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A permanent magnet`s magnetic properties exist when the magnet is (magnetized). An electromagnetic magnet only displays magnetic properties when an electric current is applied to it. That is how you can differentiate between the two. The magnets that you have affixed to your refrigerator are Permanent Magnets, while electromagnets are the principle behind AC motors.
Permanent Magnet v. Electromagnet: Magnetic Strength
Permanent magnet strength depends upon the material used in its creation. The strength of an electromagnet can be adjusted by the amount of electric current allowed to flow into it. As a result, the same electromagnet can be adjusted for different strength levels.
Permanent Magnet v. Electromagnet: Loss of Magnetic Properties
If a permanent magnet loses its magnetic properties, as it does by heating to a (maximum) temperature, it will be rendered useless and its magnetic properties can be only recovered by re-magnetizing. Contrarily, an electromagnet loses its magnetic power every time an electric current is removed and becomes magnetic once again when the electric field is introduced.
Permanent Magnet v. Electromagnet: Advantages
The main advantage of a permanent magnet over an electromagnet is that a permanent magnet does not require a continuous supply of electrical energy to maintain its magnetic field. However, an electromagnet`s magnetic field can be rapidly manipulated over a wide range by controlling the amount of electric current supplied to the electromagnet.
A permanent magnet retains its magnetic properties for a long time.
A lodestone is a naturally occurring permanent magnet composed of magnetite, an iron-bearing mineral. Such magnets have been known since ancient times. Virtually all magnets used commercially today are made from synthetic magnetic materials. The most common such materials are alnicos-iron alloys containing aluminum, nickel, and cobalt. Magnetic materials containing such rare-earth elements as samarium or neodymium form very strong permanent magnets. Ferrites, which consist of ferric oxide (an oxide of iron) combined with the oxides of one or more other metals, are widely used in electronic devices. Flexible magnets are made by combining magnetic materials with plastics.
Permanent magnets are typically made into U-shaped horseshoe magnets, with the poles side by side; and bar magnets, with the poles at opposite ends.
Note: This is a high level overview of permanent magnets as they compare to electromagnets. There are more details available relating to the differences stated. Please contact us with your specific questions and we`ll be happy to share all the fine points.