I think there is confusion here over the bleed off of charge and the rapid discharge via ionisation. I wasn’t able to open any of the cited sources for electrical conductivity of air, but dry air has the lowest ionisation voltage, with it increasing as humidity increases. This is part of the explanation for why people get more shocks in dry climates, whether hot or cold, than in humid or moist climates. A lower ionisation voltage means that it is easier to provoke a spark from your body to another object with a different potential. That does not mean that dry air is a better conductor!
Also, the incidental discharge one gets as surfaces or objects with lower potentials are touched could be described as “charge bleeding”; the voltage on one’s body would not reach the ionisation potential, so there are no sparks to cause discomfort.
I have experienced the cold, dry climate through 3 years working in Antarctica. Although inside temps are around 20 degrees celcius with relative humidity about 5-20 %, depending on whether there was a humidifier in the building or not, outside temperatures vary between about -5 and -55 degrees C. Shocks are a daily source of discomfort until one learns the protective behaviours to avoid them, such as frequent discharge taps on any metal objects that you pass while moving around.
I know exactly diddley about static electricity that isn’t included in a Schoolhouse Rock video.
Kiwi: Would you consider maybe starting a thread “Ask The Person That Worked In Antarctica.” thread? 'Cause really, that had to be pretty far outside most of our experiences.
Air has conductivity, but unless the ionization threshold is reached, the charge is going to remain unbalanced. I picture it as the air being the dielectric in a capacitor. Does an ideal capacitor bleed off when charged and no external forces are present?
No, but air is hardly an ideal dielectric. Vacuum is closer. Ionization threshhold only applies to breakdown; under normal conditions, some charge is going to leak through the air–ambient background radiation is responsible for much of this. At typical static charge voltages around 30-40 kV, that leakage can be not insignificant. Plus, there are other leakage paths, as well. If you have (or can build) a leaf electroscope and charge it up, you will observe the effects of the charge leaking away.
I have a strong physics background and take pride in having an understanding thorough enough to be able to explain general concepts to others lacking in any physics education.
However, I am dismayed to discover that my understanding of this simple thread topic is wrong or incomplete. I consider this a great learning opportunity and would like to see a simple explanation and answer to the OP’s question. So far I’m seeing mostly confusion.
Here is what needs clarifying:
The annoying static spark results from a charge buildup caused by materials rubbing together (as governed by the triboelectric series) True or false? If not, then where does the charge come from?
If the annoying static spark occurs more frequently when the air is dry, this is due to the lower breakdown voltage of dry air as opposed to humid air. True or false?
If #2 is true, then I should be able to measure the same charge (in a suitable way) on a person (having walked across a carpet, etc) whether the air is dry or humid. True or false?
My personal experience is I can feel the discharge when I touch a grounded conductor, even with an object such as a key (ref Q.E.D.'s post #8 above), not as a “pop” but as rippling shock of a momentary current flow. I have never felt this in humid conditions that would preclude a spark. This tells me there is something wrong with the answers I am seeing upthread.
In my opinion, the charge simply does not build up for some reason when the air is humid. Can this be tested?
I’m pretty sure (1) is true, as is (2) [even if it’s only part of the answer]. I’m not sure how we’d measure 3, it reminds me of the problem with the giant thermometer (how are we going to measure it without changing it?). Since we’d be measuring potential, I’m not sure what our reference potential would be.
Q.E.D., can you expand on your background radiation causing bleed statement above, please?
My feeling is that 2 is false, but a quick search with Google hasn’t turned up an easily digestible, smoking gun site/cite. I suspect that the increased humidity leads to a higher conductivity for air, separate from its effect on the breakdown voltage, and that it’s the increased conductivity that leads to fewer electrical shocks.
Sure, it’s the same effect that occurs inside a Geiger tube. Radiation ionizes some of the gas inside, liberating electrons, which are pulled down the voltage gradient to the anode, knocking other electons loose on the way. This creates a path of ionization which acts as a pretty good conductor, allowing a cascade of electrons to flow from the cathode to the anode. In a Geiger-Mueller tube, the conditions are optimal, of course, and at a low pressure which offers less resistance to current flow (as in any gas discharge tube). In free air, I’d naturally expect there to be far less current flow per volt applied, but there will still be some leakage current present across an air gap at static voltages.
I’ve given this topic some additional thought and quizzed a few friends with a great deal of physics knowledge and education and I am standing by my original answer. I feel confident that no spark occurs when the humidity is high because there is no charge buildup in that situation. A simple thought experiment can prove it. If the root cause of spark or no spark was the breakdown voltage of the air rather than the buildup (or lack thereof) of charge, then a discharge would occur even in humid conditions. Why? Because when you reach for that doorknob the distance between your fingertip and the doorknob gets smaller and smaller. At the point where the breakdown voltage is less than the charge buildup (i.e. the air gap gets small enough) a spark will occur. When it’s humid no spark occurs no matter how close your finger gets to the doorknob, therefore there is little or no charge buildup.
A real comic joule, that guy. But what’s he trying to feed us? Fortunately, wheatstone, for which I boyle water. Anoder way of saying, I’m not changing my diode for him, though this will be my terminal post.
I’ve been away for the weekend so I was not reading this thread, meaning I am only just responding now, not that I ignored you.
My experiences in Antarctica are from the mid 80’s to mid 90’s so they probably have a general relevance but questions about climate change and its effects would probably fall outside my knowledge and experience.
I’m of two minds whether to start a thread as you suggest. I probably wouldn’t be able to commit to being able to reply in a very timely manner, as I really only browse the SD when I’m at work, and that also means I generally don’t post much. It was rather quiet at work last week which allowed me to frame my post over some time. This one, for example, has taken about 5 hours to get typed.