I have some questions about potentiometers

[foos-it]

How do I define which lug is 1, 2 (middle I assume), and 3? I am familiar with linear and audio pots, but what is a log pot?

foos-it

[Govmnt_Lacky]

A log pot is the SAME as an audio pot.

Taper A = Log or Audio
Taper B = Linear
Taper C = Reverse Audio or Reverse Log

90% of layouts/schematics you find (NOT ALL) will use the following format for lug numbering:

With the pot upside-down (pot shaft facing away from you) and the lugs downwards, they number from 1 to 3 going from right to left.

Good Luck 

[Mark Hammer]

Yes.  "Audio" is not related to sound quality or anything regarding its suitability for audio signals vs other kinds.  It's called an "audio" taper because most human senses demonstrate a near logarithmic response curve; i.e., it takes increasingly greater and greater amounts of change in the physical stimulus to be perceived as a change.

When you get lost in the flipping back and forth and numbering, just remember that "louder", or "more" nearly always implies the wiper moving towards the input (thereby reducing the resistance between them).

So, if the shaft is pointing towards you, and the lugs are pointing down, the "input" is on the right, the ground on the left.  As you rotate clockwise, the wiper moves towards the input lug.

[Hides-His-Eyes]

Ignore numbering on any layout without a diagram and always think through what you want to happen when the wiper goes clockwise.

[Gurner]

Just rest assured that no matter how much you plan to get the lugs around the right way, chances are once you've actually wired it up, it'll work in reverse to what you wanted! Therefore unless your POT is going to go on a PCB (when it therefore has to be correct), just be prepared to swap the outer lugs around!!

[petemoore]

If you can't find the graphs, useful, audio taper looks like a bowed line from L/bottom corner to R/top corner of the graph square, sort of like a straight line that got pulled toward the right bottom corner.
  Linear pot, graphed, shows a straight line from L/bottom to R/top corners, diagonal across the square.
  One way to tell, 92k pot as example, set for 41k/41k right in the middle of R sweep, a linear pot would put the knob pointer at 12 oclock, the audio potknob pointer might be at 3 oclock...''all'' the change in resistance is 'bunched up' at one end of the potshaft rotation range.

[thetragichero]

pots are one reason i breadboard first... i always hook up the outer lugs the wrong way!

[bassesofdeath]

If the project or circuit bill of materials calls for an A100k, what effect will using a C100k have on the circuit?

[joegagan]

put down the crayons, son! ( ha, i don't know what it means but i do love it.)

[ACS]

put down the crayons, son! ( ha, i don't know what it means but i do love it.)

Dat dere's a burst box... I knows one when I sees one 

[Galego]

If the project or circuit bill of materials calls for an A100k, what effect will using a C100k have on the circuit?

If used in a volume control, if you use a linear potentiometer (B100k), you'll feel that the sound increases quickly as you turn the knob and the rest of the travel does nothing. Using a C100k will worsen that.

[boogietone]

If the project or circuit bill of materials calls for an A100k, what effect will using a C100k have on the circuit?

If you wire it up with the same lugout as the audio pot, you will likely be cursing yourself asking why does this thing only work for 10-20 degree of turnage.