This reminds me of the old trick to detect the polarity of the ignition coil on an engine, using a pencil.

Don't forget to cook and eat that potato!

Ah I thought this would be a new take on that apocryphal bayesian story

>An engineer draws a random sample of electron tubes and measures their voltage. The measurements range from 75 to 99 volts. A statistician computes the sample mean and a confidence interval for the true mean. Later the statistician discovers that the voltmeter reads only as far as 100, so the population appears to be 'censored'. This necessitates a new analysis, if the statistician is orthodox. However, the engineer says he has another meter reading to 1000 volts, which he would have used if any voltage had been over 100. This is a relief to the statistician, because it means the population was effectively uncensored after all. But, the next day the engineer informs the statistician that this second meter was not working at the time of the measuring. The statistician ascertains that the engineer would not have held up the measurements until the meter was fixed, and informs him that new measurements are required. The engineer is astounded. "Next you'll be asking about my oscilloscope".

Sometimes low-tech works best can litterly save your life. This kind of reminds me how you can start a fire with a watter bottle [1].

Good job MTA @ diy.stackexchange.com for recommening this and jasonhansel @ HN for posting it.

[1] https://www.youtube.com/watch?v=QwQJ-3pZfwc

I remember this from the old 'potato clock' science kits from the 80s. They had a copper cathode and zinc anode that when inserted into a potato (most fruit/vegetables or acidic liquids also worked) generated enough power to run a small LCD clock. In a potato, the copper cathode always left a green spot.

Can anyone explain what's really happening here? Why green? Why potato?

Great potato story. Loosely related story here. My late grandfather in Belarus (the land of potatoes) loved potatoes just like everyone around. Well, he was an electrician at the concrete/brick making factory for entirety of his career, from right after the war until he retired in the late 80ies. The amount of electricity used to fire the kilns for bricks is well known to be huge. He said that they'd see the rats scutter along the power lines on the wall and every once in a while they'd touch the rails wrong and disappear in the scintillating disintegration. Oh, and he let me weld random junk together with his own cobbled together electrical welding kit when I was like 8, oh I loved that so much. I miss him.

How dangerous is this? Just thinking about working with live wires makes me nervous.

"Do not allow the bare wires to touch each other from this point on."

What happens if they touch? Note that this is while the adapter is unplugged, before sticking the wires into the potato, so shorting them isn't a concern. I can't really imagine that some kind of contamination is a problem since both wires are (probably) copper, nor would I expect any kind of reaction as long as it is unplugged.

Another neat trick in the same ballpark (but not involving a potato :-p) is to create a 220v to 110v adapter with a "resistance bridge".

Plugging two (hopefully pretty equal resistance) incandescent lights in series, each lamp should have a 110v potential difference... say:

A ----(60W lamp)-- B --(60W lamp)----- C

By plugging A and C "cables" to a 220V electrical outlet, one should be able to grab 110V from either A-B or B-C :-) (assuming both lamps have about the same resistance). Most electronic devices work with a wide range of input voltage any way, so it doesn't have to be extremely precise.

The best touch in that story is how the poster works around the lack of a voltmeter by assuming the OP possesses a soldering iron and the skills to use it.

Potato? Who needs a potato? A glass of salt water will suffice.

Just put the wires at some distance in the salt water and look. The wire emitting the blueish fog (chlorine) is the positive, and the one emitting bubbles (hydrogen) is the negative.

Seems to be like the answer is making fun of the question which is pretty easy to answer with very simple and cheap tools.

The level of cleverness and resourcefulness is impressive. To the point that it seems magic or makes me suspicious. I guess this is how the layman feels about instructions to delete System32 to add more RAM.

There should be a step somewhere there that says "don't hold potato with hands while it is plugged"