Practice Quiz Photons, Electrons and Atoms Name_______________________________ 1) What is the number of photons per second given off by a light bulb with a power of 100 Watts operating at an efficiency of 4.80%? Assume the wavelength of light to be 600 nm. A) 6.34 × 1018 photons/s B) 3.11 × 1018 photons/s C) 25.3 × 1018 photons/s D) 14.5 × 1018 photons/s Answer: D 2) Which one of the following is the correct expression for the energy of the photon? A) E = h/f B) E = hλ/c C) E = hc/λ D) E = hλ Answer: C 3) Which one of the following is correct for the energy of a 620 nm beam of light? A) 1.60 × 10-19 eV B) 2.10 × 10-19 J C) 3.21 × 10-19 J D) 1.60 × 10-18 eV Answer: C 4) The work function of a certain metal is 1.90 eV. What is the longest wavelength of light that can cause photoelectron emission from this metal? A) 231 nm B) 14.0 nm C) 344 nm D) 653 nm Answer: D 5) If the frequency of a photon is halved, what happens to its energy? A) It is doubled. B) It is halved. C) It is tripled. D) It is quadrupled. Answer: B 6) Light with a wavelength of 310 nm is incident on a metal that has a work function of 3.8 eV. What is the maximum kinetic energy that a photoelectron ejected in this process can have? A) 0.62 × 10-19 J B) 0.21 × 10-19 J C) 0.48 × 10-19 J D) 0.33 × 10-19 J Answer: D 7) Which one of the following is the correct expression of the cutoff frequency of the metal in terms of its work function? A) fO = WO/h B) fO = WO/c C) fO = h/WO D) None of the other choices is correct answer. Answer: A8) A beam of light with a frequency range of 3.01 × 1014 Hz - 6.10 × 1014 Hz is incident on a metal surface. If the work function of the metal surface is 2.20 eV, what is the maximum kinetic energy of photoelectrons ejected from this surface? A) 0.32 eV B) 0.21 eV C) 0.42 eV D) 0.16 eV Answer: A 9) The frequency of a light beam is doubled. Which one of the following is correct for the momentum of the photons in that beam of light? A) It stays the same. B) It is halved. C) It is doubled. D) It is quadrupled. Answer: C 10) What is the momentum of a photon of light that has a frequency of 3.7 × 1014 Hz? A) 1.5 × 10-28 kgΧm/s B) 2.1 × 10-28 kgΧm/s C) 4.4 × 10-28 kgΧm/s D) 8.2 × 10-28 kgΧm/s Answer: D 11) A certain photon after being scattered from a free electron at rest moves at an angle of 120° with respect to the incident direction. If the wavelength of the incident photon is 0.611 nm, what is the energy of the scattered photon? A) 1.05 × 10-16 J B) 2.10 × 10-16 J C) 5.71 × 10-16 J D) 3.23 × 10-16 J Answer: D 12) A beam of X-rays at a certain wavelength are scattered from a free electron at rest and the scattered beam is observed at 51.0° to the incident beam. What is the Compton shift? A) 2.76 × 10-13 m B) 0 m C) 3.56 × 10-13 m D) 8.99 × 10-13 m Answer: D 13) If the momentum of an electron is 1.95 × 10-27 kgΧm/s, what is its de Broglie wavelength? A) 340 nm B) 210 nm C) 170 nm D) 520 nm Answer: A 14) Which of the following is the correct equation for the momentum of a photon? A) p = (hc)/λ B) p = λ/c C) p = (hc)/f D) p = (hf)/c Answer:
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