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Phys 116, Winter 2003
Non-Calculus Physics, 3rd Q

Exam 3 Solutions

Matching  (21 points):  If nothing seems to match, write in your own definition

Compton                     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

  1. (24 pts) A 220X astronomical telescope is adjust for a relaxed eye when the two lenses are 2.25 m apart.  Its diameter is 45 cm.  A) (10) What is the focal length of each lens? 

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.) X-ray 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 Balmer-like 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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