I came across this question about how to figure out the polarity of a cell phone charger without a meter. This made me think of what methods you could use to figure out the polarity other than using a meter or any device that is better than a meter; and I thought it would be an interesting question for my first question here.
My answer was that you could use a LED or a diode to figure it out. Or you could use salt water, as long as the voltage is high enough (over 2 volts, I think,) you could place both leads into heavily salted water and the negative lead will produces more bubbles and corrode faster.
Another ideas I thought of would be to use a linear regulator and see if you destroy it (testing if you destroyed it would require a meter or at least a circuit where it was working originally.)
What other ideas/options can you think of? Like electromagnetic methods or even blowing up capacitors...
As @Juancho pointed out, when I said without a meter I meant without a multimeter (or a more advanced device.)
Since this is basically a thought experiment, feel free to make the voltage and current whatever you want, but try to point out the range if it matters. For example @DeanB's neon answer required ~70 volts.
There are some great answers so far, thanks everyone! I'm sure there must be more basic chemistry options, unfortunately I never took chemistry in school.
Building a meter is also a valid answer. In fact there really isn't a wrong answer, other then saying, "use a multimeter."
This is becoming quite cool, some very interesting and unique answers! Thanks everyone!
I found this elsewhere and thought it was interesting, however @Juancho already posted a similar answer.
How MacGuyver might find out:
- some insulated wire
- a compass
- a suitable resistor
- a stick of chewing gum
- a pencil
- Wrap the wire around the pencil 20-30 times. Looking at it from the eraser end, the wire should be going around counterclockwise.
- connect wire #1 of your adapter to the clockwisemost end of the coil (still looking from the eraser end). In series, connect the resistor to the other end of the coil. Connect the other end of the resistor to adapter DC wire #2.
- chew gum (save the wrapper in case you need to defuse a bomb later in the afternoon)
- plug in the adapter
- hold the compass near the eraser end of the pencil 6) if the compass points toward the eraser end, #1 is the negative wire. If it points away, #1 is the positive wire.