The key differences between a permanent magnet and an electromagnet are as follows:
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Magnetism:
- Permanent Magnet: A permanent magnet produces a persistent magnetic field due to the alignment of magnetic domains within the material. This magnetic field is always "on" and does not require an external power source.
- Electromagnet: An electromagnet generates a magnetic field only when an electric current flows through it. The strength of the electromagnetic field can be controlled by adjusting the amount of current.
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Control:
- Permanent Magnet: Permanent magnets cannot be turned off or on. Their magnetism is inherent and remains unchanged unless subjected to extreme heat or external magnetic fields that can demagnetize them.
- Electromagnet: Electromagnets can be turned off by stopping the electric current; therefore, their magnetism can be controlled.
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Applications:
- Permanent Magnet: Commonly found in everyday items like refrigerator magnets, speakers, and in motors where a constant magnetic field is needed.
- Electromagnet: Used in applications where variable or controllable magnetism is required, such as in electric bells, magnetic locks, and various types of machinery.
In summary, the statement "Electromagnets can be turned off and on; permanent magnets cannot" is correct, while the statement "Permanent magnets can be turned off and on; electromagnets cannot" is incorrect.