8. A hydrogen atom is moving at a speed of 75.0 m/s. It absorbs a photon of wavelength 121 nm that is moving in the oppo

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8 A Hydrogen Atom Is Moving At A Speed Of 75 0 M S It Absorbs A Photon Of Wavelength 121 Nm That Is Moving In The Oppo 1 (769.53 KiB) Viewed 35 times

8. A hydrogen atom is moving at a speed of 75.0 m/s. It absorbs a photon of wavelength 121 nm that is moving in the opposite direction. By how much does the speed of the atom change as a result of absorbing the photon? 9. Suppose an atom of iron at rest emits an X-ray photon of energy 8.2 kV. Calculate the "recoil" momentum and kinetic energy of the atom Hint: do you expect to need classical or relativistic kinetic energy for the atom? Is the kinetic energy likely to be much smaller than the atom's rest energy? 10. Time delay in the photoelectric effect. A beam of ultraviolet light of intensity 1.6 x 10-12 Wis suddenly turned on and falls on a metal surface, ejecting electrons through the photoelectric effect. The beam has a cross-sectional area of lem?, and the wavelength corresponds to a photon energy of 10 eV. The work function of the metal is 5eV. How soon might one expect photoelectric emission to occur? Note: 1eV -1.6 x 10-19. (a) One classical model suggests an estimate based on the time needed for the work function en ergy (5 V) to be accumulated over the area of one atom (radius - 0.1 mm). Calculate how long this would be assuming the energy of the light beam to be uniformly distributed over its cross section (b) Actually, as Lord Rayleigh showed in 1916, the estimate from (a) is too pessimistic. An atom can present an effective area of about to light of wavelength corresponding to its resonance frequency Calculate a time delay on this basis (e) On the quantum picture of the proces, it is possible for photoelectron emission to begin immediately as soon as the first photon strikes the emitting surface. But to obtain a time that may be compared to the classical estimates, calculate the average time interval between arrival of successive 10 eV photons. This would also be the average time delay between switching on the source and getting the first photoelectron. Hint: think of the power as photons per unit time.