MIKKEL JUUL JENSEN / SCIENCE PHOTO LIBRARY MIKKEL JUUL JENSEN / SCIENCE PHOTO LIBRARY
Magnetic field of electromagnetic coil and core. Illustration of the magnetic field lines (black lines with arrows) for the magnetic field generated by an electrical wire (yellow) coiled around a block of a ferromagnetic metal such as iron. The direction of the current (white arrows) determines the direction of the magnetic field in both the wire (small circles) and the magnetic field (larger curved lines) that is induced in the metal when the electric current is switched on. Magnetic north is at left and magnetic south is at right. If the polarity of the current is reversed, the magnetic field direction also switches. The magnetic core concentrates the magnetic flux and makes a more powerful magnet. Such electromagnetic coils of wire have a range of applications and uses, from electromagnets to inductors, transformers and inducers.
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