General Question

julia999's avatar

Is current used up when it goes through a light globe?

Asked by julia999 (343points) April 8th, 2010

I am studying physics about how current is basically the flow of charge carries through a conductor. But I was wondering, is current actually used up, say, when it goes through a light globe?

How does the light globe turn on without charge carriers losing their charge to power it?

Thanks in advance

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8 Answers

Rarebear's avatar

Electron energy is converted to light and heat in the resistance of the light globe.

CaptainHarley's avatar

It’s just a tad more complicated than that. Every device which draws electricity, including lightbulbs, darws from the grid only that electricity it requires to operate. In the cse of a lightbulb, the blub draws what electricity it needs for light and heat. The rest remains in the grid, which, by the way, is the total system of interrelated electrical connections, transformers, generators, etc. for the continent ( in the case of North America ).

julia999's avatar

Okay, so current is lost, but only as much as a load needs?

julia999's avatar

(where a load is a light bulb or other device that transforms electrical energy into some other form of energy)

jerv's avatar

Not quite. It takes as much as it needs plus enough to cover losses and inefficiencies.

Light bulbs are supposed to just generate light but also generate a considerable amount of heat. Modern CFL bulbs run cooler than old-school incandescent bulbs since they are more efficient and thus can generate the same amount of light on less than ⅓ the energy input.

The voltage is set by whatever power source you use, in this case it’s the power grid.
The amperage is determined by the resistance of the load; I = E/R, where I = current (in amps), E = Voltage, and R = Resistance. No more, no less.

When buying a power supply or charger or figuring out what sized fuse/circuit breaker to use, the amperage rating is a maximum it can provide. It won’t push the amps in there; the load will only take what it needs.

But the important thing here is that the current is not lost; it’s converted.

julia999's avatar

Thank you very much Jerv, that makes so much more sense to me now :)
Energy can’t be lost (law of conservation of energy) but it is lost from the circuit when it is transformed into other things.

CaptainHarley's avatar

Never said it could be “lost,” just that the device draws as much power from the grid as it needs to operate.

jerv's avatar

@CaptainHarley I knew what you meant, but as you said, it’s complicated. However, you were correct and still are.

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