[saspinski (OP)]

A school is running out of business near my home. They are selling a lot of stuff, among them this electronic devices with 2 coils and 3 terminals (photo in annex) that I got.
I measured in one of them 150 Ohms between the extreme terminals and 75 Ohms between the middle one and the others. It is written 2x1800 0.3A. For the other one the figures were 14500 and 7250 Ohms. And it is written 2x18000 0.03A.
Moving a magnet through the squared hole it is possible to measure a voltage between terminals, but I suppose they were no designed only to show that to the students.

[Bored chemist]

They are the sorts of coils they use in school physics labs.
https://www.3bscientific.co.uk/demountable-transformer-d,pg_1000.html

[saspinski (OP)]

Thank you.
The squared hole is to insert an iron core. And the coils can be used as primary or secundary of a transformer.