Suitable for use in electromagnetic or induction experiments of solenoid coils. Can be tested with transformer and iron filings. Liquid-coated copper coil Diameter 1 mm. threaded solenoid. The diameter of the thread is about 3 cm, not less than 15 turns, put in a transparent plastic rod of not less than 8x10 cm. It is convenient to observe the arrangement of the iron filings and place the compass.