A " portative electromagnet " is one designed to just hold material in place; an example is a lifting magnet.
2.
To achieve this, in applications like lifting magnets ( see photo above ) and loudspeakers a flat cylindrical design is often used.
3.
:: : : Permanent magnet ( I assume the OP is not talking about electromagnets ) lifting magnets usually have a mechanism for releasing the load when required.
4.
In many practical applications of electromagnets, such as motors, generators, transformers, lifting magnets, and loudspeakers, the iron core is in the form of a loop or magnetic circuit, possibly broken by a few narrow air gaps.
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