Which one of the following has the largest energy content ?
Correct answer: A. 103 photons of wavelength 2 pm (γ-rays)
- A. 103 photons of wavelength 2 pm (γ-rays)
- B. 102 photons of wavelength 1nm (x-rays)
- C. 106 photons of wavelength 50?m (infrared)
- D. 106 photons of wavelength 200nm (UV)
Explanation
Total energy is Nhc/λ. Taking hc = 1.986 x 10^-25 J m, option a gives (10^3)(1.986 x 10^-25 J m)/(2 x 10^-12 m) = 9.93 x 10^-11 J, which is greater than b = 1.986 x 10^-14 J, c = 3.972 x 10^-15 J, and d = 9.93 x 10^-13 J. The likely mistake is comparing wavelength alone and ignoring the different numbers of photons.
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The particle model treats light as photons with energy E equals hf and momentum related to wavelength. Questions involve the photoelectric effect, work function, threshold frequency, stopping potential and photon energy, while distinguishing particle behaviour from the wave description of interference and diffraction.
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