PDS AP Environmental Science 8th Period 2010-11

1) Energy and Power Calculations

E=P x T   (that’s   Energy in Joules= Power in Watts multiplied by Time in time units   )

Like wise   P=E/T

example: How much energy (J) does a 30 W bulb use if on for 10 minutes?            E=PT  —>  E=30W x 10 minutes x 60 seconds

E=18000J

2) Heat Transfer Calculations

Q=m x c x delta T

(that’s    Amount of heat energy in calories or BTU= mass in grams or lbs x specific heat of water (generally 1) x change in temperature in degrees C or degrees F)

3) Cost Basis

Units Used x Price/Unit= Price

4) Efficiency

Input of Energy= output/efficiency as a decimal

Let’s say a 60W bulb is 5% efficient —>       60W=X/.05  —>    60(.05)=X  —> X=3W to light

Here is a list of common efficiencies: Incandescent=5%, CFLs=20-25%, Coal Power Plant=30-35%, Nuclear Plant=25%, Car Engine=20-25%, Photosynthesis=1%

http://www.richmondhill.ca/subpage.asp?pageid=epw_energy_efficiency_open_house

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