Physics: Why Electromagnets Can Be Switched and Tuned

Electromagnets are magnets whose magnetic field is produced by an electric current, rather than by a permanently magnetised material. Because the field exists only while current flows, switching the current on or off switches the magnetism on or off — something a permanent magnet can never do. Their strength is also controllable: increasing the current, or the number of turns in the coil, strengthens the field, while decreasing it weakens the field. This controllability is what makes electromagnets so useful in real-world machinery such as scrap-yard cranes. A permanent magnet would grip a car indefinitely, with no way to release it at the chosen spot, and its fixed strength would suit only one load size. An electromagnet, by contrast, can be switched off to drop its load exactly where needed, and its current can be adjusted to lift heavier or lighter cars as required. These two linked ideas — on/off control and variable strength — are the key advantages explored in this topic.