How does a metal detector find a coin?
a coil makes a changing magnetic field, metal answers with eddy currents that a second coil picks up.
How does a metal detector find a coin buried in the ground? 🪙🔍
1️⃣ THE SENDER COIL: the round head has a coil of wire carrying alternating current. That makes a magnetic field that reaches into the ground — and flips direction thousands of times a second.
2️⃣ INSIDE THE METAL: a changing magnetic field makes currents swirl inside any metal (they're called eddy currents). Those swirling currents make a small magnetic field of their own.
3️⃣ THE LISTENER COIL: a second coil in the head feels that "echo" — and the detector beeps! Wood, plastic, glass and rock don't conduct, so they send no echo.
Airport walk-through gates use the same idea.
Field out, echo back!
Read the voiceover (transcript)
- How does a metal detector find a coin?
- A coil sends a magnetic field into the ground. It flips thousands of times a second.
- Metal in that field gets swirling currents. They make a magnetic field of their own!
- A second coil feels that echo, and it beeps! Wood and plastic send no echo.
- Field out, echo back!
- Next: why transformers hum! Follow for more!
Related lessons
Get new lessons + early access to the full course
One email when new lessons drop. No spam, unsubscribe any time.
✓ You're on the list! We'll email you when new lessons drop.
By joining you agree to the privacy policy.