electrical efficiency lg: to understand how energy efficiency is calculated & use it to...

Electrical Efficiency

LG: to understand how energy efficiency is calculated & use it to determine energy efficiency of household electrical devices


Electrical Power: the rate at which electrical energy is produced or used.

-measured in Watts (W)-one Watt is equal to one Joule of energy used per second



Electrical Power: the rate at which electrical energy is produced or used.

-measured in Watts (W)-one Watt is equal to one joule of energy used per seconde.g. 100 W light bulb uses four times as much

energy per second as a 25 W bulb.



kilowatt-hour (kWh): the SI unit for measuring electrical energy usage

-1 kWh is the use of one killowatt of energy for one hour-3 600 000 times as much energy as 1 Joule



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

e.g. Clothes dryers-older clothes dryer uses 800 kWh per year-new clothes dryer uses 300 kWh per year-they both do the same job so the new dryer is more than twice as efficient



Calculating efficiency of a Device:

percent efficiency = energy out x 100%energy in



Calculating efficiency of a Device:

percent efficiency = energy out x 100%energy in

short form:


Eout

% efficiency = _____ x 100% Ein


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 JEin = 100 J

Unknown: % efficiency




Given: Eout = 35 JEin = 100 J

Unknown: % efficiency Eout

Select: % efficiency = _____ x 100% Ein




Eout

Select: % efficiency = _____ x 100% Ein

Solve: % efficiency = 35 J_ x 100% 100 J

=35%



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




Given: Eout = 850 J Ein = 1200 J

Unknown: % efficiency

Select: Eout

% efficiency = _____ x 100% Ein




Solve: % efficiency = 850 J x 100% 1200 J

= 71%

therefor the toaster oven is 71% efficient



Cost of Operating Electrical Devices:


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¢/kWh. Calculate how much it would cost to operate the laptop for 1 year for 24 hours per day.




Given: power = 75 W= 0.075 kW





time = 24 hours per day for 365 days= 8760 hours

cost = 5.6¢/kWh




Unknown: cost to operate

Select: cost to operate = power x time x cost of used electricity




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)



Try this: Calculate the cost of operating a 1500W hair dryer to dry your hair for 6 minutes per day for 3 days. The cost of electricity is 5.6¢/kWh





time = 6 minutes per day for 3 days= 6 min x 3= 18 min = 0.30 hours

cost = 5.6¢/kWhUnknown: cost to operate




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¢


electrical efficiency lg: to understand how energy efficiency is calculated & use it to...

Documents

j of energy

electrical efficiency

electrical efficiency

percent efficiency

electrical energy usage

joule of energy

j of light energy

energy output