Photographic film and lead–acid battery: what they have in common

1. Step 1. Photographic film — is used in — Film projector. It shows film.
2. Step 2. Film projector — has part — Incandescent light bulb. The light source (formerly an arc).
3. Step 3. Incandescent light bulb — is part of — Torch (flashlight). A bulb (today an LED).
4. Step 4. Torch (flashlight) — has part — Dry cell. Batteries.
5. Step 5. Dry cell — evolved from — Voltaic pile. A convenient form of the galvanic cell.
6. Step 6. Voltaic pile — evolved into — Lead–acid battery. Planté’s battery developed the idea of a chemical current source by making it rechargeable.

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