ENERGY. TYPES OF ENERGY Kinetic - energy in motion Potential - stored energy Chemical - energy stored in the bonds of molecules and atoms Nuclear energy- energy stored in the nucleus of atom Electrical energy- electrons moving through a wire
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percentage of energy input that does useful work in an energy conversion system
When we’re energy efficient we use less energy to do something as good as before or better. We have to remember there is a limited amount of non-renewable fuel sources such as coal and gas. Even if we don’t run out of fuel, we can damage our environment by using too much and wasting energy.
Energy transformations are great, but very inefficient! Our bodies are about 20% efficient, and burning the gasoline in your car is only 10% efficient! Most of the energy is lost in the form of heat!
Efficiency of Some Common Devices bodies are about 20% efficient, and burning the gasoline in your car is only 10% efficient! Most of the energy is lost in the form of heat!
Device Efficiency (%)
Knowing the relationship between energy and power allows you to find the energy used when an appliance of known power (watts) operates for a known amount of time.
1. A.) 100 kg x 1kcal x 20 `C = 2,000kcal
B.) 2,000 kcal x 4.186j x 1,000 cal= 8.37 MJ
C.) 1Btu x 8.37 x 106J = 7934Btus
D.) 7,934Btu x 1h x 60m = 11.9 min
2 bulbs for 1 hour.. A.) 1KWH x 3.6 x 10J x 1BTU = 3,412BtuKWH 1,055J
B.) The second law of thermodynamics prevents 100% conversion of heat to mechanical or electrical energy. A typical coal fired plant operates at 33% efficiency, meaning that only 1/3 of the energy in coal is converted to electricity.
3.A bulbs for 1 hour..
120MBtu x 1,000,000 = 1.2x10 Btu x 1 ft3 x 1/ccf= 1,165ccf (gas)
1 MBtu 1030Btu 100ft3
B. 1165ccf = 1,942ccf x $0.9 = $1,748 to heat house@ 60% eff
C. 1165 = 1456.25 ccf x $0.9 = $1,310.6 to heat house@ 80% eff
Money saved per year in heating costs = $1748-$1,310.6 = $437.40
Years to payback cost of furnace = $4000/$437.40 = 9.1 years
4.A.) bulbs for 1 hour.
8760hrs/yrx 160 W/m2 x 10m2x .20 =2,803.2 KWH
2,803.2 KWH x 3.6x106 J x 1BTU = 9,565,421 BTU = 9.57 MBT KWH1055 J
B.) 2,803.2 KWH = .2803 =28%
9,565,421 Btu = 1,200 BATHS
5.A.) bulbs for 1 hour.250 W/m2 x 10m2 x .10 x 1KW x 8,760HR = 2,190 KWH
B.) 2,190 KWH = .219 x 100 = 21.9%
C.) 10,000KWH x 10m2 = 45.6621m2
6. bulbs for 1 hour.8,760 x 200W/m x 106m x .001 x 3.4123 Btu = 498 Tons
12 X 106 Btu/ ton W
7A bulbs for 1 hour..) 1,000MW x 1,000KW
MW = 4,000 Wind Turbines
B.) Solar energy can help to decrease the total amount of energy provided by the power company by 21.9 %. Solar energy used to heat water could be feasible for small families. It would not be economical or practical to use solar energy as your only energy source at this time. Wood is very inefficient as a heat source. The forest in example 7 could provide enough energy for almost 50 homes. The trees would require continuous replenishment; the soil would require fertilization to maintain……
8.) Battery: bulbs for 1 hour. 4.5 WH = .0045KWH
1 = $222.22 / KWH
9. bulbs for 1 hour.
Natural gas cost is $1.14x 1cf x 1 ccf = $11.07/MBTU
ccf 1030 BTU 100cf
120/.8 x $11.07 = $1660.50
Propane gas cost:
$1.69 x 1 gal x 1x 106 BTU = $18.37/MBTUGal 92000 BTU MBTU
120/.8 x $18.37= $2775.
Fuel Oil cost: bulbs for 1 hour.
$1.93 x 1 Gal x 1x106 BTU = $14.51/MBTU
Gal 133,000 BTU MBTU
120/.8 x $14.51= $2177
0.10 x 1KWH x 1 x 106 BTU = $29.51/MBTU
KWH 3412 BTU MBTU
120/.8 x $29.51 = $3,517
1. Dr. Jones’ Nov-Dec power bill shows that his home used 1355 kwh over a 30 day period.
A. 1355 kWh x 3600kJ/1 kWh = 4878000kJ bulbs for 1 hour.( 4.9 e 6 kJ)
B. 1355 kWh/30 days x 3600000 J/1kWh = 1.6e10 J/day
C. 1355 kWh x $0.0749/kWh = $101.49
2. The current through a toaster (110 V) is 8 amps bulbs for 1 hour.
the toaster use in 5 minutes of
880 J/sec x 60 sec/1 min x 5 min = 264,000 J
3. A 100 watt light bulb is 20% efficient. bulbs for 1 hour.
bulb convert into light over the
12- hour period?
bulb convert into heat over the
A. 20 J/sec x 60sec/1min x 60 min/1 hr x 12 hrs = bulbs for 1 hour.
B. 864,000 J
C. 80 J/sec x 60 sec /1min x 60min/1hr x 12 hrs= 3,456,000 J
D. 4,320,000 x 1kwh/3.6e6J = 1.2 kwh
4. An electric clothes dryer has a power rating of 4000W. Assume that a family does 5 loads of laundry each week for 4 weeks. Also assume that each load takes 1 hour.
B. If the cost of electricity is
$0.758/kwh, find the cost of
operating the dryer for 3 months.
B. 80 kwh x $0.0758/kwh = $6.06
5. Dr. Nick’s natural gas bill states that his household used 110 therms of energy for a 30-day period.
was $88.78. Find the cost
of this natural gas in $/kwh.