Electricity

[Whoo-hoo]

What happens to the electricity that goes into a lightbulb, if it get's used up by turning the bulb white hot, why do you need a return path? �what goes back

[JustSia]

The electricity doesn't actually get used up as such. It's continuous flow heats up the filament, which in turn emits light.

Have a look at this.

http://en.wikipedia.org/wiki/Light_bulb

S.

[mibn2cweus]

Electricity is the flow of electrons. What you need for light is photons. The light produced by a light bulb is a secondary consequence of the electrical current flowing through the resistance of the filament. Heat generated in the filament (by forcing electrical current to flow through it) causes the filament to radiate photons. Excess heat generated in the filament is carried away with the emitted photons.

The trick is to get the electrical current to flow through the resistance of the filament. This requires force. (light bulbs have to work really hard to make light).

Electrons flow much easier in a conductor. such as a wire, made of a metal that has loosely held electrons. This serves as a medium for the transfer of electrical current.

To get current to flow into the filament you need to provide a way for it to flow out at the other end.

A source for electrical current is a battery or generator. These power sources provide a potential surplus of electrons at one terminal and a deficit of electrons at the other terminal.

This imbalance is a force analogous to the water held behind a dam. To get the water to flow to the lower level on the other side you need to provide a path. You could place a turbine in the path of this water and extract power from the flowing water.

By inserting a light bulb in an circuit connected to both terminals of an appropriate electrical power source . . .

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[Whoo-hoo]

Thanks all, I don't think I made myself clear enough though. What i wanted to know is more to do with circuit theory, -I'm bemused as to what actually goes back on the Neutral conductor.

assume the voltage is used up by the device, but if that's the case there's no "push" left , -so how come anything travelles back on the Neutral. Can you have current at 0v?

Thanks all.

[qapmoc]

Think of it like a waterwheel, the water flows past the wheel and does work and the water slows down due to the lost energy but the same amount of water is still there. The same is true of electricity, it makes heat+light and at the end there is a lower amount of energy left but the same amount of electrons have to pass around the circuit.

[Whoo-hoo]

Ah, I think I get it, so there's very little voltage, but still current, -is that right?

[mibn2cweus]

Voltage is not a physical substance but rather a measurement of the force that causes a physical substance, current, (the flow of electrons) to move through the circuit. This force (voltage) is created by an imbalance of electrons which seek to maintain equilibrium when a path for doing this is provided.

When we measure voltage we are measuring the difference in potential force between two points. A potential difference in force (voltage) is created in a battery or by a generator. As current flows through a resistance a potential difference of opposite polarity is created equal to the surplus of electrons seeking to find their way through that resistance. In a resistive circuit the sum of all voltage drops (caused by electrons seeking to maintain equilibrium) exactly equal (offset) the sum of voltage rises (potential differences created by a battery or generator).

The rule is, �In a circuit consisting of only resistance and a constant voltage source, the sum of voltage rises and drops equal zero.�

For a given voltage, current is inversely proportional to resistance. As resistance increases current decreases if the voltage remains constant. The resistance of a light bulb filament actually increases as it heats up. This results in a decrease of current through the filament. At a certain temperature the current and resistance become stable.

[Whoo-hoo]

Blimey that's brilliant. Best description ever. I've had real problems trying to "get" the idea of a return path with no potential difference, and no current.

I guess that's why Neutral is tied to Earth at the unit, they're both 0v reference. -Can you actually measure anything on a Neutral referenced to Earth?

[Zevon]

Thi si one of the very rare cases when the water analogy of electricity doesn't quite work.

well done mibn for for getting to the nitty gritty of electricity.