quick electrical question
 

i am doing a small science experment and always get these two confused. which one is the positive wire and which one is the negative? positive is red and negative is black right?

http://www.nfgx.com/positive.jpg

Yes, usually

is the wire with writing usually the postive?

Depends, I have seen it as positive and negative before. Look among all the markings for a small + or -.

Red is positive, black is negative.
What's the cord for?

If it's from the socket, it's AC power, so there'll be active and neutral.

pull out your digital meter and test the wires, a neg. volt reading means your leads are reversed

....and this a bullshit thread anyway because the picture is displaying 115 VAC line anyway

The picture is from a 12 volt adapter. Since it was only 12 volt i played the guessing game and got it right the 2nd time but the science experiment was a sucess, negative results but a sucess ;) mcbeers are on me!