Many objects around you contain electromagnets. They are found in electric motors and loudspeakers. Electric bells like the ones used in most schools also contain an electromagnet. The slideshow ...
Electromagnets have some advantages over permanent magnets. For example: they can be turned on and off the strength of the magnetic field can be varied These properties make electromagnets useful ...
一些您可能无法访问的结果已被隐去。
显示无法访问的结果