For this experience fit any aluminum spoon - tea or dining room. It must be thoroughly clean and degrease; how to do it, you know from the experiments with anodized aluminum. Spoon will be the first part of the future of the rectifier, and the second we will empty tin can, a height of about with a spoon, anyway, not much lower.
Tin can wash with soap or detergent, rinse and fill with a solution for anodizing aluminum: 100 ml water, 20 ml of sulfuric acid (caution!). Acid can be replaced by ammonium carbonate (NH4)2CO3 (10 g), or at least baking soda, dissolved it in water until saturation. The water should be distilled, good and clean rainwater.
Before you drop the spoon into the jar, estimate, to which place the spoons will come to a solution. At the boundary of the solution - air aluminum will intensively be dissolved, and the spoon will soon fall apart into two parts. To avoid this, the area near the border cover with a layer of varnish or waterproof glue.
Now hang the spoon in the pot so that it does not touch the walls; the suspension device you can probably easily think of. Under the Bank put tile or any other not conduct electricity stand. This time we will not use batteries or battery and alternating current from the mains, and, of course, need to protect yourself. For the same reason, carefully insulate all bare ends of the wires, and during the experience do not touch the spoon, nor to the Bank. It is best if before current is switched on you will cover them upside down plywood box or plastic bucket.
The electrical circuit is simple: plug it into the circuit in series with a light output of about 40-60 watts, a switch, a spoon and a jar; if you have an ammeter, you can connect it. When the circuit is collected and the reliability of the isolation checked, turn on the current.
First, as you can guess, the lamp lights up because the solution is in the Bank conductive. But after about half an hour she will Shine much weaker, and then goes off. Spoon became a rectifier. It passes current only in one direction - from banks to spoon.
This would be easy to verify if you have a oscilloscope on the screen at the beginning of the experience was shining would be a sine wave, and at the end of the lower branch would disappear: in the circuit flows so-called pulse current. The oscilloscope would at once set, where the positive pole of the rectifier, and where negative (this is very important if you are going to put improvised rectifier electrochemical experiments). But you can do without instruments: the polarity of the rectifier easily be installed using a strip of filter paper, moistened with a weak solution of common salt with the addition of phenolphthalein indicator.
Disconnect the power, press the sheet toward the spoon and the pot and secure it, such as a plastic linen clothespins. Turn on the current, and a few minutes later, the filter paper will depart from one of the poles. This pole is negative. In the electrolysis of water (salt need only to increase the conductivity) on the negative electrode (the cathode) is secreted hydrogen ions and ITis remain in excess. These ions cause alkaline properties, so the indicator paper red.
The same test damp indicator paper with salt and phenolphthalein you can spend and if you messed up the pole of the battery or batteries. As the voltage is low, a strip of paper, you can simply press a hand to both poles of the power source.
But why aluminum spoon became a rectifier? After turning the current on it, as and when anodizing aluminum, growing the oxide film of aluminum. And this film - semiconductor: passes current in only one direction. Her property is often used in the technique.
Using makeshift rectifier can put some electrochemical experiments, which are described in this book. But in accordance with the terms of expertise include the rectifier through a step-down transformer. The voltage in any case should not exceed 40 C. And the current, which can be removed from aluminum spoons, can reach several tens of amperes.
But do I have to take for rectifier spoon and a tin? Of course, no. Instead of a spoon, you can take the aluminum electrode of any shape, instead of banks - iron, lead or graphite electrode and immerse them in a glass vessel into which is poured the electrolyte solution. Moreover, we advise you to do if you decide to use homemade rectifier in practice. But if you are going to demonstrate how the aluminum oxide rectifies the alternating current, the spoon can look much more spectacular...