuming it uses power at a constant rate, you multiply the power of the device in kilowatts by the number of hours used. E=P·t Assuming it uses power at a constant rate, you multiply the power of the device in kilowatts by the number of hours used. E=P·t

8. Physics Talk 6.9 What if the appliance does not use power at a constant rate? The device uses a kilowatt meter that takes into account the amount of power used and the amount of time

9. Physics Talk 6.9 What are examples of devices that use a meter? Your refrigerator turns on and off at different rates, so it uses a meter You entire house is hooked up to a meter. This is how the power company charges you for electricity. Your refrigerator turns on and off at different rates, so it uses a meter You entire house is hooked up to a meter. This is how the power company charges you for electricity.

10. Physics Talk 6.9 Do all power companies use these meters? No. Some companies use statistical data about the appliances you have in your home and just automatically charge you the average amount.

11. Physics Talk 6.9 How can you calculate the cost of running an electronic device? Cost = energy × price per unit of energy Energy is measured in kilowatt-hours (1000 W·h = 1 kW·h). Cost = energy × price per unit of energy Energy is measured in kilowatt-hours (1000 W·h = 1 kW·h).

12. Sample Problem An electric coffee maker uses an average of 22.5 kW h of energy each month. If the family is charged $0.12/kW h for electricity, what is the average monthly cost of operating the coffee maker? Given: – E = 22.5 kW·h – Rate = $0.12/kW·h Unknown: – Cost Tool: – Cost = energy × price per unit of energy Solution: – Cost = 22.5 kW·h × $0.12/kW·h – Cost = $2.70 Given: – E = 22.5 kW·h – Rate = $0.12/kW·h Unknown: – Cost Tool: – Cost = energy × price per unit of energy Solution: – Cost = 22.5 kW·h × $0.12/kW·h – Cost = $2.70

13. Physics Talk 6.9 What is heat transfer? What are the three ways heat is transferred? What is heat transfer? What are the three ways heat is transferred? The transmission of heat energy from a warmer substance to a cooler substance. Conduction Convection Radiation The transmission of heat energy from a warmer substance to a cooler substance. Conduction Convection Radiation

14. Physics Talk 6.9 What is conduction? The transfer of heat energy from particle to particle between substances through contact or within a substance. Always requires direct contact! Example: When the heating coil touched the water molecules to heat them. The transfer of heat energy from particle to particle between substances through contact or within a substance. Always requires direct contact! Example: When the heating coil touched the water molecules to heat them.

15. Physics Talk 6.9 What is convection? The transfer of heat energy through the movement of air or liquid currents. Example: When the warmer water molecules moved away from the heat and transferred their energy to colder water molecules. The transfer of heat energy through the movement of air or liquid currents. Example: When the warmer water molecules moved away from the heat and transferred their energy to colder water molecules.

16. Physics Talk 6.9 What is radiation? The transfer of heat energy by emission of electromagnetic radiation in all directions. Examples: – When the microwaves heat the water. – When an object is warmed by being in the sun The transfer of heat energy by emission of electromagnetic radiation in all directions. Examples: – When the microwaves heat the water. – When an object is warmed by being in the sun

17. Physics Talk 6.9 Conduction, convection, and radiation

18. Essential Questions p 696 WDYTN P 697 – What does it mean? – How do you know? – Why do you believe? – Why should you care? P 697 – What does it mean? – How do you know? – Why do you believe? – Why should you care?