you need
  • - a solution of salt and nitrate;
  • - potato;
  • - candle;
  • - reagents for the indicator.
Guide
1
Inspect the power supply housing.Near clamp positive contact must be applied "+" negative - "-".In that case, if the sign stands near the source of the clip, the second count with the opposite sign.
2
If the power source there are no signs to accede to two copper wires.At work necessarily work only with the insulated surface to avoid electrical shock.In a glass of warm water, dissolve a tablespoon of table salt (sodium chloride).Immerse the wire.From the conductor connected to the negative pole, the gas bubbles will rise.
3
These plug the wire at a distance of about 1.5 cm from each other in half a freshly cut raw potatoes.Leave structure under tension for 10 mi
nutes.Around the positive electrode (connected to the positive pole) potato begins to turn blue.This method is suitable for determining the polarity of power up to 60 W.
4
Heat two conductors connected to the power supply for the tribe candles.On the negative pole will settle soot.
5
To make an indicator to determine the polarity of the power source, take the glass tube with a diameter of 10-15 mm, two plugs and electrodes from the burnt-out bulb.Electrodes insert the plugs so that they came from two sides.Plug tube with one hand stopper electrode.Fill to this composition: 1 part of ammonium nitrate, 4 parts water, then a solution of 0.1 part of phenolphthalein 1 of the ethyl alcohol and add 5 parts of glycerol.
6
All of this mix.Plug the receiver a second stopper.By acting out parts of the electrodes connect the wires.Attach the wires to the power supply near the electrode connected to the negative pole will appear red cloud.Remove the tube from the source and shake it - it will return to its original state.