Phys 116, Winter 2003 

Exam 3 Solutions Matching (21 points): If nothing seems to match, write in your own definitionCompton a. matter waves De Broglie b. amplitude of matter waves Bohr c. λ distribution due to temperature
photoelectric .... d. indeterminancy principle Wien e. natural frequency Heisenberg f. hydrogen spectrum Ψ . . . . . . . . . . g. light produces electricity h. photon deflection by an electron i. orbiting electron atom model
B) (7) How far apart must two stars be apart in order to be resolved from one another if they are 12.2 light years from Earth? Use λ=520 nm. C) (7) How far away does the image appear to be when one is looking through the telescope? 3. (10 pts) _____ The Bohr atom model cannot explain which of the following . Include all that apply. (a.) Angular momentum of the electron when n= 2 or more, (b.) Spectrum of helium (c.) Xray generation, (d.) Energy of the electronic transition, (e.) Relative brightness of spectral lines, (f.) Average radius of the electron “orbit”, . (g.) electron distribution. 4. ( 10 pts)Radiation of a certain wavelength (the one you must find) causes electrons with a maximum kinetic energy of 0.68 eV to be ejected from a metal whose work function is 2.75 eV. ( a) (5) what is the wavelength of light? (b) (5) What will be the maximum kinetic energy (in eV) with which this same radiation ejects electrons from another metal whose work function is 2.17 eV? Number 5. (15 pts) The distance between lenses in a microscope is 18 cm. The focal length of the objective is 1.5 cm. If the microscope is to provide an angular magnification of –83 when used by a person with a normal nearpoint of 25 cm, what must be the focal length of the eyepiece? 6.(20 pts) (a) The first four energy levels above the ground state of a particular ionized atom with one electron are 40.8 eV, 48.4 eV, 51.0 eV, and 52.2 eV. (a) (5) What emission lines would you expect to see in a Balmerlike series in a spectrum of this atom? (b) (5) Would you be able to see any color from the lines in part a if you put this gas in a tube and ran a high voltage through it? Show all your work or reason to get full credit. (c ) (4) Would any of the transition lines be visible (400 to 700 nm) and which transitions would they be? Show work for full credit. (d ) (6) Which element is this and what is the average radius of the electron in the ground state? Show work for full credit. Extra Credit (5 pts or substitute for 3, 4 or 6:parts c and d) A free neutron (m = 1.67 x 10^{27} kg) has a mean life of 900 seconds. What is the uncertainty in its mass?


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