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1 Mid-Term Exam 2 Physics 23 Modern Physics Tuesday October 23, 2 Point distribution: All questions are worth points 5 points. Questions # - #6 are multiple choice and answers should be bubbled onto the answer sheet. Questions #7 - #2 are long-answer questions, and partial credit will be given. Alot your time accordingly. Constants and Conversion Formulas Speed of light c =3: 8 m/s Coulomb's Force Constant k =8:99 9 Nm 2 /C 2 Rydberg Constant R =:,2 nm, Rydberg Energy E R = hcr =3:6 ev Bohr Radius a B =h 2 =(ke 2 m e )=5:29,2 nm Stefan Constant =5:673,8 W/m 2 K 4 Planck's Constant: h =4:44,5 ev s = 6.63,34 Js h = h=(2) =6:58,6 ev s =.5,34 Js hc = 24 ev nm = 24 MeV fm hc = 97 ev nm = 97 MeV fm MeV/c 2 =:78,3 kg MeV/c = 5.34,22 kg m/s e =:6,9 C Mass conversion Momentum conversion Elementary Charge Mass of Electron m e =:5 MeV/c 2 Mass of Proton m p =938MeV/c 2 Electron Volt ev =.6,9 J Spectroscopic Series Lyman (n! ), Balmer (n! 2), Paschen (n! 3). Which of the following experiments involved light shined onto to an electrode to generate electrons? a. Blackbody radiation. b. Bragg diraction. c. Photoelectric eect. d. Compton eect. 2. Which of the following experiments did NOT yield a measurement of Planck's constant, h? a. Blackbody radiation. b. Photoelectric eect. c. Duane-Hunt experiment. d. Davisson-Germer experiment. 3. Which experiment is credited with establishing that light carries momentum? a. Compton eect. b. Blackbody radiation c. Photoelectric eect. d. Millikan's oil drop experiment.

2 4. Which of the following experiments provided the FIRST evidence for the quantization of energy? a. Blackbody radiation. b. Photoelectric eect. c. Duane-Hunt experiment. d. Davisson-Germer experiment. 5. Which of the following was a fundamental problem of the Thompson model of the atom? a. Electron orbits were unstable. b. The atom was too large. c. The atom was too small. d. The distribution of charge was wrong. 6. Which of the following was a fundamental problem of the Rutherford model of the atom? a. Electron orbits were unstable. b. The atom was too large. c. The atom was too small. d. The distribution of charge was wrong. 7. Which of the following graphs most accurately represents the spectrum of blackbody radiation? (a) (b) 45 K 65 K 25 K 45 K 25 K 65 K (c) (d) 25 K 65 K 45 K 65 K 45 K 25 K 2

3 8. What's the frequency of a photon with a wavelength of 55 nm? a Hz b Hz c Hz d rad/s 9. What's the energy of a photon with a wavelength of 55 nm? a. 2.4 ev b. 3.6 ev c.. ev d.. ev. An electron has a kinetic energy of 3 ev. What's its wavelength? a. 43 fm b. 52 fm c. 76 fm d..72 nm. An electron has a kinetic energy of 2 MeV. What's its wavelength? a. 95 fm b. 38 fm c. 54 fm d. 756 fm 2. Which of the following formulas describes the shortest wavelength in the Balmer series? a. 4hc=E R b. 4hc=3E R c. 3hc=4E R d. 3hc=E R 3. Which of the following formulas describes the longest wavelength in the Balmer series? a. 5hc=E R b. 5hc=4E R c. 36hc=5E R d. 36hc=E R 4. Using the Bohr model of the hydrogen atom, what's the diameter of the orbit of the electron with n =? a nm b..6 m c..53 nm d..53 nm 3

4 5. The \work function" of Cesium is.9 ev. What's the maximum wavelength of light that can eject an electron from Cesium? a. 24 nm b. 652 nm c. 347 nm d. 86 nm 6. The speed of an electron is observed to be m/s with an uncertainty v =:%. Approximately what is the fundamental uncertainty in its position measured simultaneously with its speed? a. 3mm b. 6 m c..5 mm d. 6 m 4

5 Name: Mid-Term Exam 2 Physics 23 Modern Physics Tuesday October 23, 2 Problems 7-2 concern a E =MeV photon that collides with a free electron and scatters through 9. Show all your work neatly in order to receive full credit. Please place the nal answer in each box provided. 7. What is the wavelength of the incident photon?call it and present your answer in fm. 8. What is the wavelength of the scattered photon? Call it and present your answer in fm. 5

6 Name: 9. What is the energy of the scattered photon? Call it E and present your answer in MeV. 2. What is the kinetic energy of the recoiled electron. Call it K e and present your answer in MeV. 6

Chapter 27 Early Quantum Theory and Models of the Atom Discovery and Properties of the electron

Chapter 27 Early Quantum Theory and Models of the Atom 27-1 Discovery and Properties of the electron Measure charge to mass ratio e/m (J. J. Thomson, 1897) When apply magnetic field only, the rays are