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Q & A: energy and electrical current

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Most recent answer: 04/24/2016
Q:
I have a few questions, but I dont know if they are silly. First, when a bulb glows its releasing energy in the form of light and heat. What causes this? Is it flow of electrons? If then why do some objects glow and others dont even if they have more resistivity? Second, if electrons themselves dont get consumed or annihilated, and they flow around the circuit, why do we have to supply current all the time or why do we need to keep a potential difference? Why are superconducting materials said to have indefinite current without a source? Dont we have to supply a potential difference across it?These are some doubts I had. I will be glad if anybody helped me with it.-Diyah
- Diyah (age 15)
India
A:

As the electrons flow through the filament, they bump into things (mainly sound waves but also crystal defects) and transfer energy to them. So the wire gets hot. How much the wire glows depends mainly on how hot it is but also on how easily it exchanges energy with light waves. The same things that easily absorb light energy (and thus look black) also easily emit it when they're hot.

You need some voltage to keep pushing those electrons because otherwise the same collisions where they lose energy cause the flow to run down quickly. The voltage accelerates them so that you keep getting a current.

Superconductors are special because they have almost no way for the electrons to dump energy to sound waves or anything else. That means that the current in a loop just keeps going without needing any voltage push. Depending on how things happened to start off, there could be a whole range of different currents with no voltage.

Mike W.


(published on 04/24/2016)

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