HC Verma: Concepts of Physics - Volume 2 Photoelectric Effect and Wave-Particle Duality Page 363: Q9 Solution: It is found that photosynthesis starts in certain plants when…

QPage 363: Q9: HC Verma: Concepts of Physics - Volume 2 Photoelectric Effect and Wave-Particle Duality Page 363: Q9 Solution: It is found that photosynthesis starts in certain plants when…

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Students often think that a high intensity of infrared light can drive photosynthesis, overlooking that each photon must have energy $E=hf$ above a specific threshold; intensity cannot compensate for photons whose wavelength is too long.

It is found that photosynthesis starts in certain plants when exposed to sunlight, but it does not start if the plants are exposed only to infrared light. Explain.

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**Answer:** Photosynthesis requires a minimum energy (threshold) to initiate the chemical reaction. Infrared light has lower energy photons than visible light, so it cannot provide the required activation energy. **Step-by-Step Explanation:** Photosynthesis is a photochemical process that requires photons of sufficient energy to drive the chemical reactions. Infrared photons have energy less than the threshold required, even though the total intensity (number of photons) might be high. Hence, photosynthesis does not start under infrared light.

QPage 363: Q9: HC Verma: Concepts of Physics - Volume 2 Photoelectric Effect and Wave-Particle Duality Page 363: Q9 Solution: It is found that photosynthesis starts in certain plants when…

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