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# Energy conversions

Various energy forms convert into one another, and when they are measured in various units, the rate of conversion is always fixed. In the conversion process, energy is transferred. Thus, energy conversion covers these areas:

• Conversion factors
Conversion Factors
1 J = 1 coulomb-volt = 1 N m
1 cal = 4.184 J
1 eV = 1.602e-19 J
1 MeV = 1.602e-13 J
1 eV/molecule = 23045 cal/mol
1 amu = 1.66043e-31 J
= 931.4812 MeV
1 atm L = 101.3 J
1 joule = 1e7 ergs
1 BTU = 252 cal
Some units and conversion factors for energy are given here. These are given on pages v and 26 of On Nuclear Technology.

More detailed conversion factors are usually given in handbooks.

• Power - the rate of energy transfer
If the amount of energy E is transferred in the period t, then the power P is P = E / t (1 watt = 1 J s-1). A 12-V battery has a 100-A maximum current output. Its maximum power is then P = 12 V * 100 C s-1
= 1200 watt (1 h.p. = 745.7 watt)
= 1.6 h.p.

Kilowatt-hour is actually an energy unit:

1 kilowatt-hour = 1000 J/s x 3600 s
= 3.6e6 J
= 8.6e5 cal or 860 kcal.

• The Law of conservation of energy
Energy converts among various forms without any loss or gain. Energy is the currency of changes, and money is the currency of exchanges. Which is conserved and which is not? Explain!

Please give an example that is contradiction to the law of conservation of energy.

• Technology for energy conversion
• Nuclear reactors convert nuclear energy to thermal and then electric energy
• Nuclear fusion reactors are still in experimental stage, but they are used to convert fusion energy to electric energy
• Batteries and fuel cells convert chemical energy into electric energy
• Audio and visual equipment converts electric energy into heat, E.M. radiation, and sound energies
• Electrolyses convert electric energy into chemical energy
• Technologies for harvesting solar energy
• Technologies for harvesting wind and tide energy
• Motors convert electric energy into mechanical energy, and generators reverse the process
• Hydroelectric technology
• Heat transfer
• Heat pumps and air conditioners
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E-mail: cchieh@uwaterloo.ca