Hi all: I am just starting Circuit Theory and am taking Physics 2 concurrently. As such, I am new to many of the subjects and terminology used in the book I am using and am finding reading it quite a challenge (For those interested, it is The Analysis & Design of Linear Circuits by Thomas/Rosa/Toussaint). Anyway I am having trouble figured out a particular problem on our first problem set: 1-14: An incandescent lamp absorbs 100 W when connected to a 120-V source. An energy-efficient compact fluorescent lamp (CFL) producing the same amount of light absorbs 16 W when connected to the same source. How much cheaper is it to operate the CFL versus the incandescent bulb over 1,000 hours when electricity costs 7.8 cents/kWh? My main issue here I suppose is the concept of kWh. Is this kilowatts absorbed per hour? If that is the case, why does the voltage of the source matter? I am sure I will visit this page often throughout the semester! Thanks.