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quiz2-su

# quiz2-su - Physics 2D Quiz#2 Department of Physics UCSD...

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Unformatted text preview: Physics 2D Quiz #2 Department of Physics, UCSD Summer Session II — 2009 Prof. Pathria 14 August 2009 Some Useful Data Speed of light: c = 3x108 m/s. c = Af Plank’s constant: h = 6.626x1034 J .s Atomic mass unit (amu): 1 amu = 1.66054x10—27 kg = 931.5 MeV/c2 Rest mass of an electron: me = 9.11x10‘31 kg = 0.511 MeV/c2 1eV = 1.602x10-19 J Total energy of a particle: E = K + mac2 2 ymocz where 'y = (1 — 50—1/2 Energy-momentum relation for a particle: E2 = (pa)2 + (mocz)2 Energy—momentum relation for a photon: E = pc which implies that p = h f / c = h/A Photo—electric equation: eVs = hf — <15 2 h( f — f0) Compton scattering formula: X — A0 = m}: c(1 — 0030) Compton wavelength for an electron: mic = 0.00243 nm Instructions Please write your answers in your blue book, and make sure your secret code number is written on all pages in indelible ink. 1. An unstable particle with rest mass M is initially at rest. The particle spontaneously decays into two fragments that ﬂy off with velocities 0.60 and —0.8c. Making use of the conservation laws for both energy and momentum, determine the rest masses of the two fragments (in terms of M). 2. A neutron (of mass 1.008665 amu) is absorbed by the nucleus of a ura— nium atom (of atomic mass 235.04392 amu). The excited uranium nucleus then undergoes ﬁssion, creating a barium atom (of atomic mass 140.9139 amu), a krypton atom (of atomic mass 91.8973 amu), and three neutrons. Calculate the amount of energy released in this process. Express your answer in MeV. 3. In a photoelectric experiment, in which monochromatic light and a sodium photocathode are used, we ﬁnd a stopping potential of 1.85 V for A = 300 nm and 0.82 V for /\ = 400 nm. From these data, determine (a) a value for Planck’s constant h, (b) the work function 45 of sodium in eV (c) the threshold wavelength A0 for sodium. 4. In a Compton scattering experiment, the scattered photon has an energy of 150 keV while the recoiling electron (which was originally at rest) has a kinetic energy of 50 keV. (a) Determine the wavelengths, A and X, or the incident and scattered pho— tons. (b) Calculate the angle 0 at which the photon is scattered AND the angle (,0 at which the electron recoils. ...
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quiz2-su - Physics 2D Quiz#2 Department of Physics UCSD...

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