Phys_213_Midterm_2_-_Fall_2007

# Phys_213_Midterm_2_-_Fall_2007 - EXAM II Physics 213...

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Unformatted text preview: EXAM II : Physics 213 Chapters 1,3, and 4 October 24th 2007 The exam contains FIVE questions on EIGHT pages. Except for Question 1, you must show all work and give explanations. ****THE CORRECT ANSWER WITH NO EXPLANATIONS OR WORK SHOWN IS WORTH ZERO POINTS. **** Conversely, the WRONG answer with all work shown will be given partial credit IF the steps shown are logical. You may bring ONLY a calculator and pencil/pen. Nothing else. All answers reguire units and all vectors require direction. All formulae are on a separate sheet. Good luck! Question 1. /25 points Question 2. /45 points Question 3 /30 points Question 4 /30 points we Question 5 - /20 points TOTAL / 150 Useful constants h: 6.63 X 10‘34 Is: 4.14 X 10‘15eV.s c=3 X lOgm/s Elementary charge, e=1.6 X 10’19 C Mass of an electron 29.11 X 10'31 Kg Boltzmann Constant k=l.38 X 10'23J/K28.62 X 10'5 eV/K Stefan Boltzmann Constant 0:5.67 X 10”8 W/(m2K4) 80:8.85 X 10'12 F/m 1 eV=l.6 X 10'19 Joules Moz4n X 10'7 T.m/A Mass of hydrogen atom=1.6727 X 10'27 Kg NAME Q. 1. ( 25 pts) ‘ 1. ( 10 points) In the Bohr model of the hydrogen atom, which of the following quantities Wat offnche orbiting electron increase as 11 increases? ,. Total Energy “f; 3 M03? Potential energy "' fC]Spacing between consecutive energy levels [m Orbital radius /’ l3 :ESpacing between consecutive radii (“[F Angular momentum 2. ( 5 pts) In the two dimensional rectangular lattice indicated below, an x-ray beam of wavelength 1A is incident as shown. It is found that when 6 = 300, the x~ray beam intensity is high. What does that indicate regarding the spacing? x—ray beam .—___..___..____.___._____.__~_____ 0 [gr x=0.5 A Q] :1 ‘ (3 ﬂ; ‘1 x=2A “2“” K i [D] x=0.577A ; AR. [E] x=0.707A 3. ( 5 pts) An electron (negative q) goes through crossed E and B ﬁelds. The initial electron velocity is along the positive x—axis (horizontal). Which of the following E and B ﬁeld combinations will result in a possible zero deﬂection of the electron beam? (There may be more than one possibility) [A] E along +ve x—axis, B along +ve y axis [B] E along +ve y—axis, B along +ve x axis {g} E along +ve y-axis, B along +ve z axis”? {DIE along —ve y—axis, ’t B along +ve z axis along +ve y—axis, B along we 2 axis w‘along -ve y—axis, B along —ve z axis NAME 4. ( 5 pts) The work function of Pt is 6.35 eV and the work function of Na is 2.28 eV Na Stopping voltage Frequency of light The heavy black line labeled Na represents the photoemission of electrons from a clean Na surface. Which line best represents the photoemission from a clean Pt surface? (Note: lines 1 and 2 are parallel to the Na line. Lines 3 and 4 are parallel to each other but not to the Na line). [A] 1 (BE 2 [C] 3 [D] 4 [E] 5 NAMEW .2. ( 45 points) A hydro en atom is in a state having an ionization ener y of 0.85 eV. 8 g (i) ( 10 pts) What is thewgnantummnumiber of this state ? E X p a?“ :3. i 4 M_WWW .4; 3i W g i ? ._ :W K} \j z t k g ‘ S _ h ‘ A {k gf’z Frequency=g Wavelength: ['f'" E NAME (iii) ( 15 pts) Show the transition on an energy level diagram. Include all the energy levels upto and including that found in (i) as well as the vacuum level. ( r Vie i L H L we ( m ©th - mwmwwmuMWQMWWWWMWWWWNaa,»«warm,an“MN _ axmmmmm NAME f ﬂy { ‘ “ (2.3. ( 3O pts)£w}rat fraction of a beam of 7.7 MeV alpha particles incident upon a gold foil 3.0 X 10 ' m hick is scattered by angles > 90°? The area of the beam is lcmz. First calculate the impact parameter. Then calculate the fraction that will be scattered by angles greater than 90°. 4JL’80Eb 2 The Rutherford scattering formula: Cot(t9/ 2) = where Ze E: kinetic energy of the alpha particle, Z =atomic number of the foil b: impact parameter. Z of gold: 79 Nuclear density =5.902 X 1022 nucle “a r: ,; NAME Q.4.( 30 points) A black body has its maximum spectral radiance at a frequency of 0.1 X 1014 Hz (i) ( 15 pts) What the temperature of the black ‘ The temperature of the black body is now increased so that the total emission over the entire frequency range is doubled (ii) ( 15 pts) What is this new increased temperature? -- 4* ,,,,,,, M W it * a; K i ,, Wymwrwwmsﬂmy.immwwma , wr- » ~ ,’ NAME Q. 5. ( 20 points) Photons of wavelength 240 A are incident on a target containing free electrons. (i) ( 10 pts) Find the wavelength of a photon that is scattered by 30 0 from the incident direction. t g / xi (.2 EM} {75,13 Wavelength of scattered photon: (ii) ( 10 pts) What is the kinetic energy imparted to the recoil electron? ( Be careful about units) Kinetic energy = CD (“it ...
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## This note was uploaded on 04/18/2008 for the course PHYS 213 taught by Professor Adenwalla during the Fall '07 term at UNL.

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Phys_213_Midterm_2_-_Fall_2007 - EXAM II Physics 213...

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