PHYSICS 3204 PUBLIC EXAM QUESTIONS (Quantum pt.1)

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1 PHYSICS 3204 PUBLIC EXAM QUESTIONS (Quantum pt.1) NAME: August How much energy is carried by a photon having frequency 1.5 x10 Hz? (A) 1.4 x10 J (B) 9.9 x10 J (C) 3.0 x10 J (D) 1.3 x10 J 42. A metal has a work function of 4.50 ev. What is the maximum kinetic energy of the ejected electrons if the wavelength of the incident light is 2.50 x10 m? (A) 0.37 ev (B) 0.46 ev (C) 4.97 ev (D) 9.47 ev 43. A photon with energy Eo strikes a free electron. The photon is deflected in the opposite direction, with energy E. What is the resulting kinetic energy of the electron? (A) Eo (B) E (C) Eo - E (D) Eo + E What is the frequency of a photon of light that has a momentum of 2.80 x10 N s? (A) 2.37 x10 Hz (B) 4.21 x10 Hz (C) 4.23 x10 Hz (D) 1.27 x10 Hz 45. What is the mass of an object thrown with a speed of 45 m/s and having a de Broglie wavelength of x 10 m? (A) kg (B) kg (C) 22 kg (D) 88 kg 46. Which best explains why each atom in the periodic table has a unique set of spectral lines? (A) Each atom has a unique neutron to proton ratio. (B) Each atom has a unique set of energy levels. (C) The electrons in atoms are in constant motion. (D) The electrons in atoms orbit the nucleus. 3% 53.(a) The stopping potential of a metal is 2.4 V. Calculate the work function if light incident on the metal has a wavelength of 4.0 x10 m. 3% (b) A light source of wavelength illuminates a metal and ejects photoelectrons with a maximum kinetic energy of 1.00 ev. A second light source of wavelength ½ shines on the same metal and ejects photoelectrons with a maximum kinetic energy of 4.00 ev. Calculate the work function of the metal.

2 2% 53.(c) Use Bohr energy levels to explain fluorescence and phosphorescence. June Which phenomenon supports the particle theory of light? (A) diffraction (B) interference (C) photoelectric effect (D) refraction 42. What is the minimum energy that will allow electrons to be ejected from a metal surface during the photoelectric effect? (A) black-body radiation (B) Planck s constant (C) stopping potential (D) work function How much energy is possessed by a photon with a frequency of 1.00 x10 Hz? (A) 4.73 x10 J (B) 4.37 x10 J (C) 6.63 x10 J (D) 6.63 x10 J What wavelength of light has 4.70 x 10 J of energy? (A) m (B) m (C) 63.8 m (D) 422 m What is the speed of a 50.0 kg person having a de Broglie wavelength of 4.4 x10 m while running? (A) 1.3 x10 m/s (B) 3.3 x10 m/s (C) 3.0 x10 m/s (D) 7.5 x 10 m/s 46. The graph provided shows the maximum kinetic energy of ejected electrons plotted against the frequency of the light shone on four different metals, A, B, C and D. What is the unknown metal if light of wavelength 1.87 x10 m shines on it and the maximum kinetic energy of the ejected electrons is 2.5 ev? (A) A (B) B (C) C (D) D

3 47. What is true of the distance, r, between adjacent orbital radii in a H atom? 2 2 (A) r n (B) r n (C) r 1/n (D) r 1/n 15 3% 53.(a) When light having frequency 3.0 x10 Hz is shone on a certain metal, electrons are ejected. If the stopping potential of these electrons is 7.0 V, calculate the work function of this metal. 3% 53.(b) Two subatomic particles with very different masses have the same de Broglie wavelength. Explain how this is possible. 2% 53.(c) An electron in a hydrogen atom gains ev of energy as it jumps from one energy level to another. Calculate what energy level the electron moves to if it starts at energy level 3. August Which occurs when an opaque object with a temperature above absolute zero emits photons? (A) black-body radiation (B) Compton effect (C) photoelectric effect (D) UV catastrophe

4 What is the energy of a photon having a frequency of Hz? (A) J (B) J (C) J (D) J 43. The diagram below shows the bright line spectra of four elements along with the spectrum of an unknown gaseous sample. Which elements are found in the unknown sample? (A) A and C (B) A and D (C) B and C (D) B and D What is the stopping potential for an ejected photoelectron that has J of kinetic energy? (A) V (B) 2.13 V (C) 3.40 V (D) 5.44 V 45. What is the debroglie wavelength of a 125 g baseball moving at 28.0 m/s? (A) m (B) m (C) m (D) m 46. What is the momentum of a photon of yellow light with a wavelength of m? (A) kg m/s (B) kg m/s (C) kg m/s (D) kg m/s 47. What is the energy of an electron in the third energy level of a hydrogen atom? (A) 13.6 ev (B) 4.53 ev (C) 2.27 ev (D) 1.51 ev 2% 53.(a) The diagram below shows the first five energy levels of an electron orbiting the nucleus of a hydrogen atom. Calculate the wavelength of the emitted photon for the electron transition indicated by the arrow in the diagram.

5 3% 53.(b) The spectra of two light sources through spectroscopes are shown in the diagram below. i) What type of spectra is produced in each case? ii) Explain why the observed spectra are different. June What is represented by the ratio of the energy of a photon to its frequency? (A) photon speed (B) photon wavelength (C) Planck s constant (D) speed of light 42. Blue light is shone on a metal surface and electrons are ejected at a given rate and with a certain amount of energy. If the intensity of the blue light is increased, which describes the rate and the energy per electron of the ejected electrons? Rate Energy per Electron (A) decreases constant (B) increases constant (C) constant decreases (D) constant increases 43. What is the wavelength of a photon having an energy of 2.12 ev? (A) m (B) m (C) m (D) m 44. By what factor does the energy of a photon change if its wavelength is halved? (A) ¼ (B) ½ (C) 2 (D) What is the orbital radius of an electron in the third energy level of a hydrogen atom? (A) m (B) m (C) m (D) m

6 46. The diagram below shows spectral lines for hydrogen when viewed through a spectroscope. Which line corresponds to an electron transition from energy level 3 to energy level 2? (A) A (B) B (C) C (D) D 47. In case of a power failure, doors and stairways in large buildings are often outlined with special paint that glows for some time after the lights go out. What is illustrated in this situation? (A) black-body radiation (B) fluorescence (C) phosphorescence (D) photoelectric effect 3% 53.(a) Calculate the maximum wavelength that will cause photoelectric emission from a metal surface having a work function of 2.00 ev. 3% 53.(c) In a photoelectric effect experiment, light was shone on a metal surface and the data below were recorded. i) Graph these results, including the line of best fit. ii) Use the graph to determine the work function for this metal surface.