Experiment 29 and 30 require the TEA2025B audio amplifier from STMicroelectronics. This IC is very hard to acquire locally. I finally ordered 50! of them in China (Aliexpress.com) for a very low price (14 cents a piece). Until I receive them I continue with the other experiments.
Experiment 25 demonstrates magnetism as an induced effect of electrical current through a wire. A long piece of wire is winded around the shaft of a screwdriver. The ends of the wire are connected to an AA battery (see image below). Due to the induced magnetism a paperclip or some other lightweight iron is attracted to the screwdriver. Very neat. This experiment in one form or the other can be found numerous times on the web. A nice example is Colin Cunninghams YouTube movie on the subject at https://www.youtube.com/watch?v=STDlCdZnIsw.
|Experiment 25: Wire winded around the shaft of a screwdriver.|
|Tada, magnetism induced. I used eight feet of wire and a 9V block battery.|