At connection of measuring devices, it is important to observe polarity too. As a rule, on a current source the positive pole is designated by a badge ""+", and negative - a badge "" -"". If they are not put, it can be done in other ways.
It is required to you
- - solution of table salt and saltpeter;
- - potato;
- - candle;
- - reactants for the indicator.
Instruction
1. Attentively examine the case of a source of current. Near a clip of positive contact it has to be put ""+", negative - "" -"". In case the sign costs near one clip of a source, consider the second with the opposite sign.
2. If on a source of current there are no signs, attach to it two copper wires. During the work surely work only with the insulated surfaces to avoid electric shock. In a glass of warm water dissolve a tablespoon of table salt (sodium chloride). Lower in it wires. From the conductor connected to a negative pole vials of gas will begin to rise.
3. The same wires thrust at distance about 1.5 cm from each other in a half of crude svezherazrezanny potato. Leave a design energized within 10 minutes. Around the positive electrode (connected to a positive pole) potato will begin to become blue. This way suits for determination of polarity of sources up to 60 V.
4. Heat two conductors connected to a current source on the tribe of a candle. Soot will accumulate on a wire from a negative pole.
5. To make the indicator for determination of polarity of a source of current, take the glass call with a diameter of 10-15 mm, two stoppers and electrodes from the burned-down glow lamp. Insert electrodes into traffic jams so that they left from two parties. Cork a tube on the one hand with an electrode. Fill in such structure there: 1 parts of saltpeter, 4 parts of water, then dissolve 0.1 part of phenolphthalein in 1 part of wine alcohol and add 5 parts of glycerin.
6. Mix all this. Cork a tube of the second. Attach wires to the coming-out parts of electrodes. Attach wires to a current source, near the electrode attached to a negative pole the red cloudlet will appear. Disconnect a tube from a source and stir up it - it will return to an initial state again.