What wire is positive on a table lamp?

A table lamp using AC (alternating current) does not have a positive wire, but many will color-code the wires white and black within the circuit.

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As said, no positive and negative, but there IS a hot and a neutral. The hot wire may have ridges running the length of the insulation (or be colored black if separately insulated). The hot wire connects to the brass colored screw, and feeds power to the base of the bulb. Yes, will work if reversed, but is not according to electrical code. White or unridged wire connects to silver colored screw, which connects to the shell of the bulb base.