Gun barrel and headphones: what they have in common

1. Step 1. Gun barrel — is part of — Anti-aircraft gun. A long barrel.
2. Step 2. Anti-aircraft gun — uses — Radar. Radar guidance.
3. Step 3. Radar — has part — Magnetron. The cavity magnetron made compact radar possible.
4. Step 4. Magnetron — has part — Permanent magnet. A magnet makes the electrons spiral.
5. Step 5. Permanent magnet — is part of — Headphones. A magnet moves the diaphragm.

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