Lead dioxide plates and telephone: what they have in common

1. Step 1. Lead dioxide plates — is part of — Lead–acid battery. Positive electrodes.
2. Step 2. Lead–acid battery — uses — Electrochemical reaction. A reversible reaction of lead and lead dioxide in sulfuric acid.
3. Step 3. Electrochemical reaction — is used in — Fax. The paper darkened under current.
4. Step 4. Fax — uses — Telephone. Transmission over a telephone line.

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