- #36
Edison Bias
- 105
- 5
Tazerfish said:1.Some charges can flow onto the the handle, without directly flowing away.It essentialy acts like a capacitor.
Charges cannot easily flow into the door, since it is a poor conductor.
I like this explanation, a wooden door is like a capacitor with a dielectrica (high resistance, some permitivity) and the doorknob is one of it's plates.
The door area the doorknob touches is not much but it's a good conductor and the dielectrica/door is in parallell which makes up for some capacitance to ground.
So you are standing there with some strangely accumulated amount of charge and therefore potential due to walk on a carpet and you touch the doorknob with a total different potential (remember, it is clear now that the pure amount of charge does not tell the potential).
If
[tex]i=C\frac{du}{dt}[/tex]
Then discharge current is only limited by rate of voltage change which in this case should mean rate of "potential difference change" which is only limited by the total resistive path of Kirschoff Voltage law. If door-knob plus wooden door is the capacitance to ground, the carpet you are standing on, your shues and your body is the resistive path. So the resistive path limits the current but it does not limit when a discharge should strike because that is purely determined by potential difference and dielectric strength (of air).
Now, can we use this within a cloud? The dielectrica may be moistured air. Clusters of charges of different sign have somehow been built up on both sides of this moistured air. At a certain point in time, these clusters (or plates, actually because they are highly conductive) of charge comes so close together that the E-field exceeds the dielectric strength (V/m) of the moistured air and a discharge/lightning happens.
Okey, this is "my" rough theory but what about the details? I.e how does these charge gradients emerge in the first place and why and how do they accumulate?
One theory has been that friction is important (from davenn), friction between droplets and ice chrystals, this may explain charge separation but why accumulate?
Another interesting theory has been (from Tazerfish):
Maybe because the droplets are often supercooled (i have no source for that) they will freeze a little upon contact with an snowflake or ball of hail, which might push out ions at different speeds causing some to be captured more in the ice than others.
So we have some explanations for charge separation but they are still very vague, and no good explanation for charge accumulation (not even generally).
I do however promise to read some more of your nicely provided links before I utter a single more ignorant word :)
Edison