pilot operated valve?
with "gate" pressure the same source as mains pressure.

Russell McMahon wrote:
> I'm looking for a "metaphor" / model / description that allows me to 
> easily explain a typical LED current/voltage curve to a layman in a 
> manner that isn't just understandable but which is so intuitively good 
> that it 'binds to the brain' as an explanation when we subsequently 
> discuss matters which depend on this characteristic.
>
> An LED has an exponential increase of current flow with forward 
> voltage. Below a certain voltage it is for practical purposes non 
> conducting but apparently "rushes into conduction" exponentially above 
> a certain voltage.
>
> The mechanical/hydraulic model need not be perfect - just model well 
> enough to allow intuitive grasp the *apparent* essentially zero 
> initial current and exponential current with voltage behaviour above a 
> certain threshold.
>
>
>
>         Russell
>
> ________________________________
>
>
>
> For many years I've had good enough mechanical / hydraulic metaphors 
> for eg
>
> Resistor - water pipe of given bore and roughness.
>
> Capacitor - tank with variably elastic diaphragm separating input and 
> output sections.
>
> Inductor - air dome
>
> DC energy source - pump
>
> AC energy source - double sided hydraulic piston driven appropriately 
> with no path between sides
>
> Battery - dam with pipe outlet tapped off below surface
>
> None of these metaphors is perfect but they are extremely useful in 
> explaining basic electrical concepts.
>
> __
>
>
>
>   

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