Electronics > Beginners
Multimeters and Resistors
<< < (13/13)
tooki:

--- Quote from: Kohlrak on November 24, 2017, 03:53:15 pm ---I thought the resistance of my body was too high to have the parallel effect (just like how air doesn't count). But, now that i think about it, it does make sense.  The resistance is still present across the same circuits, but if i can let even the slightest amount of current from that 9v through me, it'll take some of the resistance away.

--- End quote ---
The resistance of your skin varies wildly based on thickness, where on your body, how dry or moist the skin is, how sweaty it is (sweat = salt = ions = lower resistance), how oily it is, etc.


--- Quote from: Kohlrak on November 24, 2017, 03:53:15 pm ---I still do wonder what the threshold for current flow is. In a pure math world, everything's constantly conducting in the slightest amount (too small to measure), but in the real world that's not the case (at least by our understanding). There's a noticeable threshold for when an arch happens and when it does not. Presumably, this should be the case for all materials. So at what current value (according to ohm's law) does current actually flow?

--- End quote ---
It’s the voltage that pushes current flow, and it’s voltage that causes dielectric breakdown and allows conduction to begin across an insulator. That’s why high voltage can jump across an air gap, ionize the air, and produce a conductive path.

I’m no physics whiz, but basically you can consider things to be either conductors (any resistance lower than infinity) or insulators (infinite resistance). For most low-voltage purposes (and certainly the level you’re at), a sort of ballpark is that any resistance up to about 10Mohm is a conductor, and anything much above you can effectively treat as an insulator. Look at the ranges of values that normal resistors come in: from about 1/2 ohm to about 100Mohm: that gives you a decent idea of what is used in most circuits, and even the extents of that are fairly rare. Any resistance below that, we can usually treat as “zero resistance”, and anything above as a de-facto insulator.

Of course, there are specialties where this does not apply (like insulation testing for safety in mains-powered devices, or anything high voltage), but you’re not ready to be doing those things quite yet anyway. :)



As for color bands: I can’t emphasize enough how important the light source is. You need lots of light, and it needs to be good quality, as others have said. A little halogen desk lamp can be a lifesaver in this regard.
Navigation
Message Index
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod