intro to energy

ENERGY - in JoulesPOWER - in watts OR J/s = rate of

energy1 watt = 1 Joule/second

•How many megajoules equal 1 kilowatt-hour (kWh)?

1st Law of Thermodynamics

The total energy of a system is constant.

Energy can be “transferred” to a system

by doing work on it.

Energy can be changed from a form into an equal amount of another form.

Total energy = Potential +

Kinetic

ASSIGNMENTS

•Calculate your energy consumption.

•Recalculate adjusting heat down by 2 and cool up by 2 degrees

•https://www.psoklahoma.com/save/

•print or copy results. Due ________

•Energy Math

With a partner

CheckYour work

1 cal = 4.184 J1 BTU = 1.05 kJ

1 therm = 100,000 BTUPower: Power is the rate at which energy is used. (P

= E/t) Unit: Watt

1W = 1J/s

(1Watt = 1 Joule per second)

Temps to knowCELIUS FAHRENHEIT

ROOM TEMPERATURE

25 77

BODY TEMPERATURE

37 98.6

FREEZING POINT OF WATER

0 32

BOILING POINT OF WATER

100 212

MORE EQUILIVANCIES

•1 W = 1 amp x volt

•Work = Force x Distance

•PE = mgh

•KE = ½ mv2

Review of percentages

•ABOUT 10% of the chemical energy stored in gasoline is used to operate your car, the rest is lost in heat energy. If 100 Joules of chemical energy is consumed to operate your car, how many Joules of energy are lost as heat?

•Part / whole x 100 = percentage

•100 / whole x 100 = 10

•100 / whole = .1

•100 = whole * .1

•Whole = 1,000

•1,000-100 = 900 joules as waste

A 100 Watt bulb uses 100 J/sec of electrical energy. If it is 20% efficient,

thenthe bulb converts 20% of the electrical energy into light and 80% is wasted bybeing transformed into heat (ever felt a

hot light bulb?).

What is the example of the First Law of Thermodynamics above?

What is the example of the Second Law of Thermodynamics above?

How much energy, in kJ, does a 75 Watt light bulb use when it is turned on for

25 minutes?

Assume your electric bill showed you used 1355 kWh over a 30-day period.

a.) Find the energy used, in kJ, for the 30 day period.

b.) Find the energy used in J/day.c) At the rate of $.0749/kwh, what will

your electric bill be for this month?

A 100 Watt light bulb is 20% efficienta.) How much energy does it use in 12

hours of operation?b.) How much energy does the bulb

convert to light during 12 hours?c.) Convert total energy use to kWh1 kWh is equal to 3,600,000 joule.

An electric clothes dryer has a power rating of 4000 W. Assume a family does

5 loads of laundry each week for 4 weeks. Assume each dryer load takes 1

hour.

a.) Find the energy used in J and kWh.

b.) Find the operating cost for 4 weeks. Assume cost is $.0758/kWh

Assume you use an air conditioner for a total of 137 days, 24 hours per day, at

a rate of 7.25 kWh per hour. Assume the cost per kWh is $.0825 and 1 kWh =

3400 BTUs.a.) Calculate the total number of kWh

used per year.b.) Determine the cost of air conditioning

for one year.

Suppose your electric lights use 400 watts per hour and average 4 hours per day, every

day for 1 yeara.) How many kWh per year does this

represent? b.) If replacing the lights with a fluorescent bulb would save 60 w pernight, what savings in kWh does this

represent in one year?c.) If the fluorescent bulb costs $18 but lasts

for 10 years, would you consider it a wise investment over incandescent bulbs? Explain.

Transportation energy is costly.a.) Calculate the gallons of gas use just for

going to the supermarket in oneyear if you take 5 trips to the store per week, traveling 7.5 miles roundtrip, and

your car gets 22 miles per gallon.b.) Convert the gallons to kcal/year if there

are 32000 kcal per gallon.c.) What are some of the other energy uses

associated with gettingfoodstuffs to the consumer other than

transportation costs?

FEDERAL LEGISLATION TO KNOW

Environmental Policy Act

Created EPA. Mandates that agencies prepare environmental impact statements. (Used to delay

Keystone Pipeline)

Nuclear Waste Disposal Act

Government’s responsible to provide waste storage facility, but generators’

responsible for cost of disposal