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

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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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