Electricity Calculations Percent Efficiency Power Cost Electrical Energy

Electrical Energy: a measure of the ability to do work The five most common

Energy is measured in units called Joules Energy is also measured in units called

Electrical Efficiency: comparison of the energy output of a device with the energy supplied

Electrical Efficiency Not all of the energy put in can be converted into useful

Electrical Efficiency is a measure of how much the energy that goes into a

Electrical Efficiency Calculating efficiency of a Device: percent efficiency = energy out energy in

Electrical Efficiency Example: A light bulb uses 100 J of energy and produces 35

Electrical Efficiency Try this: A toaster oven uses 1200 J of energy to produce

Electrical Power The rate at which electrical energy is produced or used. That is,

Power – Watt meter provide a convenient way to measure power consumption.

Power Watts to kilowatts (divide by 1000) 500 joules/sec = 500 watts = 0.

Power = Used Energy (Joules) time (seconds) Calculate the power of a kettle that

Cost of Operating Electrical Devices: cost to operate = power x used (k. W)

Example: a laptop computer uses a 75 W adapter when it is plugged in.

Electrical Efficiency Example: a laptop computer uses a 75 W adapter when it is

Electrical Efficiency Try this: Calculate the cost of operating a 1500 W hair dryer

Try this: Calculate the cost of operating a 1500 W hair dryer to dry

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Electricity Calculations: Percent Efficiency Power Cost

Electrical Energy: a measure of the ability to do work The five most common types of energy are: • • • Electrical energy Heat Light Sound Mechanical

Energy is measured in units called Joules Energy is also measured in units called kilowatt-hour (k. W h) kilowatt-hour (k. W�h) -1 k. W�h is the use of one killowatt of energy for -3 600 000 times as much energy as 1 Joule one hour

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Electrical Efficiency: comparison of the energy output of a device with the energy supplied e. g. Clothes dryers -older clothes dryer uses 800 k. W h per year -new clothes dryer uses 300 k. W h per year -they both do the same job but the new dryer is more than twice as efficient

Electrical Efficiency Not all of the energy put in can be converted into useful energy. Sometimes energy is lost (usually into heat energy) while the device is running. A lightbulb converts electrical energy to light energy. However bulbs get hot after they have been on for a period of time. The useful energy is light and the heat is wasted energy.

Electrical Efficiency is a measure of how much the energy that goes into a device is converted into useful energy. Calculating efficiency of a Device: percent efficiency = useful energy out total energy in No device is 100% efficient x 100%

Electrical Efficiency Calculating efficiency of a Device: percent efficiency = energy out energy in short form: % efficiency = Eout _____ Ein x 100%

Electrical Efficiency Example: A light bulb uses 100 J of energy and produces 35 J of light energy. Calculate the energy efficiency of the light bulb.

Electrical Efficiency Example: A light bulb uses 100 J of energy and produces 35 J of light energy. Calculate the energy efficiency of the light bulb. Given: Eout = 35 J Ein = 100 J Unknown: % efficiency

Electrical Efficiency Example: A light bulb uses 100 J of energy and produces 35 J of light energy. Calculate the energy efficiency of the light bulb. Select: % efficiency = Eout _____ x 100% Ein Solve: % efficiency = 35 J_ x 100% 100 J =35%

Electrical Efficiency Try this: A toaster oven uses 1200 J of energy to produce 850 J of thermal energy. Calculate the efficiency of the toaster oven.

Electrical Efficiency Try this: A toaster oven uses 1200 J of energy to produce 850 J of thermal energy. Calculate the efficiency of the toaster oven. Solve: % efficiency = 850 J x 100% 1200 J = 71% therefore the toaster oven is 71% efficient Now you try some calculations on your sheet

Electrical Power The rate at which electrical energy is produced or used. That is, the amount of energy transferred per second (Joules per second) Units: measured in Watts (W) or kilowatts (k. W) -one Watt is equal to one Joule of energy used per second e. g. 100 W light bulb uses four times as much energy per second as a 25 W bulb.

Power – Watt meter provide a convenient way to measure power consumption.

Power Watts to kilowatts (divide by 1000) 500 joules/sec = 500 watts = 0. 5 kilowatts 1500 joules/sec = 1500 W = 1. 5 k. W Try the conversions on your sheet

Power = Used Energy (Joules) time (seconds) Calculate the power of a kettle that uses 55 000 Joules of energy in 60 seconds. P = E (joules) / time (sec) P = 55 000 J / 60 sec = 917 J/sec = 917 W = 0. 917 k. W Now you try some

Cost of Operating Electrical Devices: cost to operate = power x used (k. W) time (h) x cost of electricity

Example: a laptop computer uses a 75 W adapter when it is plugged in. Electricity costs 5. 6¢/k. W h. Calculate how much it would cost to operate the laptop for 1 year for 24 hours per day.

Electrical Efficiency Example: a laptop computer uses a 75 W adapter when it is plugged in. Electricity costs 5. 6¢/k. W h. Calculate how much it would cost to operate the laptop for 1 year for 24 hours per day. Given: power = 75 W = 0. 075 k. W time = 24 hours per day for 365 days = 8760 hours cost = 5. 6¢/k. W h

Electrical Efficiency Example: a laptop computer uses a 75 W adapter when it is plugged in. Electricity costs 5. 6¢/k. W h. Calculate how much it would cost to operate the laptop for 1 year for 24 hours per day. Unknown: cost to operate Select: cost to operate = power x time x cost of used electricity

Example: a laptop computer uses a 75 W adapter when it is plugged in. Electricity costs 5. 6¢/k. W h. Calculate how much it would cost to operate the laptop for 1 year for 24 hours per day. Unknown: cost to operate Formula: cost to operate = power x time x cost of used electricity Solve: cost to operate = 0. 075 x 8760 x 5. 6 = 3679¢ ($36. 79)

Example: a laptop computer uses a 75 W adapter when it is plugged in. Electricity costs 5. 6¢/k. W h. Calculate how much it would cost to operate the laptop for 1 year for 24 hours per day. Unknown: cost to operate Select: cost to operate = power x time x cost of used electricity Solve: cost to operate = 0. 075 x 8760 x 5. 6 = 3679¢ ($36. 79)

Electrical Efficiency Try this: Calculate the cost of operating a 1500 W hair dryer to dry your hair for 6 minutes per day for 3 days. The cost of electricity is 5. 6¢/k. W h

Try this: Calculate the cost of operating a 1500 W hair dryer to dry your hair for 6 minutes per day for 3 days. The cost of electricity is 5. 6¢/k. W h Given: power = 1500 W = 1. 500 k. W time = 6 minutes per day for 3 days = 6 min x 3 = 18 min = 0. 30 hours cost = 5. 6¢/k. W h Unknown: cost to operate

Electrical Efficiency Try this: Calculate the cost of operating a 1500 W hair dryer to dry your hair for 6 minutes per day for 3 days. The cost of electricity is 5. 6¢/k. W h Select: cost to operate = power x time x cost of used electricity Solve: cost to operate = 1. 500 x 0. 30 x 5. 6 = 2. 52¢