Thermodynamics: conservation of energy

[mbm]

Homework Statement

Suppose you left a 100w light bulb on continuously for one month. If the electricity generation and transmission efficiency is 30%, how much chemical energy (in joules) was wasted at the power plant for this oversight? if the fuel consumption for one meal in China using kerosene wick stove is 6MJ, how many equivalent meal could you be obtained with this wasted energy?

Homework Equations

The Attempt at a Solution

My first thought was to convert the W to J, however after that I'm kinda stuck since the efficiency given is the overall.

 

[tiny-tim]

hi mbm!

watts are power, power times time is energy, so watts time seconds are joules …

and if the power company is 30% efficient, how many joules does it have to use to produce one joule at your home?

 

[mbm]

thnx :P