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# Physics/Energy efficiency of different energy sources

Question
Hi! I was reading up on the energy efficiencies of different energy sources. The highest was fusion with 0,7% of the mass turning into energy and fission following up with 0,1% as the second. So if even the most efficient energy production methods are less than 1% efficient, how efficient for instance are:
a) Gasoline
b) Coal
c) Gas?

This question is easier for you to answer by comparison.  Energy density listed for uranium (I checked, it's legitimate) is 80,620,000 MJ/kg.  Gasoline is listed as 46 MJ/kg, so a far lower percentage indeed.  Gas is about the same, coal is about half that (depends on the grade).  So if you want some percentage in terms of mass conversion to energy (which doesn't make much sense, given how low it would be, and you're considering fission to be 0.1%, then you can use these numbers to convert (multiplying by the energy density and dividing by uranium for your standard).  I'd tell you to just use E=mc^2, but people usually convert the units wrong.  For reference, see http://en.wikipedia.org/wiki/Energy_density

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.