Transcription: The theory of electromagnetism holds that changes in an electric field produce a magnetic field, which in turn will form a second electric field and so on. When a copper wire is wound around soft metal, such as iron, the magnetic force of the concentrated wire, or solenoid, will magnetize the metal, creating a powerful magnetic field. The electromagnetic current can be switched on and off. For example, when an electric current flows through the thick power cable of a metal trash crane, a powerful magnetic field is created in its electromagnet, which is then able to lift heavy pieces of iron an ...
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