P–n junction and greenhouse: what they have in common

1. Step 1. P–n junction — is used in — Photodiode. Light generates a current in the p–n junction.
2. Step 2. Photodiode — is part of — Pulse oximeter. A photodiode.
3. Step 3. Pulse oximeter — uses — Infrared radiation. Infrared absorption by haemoglobin.
4. Step 4. Infrared radiation — is used in — Greenhouse effect. Infrared radiation is trapped.
5. Step 5. Greenhouse effect — is used in — Greenhouse. Glass lets light in and holds heat.

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