the citadel or high fortified area of an ancient Greek city. the Acropolis, the citadel of Athens and the site of the Parthenon.
Electromagnets are used in a number of everyday devices. One useful characteristic of an electromagnet is the fact that you can vary its magnetic force by changing the amount and direction of the current going through the coils or windings around it.ummary. Electromagnets are used in a number of devices, such as loudspeakers and tape recorders. Some electromagnets can be very strong and its power can be readily turned off and on, such as in junk yard electromagnets and electromagnetic locks.
An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of soft ferromagnetic material such as steel, which greatly enhances the magnetic field produced by the coil. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces.