Why does…? #7: Why do transformers hum?
the iron core changes size slightly 100 times a second on 50 Hz mains (magnetostriction) → a 100 Hz hum.
Ever stood near a transformer and heard that HMMMM? 🔊 Here's why 👇
1️⃣ IT'S A MAGNET: inside is an iron core. AC in the coil turns it into a magnet — and flips it again and again (50 Hz in India, UK, Europe · 60 Hz in the USA, Canada).
2️⃣ THE IRON STRETCHES: every time the iron is magnetised it gets a tiny bit longer, then shrinks back. It's called magnetostriction — only a few millionths of its length, but enough to shake the air.
3️⃣ TWICE PER CYCLE: north or south, the iron stretches either way — so it stretches twice per AC cycle. 50 Hz mains → a 100 Hz hum (120 Hz in the USA). That's the sound you hear! 🎵
Magnet, stretch, hum!
Read the voiceover (transcript)
- Why do transformers hum?
- Inside is an iron core. AC turns it into a magnet, again and again.
- Every time it's magnetised, the iron stretches a tiny bit, then shrinks back!
- North or south, it stretches both ways. So fifty hertz makes a one hundred hertz hum!
- Magnet, stretch, hum!
- Next: why power lines need high voltage! Follow!
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