Pantograph and modem: what they have in common

1. Step 1. Pantograph — is part of — Electric locomotive. Current is collected by a pantograph.
2. Step 2. Electric locomotive — has part — IGBT. Traction converters.
3. Step 3. IGBT — uses — P–n junction. A transistor structure with p–n junctions.
4. Step 4. P–n junction — is used in — Photodiode. Light generates a current in the p–n junction.
5. Step 5. Photodiode — is used in — Fax. Scanning with a photocell.
6. Step 6. Fax — has part — Modem. It transmits an image over a telephone line.

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