Conserve Energy: No Net Energy Input to Circuit

[prof]

I read from http://www.facstaff.bucknell.edu/mastascu/eLessonsHTML/EEIndex.html the following:

"If we move the charge through any closed path or circuit, there will be no net energy input to the system and no net energy recovered from the charge."

If we have a simple resistor and LED circuit, we know that the LED will light and thus use energy. Now I can understand the statement that the net energy will remain in the "system" depending how "system" is defined. But how is it that " there will be no net energy input to the system" where I consider system to be comprising of a closed circuit. Or is it that the author is trying to mention circuit as being ideal with no load attached (i.e, ideal wire attached to terminals of ideal battery).

Thank you for your help.

 

[Doc Al]

This is just saying that whatever energy is supplied by the battery or voltage source will be dissipated by the circuit elements--be they LEDs, resistors, or light bulbs. So if you trace a path around the circuit, keeping track of the voltage drops, you will end up with no net gain.