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If the rhodopsin molecules in each of 10 rod cells absorbs one photon of light at about the same time, a perceptible flash is sensed by the brain. This is the lowest level of light that produces a detectable signal in the mammalian visual system. Assuming that the light is green (say, 500 nm), how much energy is imparted to the system by the absorption of the ten photons? How does this energy compare to the energy required to lift a 1 Kg mass 1 meter against gravity? [The energy required to lift the mass is equal to the work done. Work and energy have the same units, Joules (1 Joule = 1 Kg m2/s2). The work done is equal to force times distance, and the force required is equal to mass times acceleration of gravity (g ≈ 10 m/s2).]
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