# Physics

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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?

• Physics -

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%.

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