The atomic number of uranium-235 is 92, its half-life is 704 million years and the radioactive decay of l kg of 235U releases 6.7X10^13 J. Generally, radioactive material is considered safe after 10 half-lives.

Assume that a nuclear powerplant can convert energy from 235U into electricity with an efficiency of 35%, the electrical transmission lines operate at 90% efficiency, and flourescent lights operate at 22% efficiency.
1.) What is the overall efficiency of converting the energy of 235U into flourescent light?
2.) How much energy from 1 kg of 235U is converted into flourescent light?

Question

The atomic number of uranium-235 is 92, its half-life is 704 million years and the radioactive decay of l kg of 235U releases 6.7X10^13 J. Generally, radioactive material is considered safe after 10 half-lives.

Assume that a nuclear powerplant can convert energy from 235U into electricity with an efficiency of 35%, the electrical transmission lines operate at 90% efficiency, and flourescent lights operate at 22% efficiency. 
1.) What is the overall efficiency of converting the energy of 235U into flourescent light?
2.) How much energy from 1 kg of 235U is converted into flourescent light?

anonymous · Answer

To find out the overall efficiency, multiply each percentage expressed as a fraction of 1, then once you've done that multiply by 100 again to get back to a percentage value. I think that if you multiply the overall percentage efficiency by the total energy from 1kg of U235 you'll have your answer. If you want to check your answer I can work it out and see if we agree.