Permanent wave and transformer: what they have in common

1. Step 1. Permanent wave — uses — Heating element. Nessler's first machines heated the wound strands with electric heaters.
2. Step 2. Heating element — works like — Incandescent light bulb. A lamp and a heater use the same effect — a conductor heated by current; they differ in purpose, light or heat.
3. Step 3. Incandescent light bulb — evolved into — LED lamp. It replaced incandescent bulbs.
4. Step 4. LED lamp — has part — Rectifier. The driver in the base rectifies mains current and limits the LED current; in an ordinary bulb it has no transformer.
5. Step 5. Rectifier — is part of — Power supply. A rectifier.
6. Step 6. Power supply — has part — Transformer. A transformer.

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