Energy and Cost

Energy  Energy: the ability to do work all appliances need energy to work ex.a hair dryer needs to be plugged in to get energy to work ex.a remote control needs energy from batteries to work ex.a light bulb needs electrical energy to shine bright ex.solar panels use energy from the sun to heat a house What is energy?

Power  Power: the rate at which energy is produced is the product of potential difference (voltage) & current intensity What is power?

Symbols and Units Symbol = Units = Symbol = Units =

E = P t Energy Joules (J) Power Watts (W) Time Seconds (s)

A stereo has a power rating of 200W & is used for 1800 seconds. How much energy is used? E = Pt E = (200)(1800) E = 360,000 J 360,000 Joules of energy were used to work the stereo

A video game has a power rating of 175W & is used for 3600 seconds. How much energy is used? E = Pt E = (175)(3600) E = 630,000 J 630,000 Joules of energy were used to work the video game

A hair dryer has a power rating of 425W & is used for 10 minutes. How much energy is used? E = Pt E = (425)(600) E = 255,000 J 255,000 Joules of energy were used to work the hair dryer Time must be in seconds 10 min x 60 = 600 seconds

P = V I Power Watts (W) Potential Difference Volts (V) Current Amps (A)

A toaster requires 120V & 6A to work. What is its power? P = VI P = (120)(6) P = 720 W The toaster has 720 watts of power

An appliance requires 240V & 2A to work. What is its power? P = VI P = (240)(2) P = 480 W The appliance has a power of 480 watts

An appliance requires 120V & 12A to work. It is used for 900 seconds. How much energy is used? P = VI P = (120)(12) P = 1440 W Tricky Question E = Pt E =(1440)(900) E =1,296,000 J

An appliance uses 225V & 4A to work. It is used for 60 minutes. How much energy is used? P = VI P = (225)(4) P = 900 W Tricky Question E = Pt E =(900)(3600) E =3,240,000 J 60min x 60

Activties  Worksheet #15

Cost Every time you use an appliance it costs money……how do you calculate how much it will cost? (Usually Given)Must be in kW Must be in hours Remember: 1000 watts = 1 kW

A 4800 watt television is used for 5 hours. If the cost of electricity is $0.04kWh, what would your bill read? (How much would it cost?) Cost = cost of electricity x Power x Time 4800 W = 4.8 kW

A 1500 watt hair dryer is used for 30 minutes. Electricity costs $0.05/kWh. How much does it cost to use this hair dryer for the period indicated? Cost = cost of electricity x Power x Time 30 min ÷ 60 min = 0.5 hrs 1500 W = 1.5 kW

A 3.9 kilowatts curling iron is used for 10 minutes once a day. Electricity costs $0.05/kWh. How much does it cost to use this curling iron for a week? Cost = cost of electricity x Power x Time 10 min ÷ 60 min = hrs X 7 days

Cost & Rating Plates  Every electrical appliance has a rating plate.  Rating plates allow us to calculate the electrical cost of an appliance. Model:VCANN-1977 Serial No: V60 Hz4000 W POWER Look for power

The rating plate for an electric hair dryer is given below. Model:LHOPE W200V40Hz If the dryer is used for 30 minutes a day & the cost of electricity is $0.04/kWh, how much would it cost to use every day? Cost = cost of electricity x power x time Cost =($0.04/kWh) x (1.5kW) x (0.5h) Cost =$0.03 or 3¢

The rating plate for a television is given below. Model:CANNHOPE W250V60Hz If the TV is used for 2 hours a day & the cost of electricity is $0.05/kWh, how much would it cost to use for a 30-day month? Cost = cost of electricity x power x time Cost =($0.05/kWh) x (2.5kW) x (2h) Cost =$0.25 x 30 days Cost =$7.50

If the appliance is used for 1 hour a day & the cost of electricity is $0.0475/kWh, how much would it cost to use every day? The rating plate for an electric appliance is given below. Model:NOV-05 30Hz 200V6A Cost = cost of electricity x power x time Cost =($0.0475/kWh) x (1.2kW) x (1h) Cost =$0.057 or $0.06 No power!! Recall P = VI P = (200)(6)P = 1200 W ?

If the appliance is used for 3 hours a day & the cost of electricity is $0.05/kWh, how much would it cost to use for a week? The rating plate for an electric appliance is given below. Model:RAF V 0.2A Cost = cost of electricity x power x time Cost =($0.05/kWh) x (0.075kW) x (3h) Cost =$ No power!! Recall P = VI P = (375)(0.2)P = 75 W ? x 7 days Cost =$0.08

The rating plates of four different electric appliances are given below GIN-4445 MAC-2453 I8JUL-6712 MANDANE W 120V 60 HZ 2 A 250 V 66 HZ 10 A 125 V 1400 W 15 A 140 V Each appliance is used for 4 hours. Which of these appliances would be the most expensive to use? A) D) C) B) Since the cost and time are the same you must just look for power… P = V x I P = 10 x 125 P = 1250 W P = V x I P = 2 x 250 P = 500 W By comparing Power it is clear to see that appliance “C” would be the most expensive!

 Joule : a unit of energy Ex.: 25 g of candy contains J  ampere : a quantity of charges per time Ex.: 15 ampere breaker  Watt : a unit of power Ex.: 100 W light bulb  Volt : energy per unit charge Ex.: AA battery has 1.5 volts Recalling Units J A W V

Important Units to Remember JoulesWatts WskW kwh VAs It is important to remember the following units for energy and power.

Electricity uses the following units: 1. Watt4. Kilowatt-hour 2. Volt5. Joule 3. Ampere Which of the above are units of energy? A) 1 and 3B) 2 and 4 C) 1 and 5D) 4 and 5 EnergyPower JoulesWatts WskW kwh VAs

Which of the following units are not units of energy? 1. W 2. VAs 3. J 4. A 5. kWh 6. Ws A)1, 3, and 4 B) 1 and 4 C)1, 4, and 6 D) 4 and 5 EnergyPower JoulesWatts WskW kwh VAs

KEY POINTS - FORMULAS E = P x t P = V x I Cost = cost of electricity x P x t **make sure you have the correct units in these formulas** - UNITS EnergyPower JoulesWatts WskW kwh VAs