posted by Anonymous .
A 46% efficient device uses chemical energy to generate 570J of electric energy.
1. How much chemical energy is used?
2. A second device uses twice as much energy to generate half as much electric energy. What is its efficiency?
1. Eff. = Eo/Ei = 0.46.
570/Ei = 0.46
Ei=570/0.46 = 1239 J. = Chem energy in.
2. Eff. = 0.5Eo/2Ei = 0.25(Eo/Ei).
Replace Eo/Ei with 0.46:
Eff. = 0.25*(0.46) = 0.115 = 11.5%.