WELCOME TO PERIOD 12. Homework Exercise #11 is due today.

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1 WELCOME TO PERIOD 12 Homework Exercise #11 is due today.

2 PHYSICS 1103 PERIOD 12 What is power? How is electrical energy measured? How can you save money when using electricity? Remember to put away your phone. No calls or texting during class.

3 Power Power is a rate describing the amount of work done or energy transferred per unit of time: Power = Work OR Power = Energy time time Power is measured in units of watts. 1 watt = 1 joule/second In English units, power is measured in footpounds/second (ft-lbs/sec) or horsepower (hsp).

4 Power requirements Light the bulbs using power generated by your muscles. Compare the appliance wattages (given on the appliances) to the measured wattage. How does increasing the load on the drill affect its power requirement?

5 Measuring power with a wattmeter 1) Plug the wattmeter into the power strip. 2) Plug the appliance into the outlet in the front of the wattmeter. 3) Turn the appliance on. The appliance wattage appears in the display screen. Select Mode Plug in appliance

6 Human power How much power is generated when a person climbs the classroom stairs? Power = Epot = M g h time t What is the weight (M g) of the person? How high did the person rise (h)? How long did it take to climb the stairs (t)?

7 Energy to ride the bike How many watts of power light the bulbs connected to the exercise bicycle? How long were the bulbs lit? Find the energy to light the bulbs by solving the power equation for the energy, E. P = E t

8 Measuring electricity Electric companies charge for electricity in units of kilowatt hours (kwh). One kilowatt hour = 1,000 watts of power provided for one hour. The spinning disc on the kilowatt-hour meter measures the electricity provided. The disc is connected with gears to the hands on the kilowatt-hour meter dials that show the kwh used.

9 Calculating the cost of electricity On an electric bill, find: 1) The monthly cost of electricity and 2) The number of kilowatt hours of energy used. Use a ratio to find the cost per kilowatt hour (kwh): monthly cost of bill = cost monthly kwh used kwh

10 Using ratios to find electricity costs Find the total cost of electricity used: If electricity costs 15 cents/kwh, what is the cost of 244 kwh of electricity? 244 kwh x $0.15 = $36.60 kwh Find the kilowatt-hours used: If electricity costs 15 cents/kwh, how many kwh can you buy for $45.00? $45.00 x 1 kwh = 300 kwh $0.15

11 Example: the cost of using a light bulb 1) How many kilowatt hours of energy are used when a 100 watt light bulb burns for 1,200 hours? 1kilowatt 100watts x x 1,200 hours 1,000watts 2) If electricity costs $0.10/kWh, how much does this 120 kwh cost? $0.10 x 120 kwh = $12.00 kwh 120 kwh Find the cost of using the incandescent and compact fluorescent bulbs. Subtract to find the cost savings.

12 Payback time Payback time is the time it takes to recover the additional cost of purchasing an energy efficient, more expensive appliance from the savings in energy. An energy-efficient dishwasher costs $80 more than a less efficient dishwasher. The energy-efficient dishwasher saves $20 each year in operating costs. What is the payback time for the dishwasher? additional cost = $80 x 1 year = 4 years savings each year $20

13 Cost of purchasing and using appliances A washer costs $950 to purchase and $75/year to operate. What is the total cost of this washer after 5 years? Total cost = purchase price + (cost x # of years) year Total = $950 + ($75 x 5 yrs) = $950 + $375 = $1,325 yr Find the total cost of using two appliances for the given number of years. Subtract to find the savings.

14 A windmill generates electricity A backyard windmill generates an average of 628 watts. How many kilowatt-hours per year does it generate? 628 watts x 1 kilowatt x # of hours/year =? kwh/yr 1,000 watts How much would it cost to purchase 10 years of these kwh from an electric company at $0.12/kWh? $0.12 x? kwh x 10 yrs =?? kwh yr

15 Payback time for the windmill How much would it cost to purchase and operate this windmill for 10 years? Total cost = purchase price + (cost x # of years) year Which costs less after 10 years generating electricity with the windmill or buying electricity from the electric company? How much less?

16 Table 12.1 on textbook page 93 Appliance Average Wattage of Appliance Annual Kilowatt- Hours Annual Cost at $0.10 per Kilowatt-Hour FOOD PREPARATION Blender $1.50 Coffee Maker $10.00 Dish Washer $36.00 Freezer (frostless, 15 cu ft ) $ Frying Pan $20.00 Mixer $1.30 Oven, microwave $30.00 Oven, self cleaning $ Range $ Refrigerator (frostless, 12 cu ft) $ Toaster $4.00 Waste Disposal $3.00 LAUNDRY Clothes Dryer $ Iron (hand) $14.00 Washing Machine $10.00 Water Heater $ COMFORT Air Conditioner (room) $ Electric Blanket $15.00 Dehumidifier $40.00 Fan (rollaway) $14.00 Heater (portable) $18.00 Humidifier $16.00 Lamp, Incandescent $18.00 Lamp, Fluorescent $2.70 Waterbed Heater $72.00 HYGIENE Hair Dryer $1.40 Shaver 14 2 $0.20 Toothbrush 7 5 $0.50 INFO/ENTERTAINMENT Television $5.60 Audio equpment $4.00 Personal Computer $22.50

17 BEFORE THE NEXT CLASS Read textbook chapter 13 Complete Homework Exercise 12 Bring a blank Activity Sheet 13 to class. Watch video 3 Edison s Miracle of Light for discussion during period 15

THE ELECTRIC HOOKUP. 1. Determine the wattage of various household appliances. 2. Calculate the number of kilowatt-hours used by appliances.

THE ELECTRIC HOOKUP. 1. Determine the wattage of various household appliances. 2. Calculate the number of kilowatt-hours used by appliances. Objectives: The student will do the following: THE ELECTRIC HOOKUP 1. Determine the wattage of various household appliances. 2. Calculate the number of kilowatt-hours used by appliances. 3. Identify the