A steady brightness
Physics Narrative for 14-16
Thinking carefully about a steadily glowing lamp
A lamp glowing steadily is shifting energy at a steady rate. In a simple circuit, where the wires connect one lamp to one cell, energy is being shifted to or from stores at two places: the lamp and the cell. The same change is calculated at both: energy is shifted from the chemical store associated with the cell, and to the thermal stores around the lamp. That the change is the same seems like too much of a coincidence for there not to be a strong connection, and, of course, there is. The wires make the physical connection (there is a similar connection in the energy description). The same electrical working empties the chemical store and fills the thermal stores. This is what electric circuits are good at: connecting stores so that we can arrange the rates of depletion and accumulation.
Electrical working is the pathway that empties the chemical store at a calculable number of joules/second or watts. Electrical working is also the pathway that fills the thermal stores at the same rate. This power in this pathway is a constant number of watts. It is the link between the stores.