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.

 

[charng]

I can provide a response to this content by explaining the concept of energy conservation in circuits. First, it is important to understand that energy cannot be created or destroyed, it can only be transferred from one form to another. In the case of an electrical circuit, energy is transferred from the power source (such as a battery) to the components of the circuit (such as resistors or LEDs).

Now, when we talk about no net energy input to the circuit, it means that the total energy input from the power source is equal to the total energy output from the components. This is known as the law of conservation of energy. In other words, the energy entering the circuit from the power source must be equal to the energy consumed by the components in the circuit.

In the case of a simple resistor and LED circuit, the LED will indeed light up and consume energy. However, this energy is not lost, it is simply converted into light energy. So, while it may seem like there is a net energy input to the circuit (since the LED is consuming energy), in reality, the total energy input and output are equal.

The statement about no net energy input to the system refers to the overall circuit system, including the power source, components, and the connecting wires. In an ideal circuit, where there is no resistance in the wires, the energy input and output would be exactly equal, resulting in no net energy input or output to the system.

In summary, the concept of no net energy input to the circuit is an important principle in understanding the behavior of electrical circuits and is based on the law of conservation of energy. It is not affected by the presence of components that consume or dissipate energy, as this energy is simply converted into other forms.