Rotating aluminium disc and modem: what they have in common

1. Step 1. Rotating aluminium disc — is part of — Electricity meter. It is turned by eddy currents.
2. Step 2. Electricity meter — has part — Permanent magnet. A braking magnet.
3. Step 3. Permanent magnet — is part of — Loudspeaker. A permanent magnet.
4. Step 4. Loudspeaker — is part of — Telephone. The earpiece reproduces the other person’s voice.
5. Step 5. Telephone — is used in — Modem. It works over a telephone line.

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