An electromagnet is a piece of metal, usually with wire wrapped around it, that acts like a magnet only while electricity is flowing through the wire.

An electromagnet電磁鐵 is a piece of metal是一塊金屬 usually with wire wrapped around it通常外面纏著電線 only while electricity is flowing through the wire只在電線裡有電流通過的時候 that acts like a magnet才像磁鐵一樣

Switch the current on, and it can pull iron or steel; switch it off, and the pull stops. That on-and-off trick is the whole point: cranes in scrapyards, doorbells, and many electric motors use it.

Switch the current on把電流打開 it can pull iron or steel就能吸鐵或鋼 switch it off把電流關掉 the pull stops吸力就停了 That on-and-off trick這個開關的把戲 is the whole point就是重點 cranes in scrapyards廢車場的吊車 doorbells門鈴 and many electric motors use it還有很多電動馬達都用到它

A fridge magnet stays magnetic by itself; this one does not. It is a school-science and engineering word, but the object itself is ordinary once you know the name.

A fridge magnet冰箱磁鐵 stays magnetic by itself自己就能一直有磁性 this one does not這個不會 It is a school-science and engineering word它是學校科學和工程的用詞 but the object itself is ordinary但這東西本身很平常 once you know the name一旦你知道名字

Though actually, a little magnetism can linger after you cut the power, especially in some metals, but the working idea is still “magnetic when the current is on.”

Though actually不過其實 a little magnetism can linger還是會留一點磁性 after you cut the power在你切斷電源之後 especially in some metals尤其是某些金屬 but the working idea is still但基本概念還是 "magnetic when the current is on"「電流通的時候才有磁性」