The human eye can barely detect yellow light (6000 Å) that delivers 1.7 × 10⁻¹⁸ watt to the retina. Nearly how many photons per second does the retina receive?
Correct answer: D. More than 5 million
- A. 50
- B. 5
- C. 500
- D. More than 5 million
Explanation
Energy of one photon at 6000 Å =3.3 ✕ 10^(-19)J.power delivered =1.7 ✕10^ (-18) J/s, so photon per second =1.7✕ 10^(-18) /1.3 ✕ 10^(-19)=5 Thus, the retina receives about 5 photons per second .
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Classical physics cannot explain blackbody radiation and related observations, leading to Planck’s quantum theory, in which energy is emitted or absorbed in discrete packets. Photons provide the particle model of light, with energy and momentum linked to frequency and wavelength, including the photoelectric effect and its threshold frequency.
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