Name______________________			April 23, 2008      	            mult choice____
          (Please Print)								
	       Spring 2008			prob       ____	
	University Physics III		
		Examination III		total     _______
 Multiple choice 4 pts each

__________1. In the Compton Effect, which of the following cases would a scattered photon show the greatest percentage change in wavelength? 
(a) a 1 eV photon scattering by 90 degrees off an electron
(b) a 1 eV photon scattering by 180 degrees off an electron
(c) a 1 MeV photon scattering by 90 degrees off an electron
(d) a 1 MeV photon scattering by 180 degrees off an electron
(e) same change in all cases

__________2. Two hydrogen atoms each with kinetic energy K collide head on, after which each has kinetic energy K/4.  Find K if the atoms are initially in their n=1 state before collision and their n=2 state afterwards. Hint: conserve total energy.
(a) 13.6 eV
(b) 27.2 eV
(c) 54.4 eV
(d)  6.8 eV
(e) none of the above

__________3. How much energy is required to ionize a He+ ion (atomic number 2) initially in its ground state?
(a) 13.6 eV
(b) 27.2 eV
(c) 54.4 eV
(d)  6.8 eV
(e) none of the above

__________4. Who discovered the atomic nucleus?
(a) Bohr
(b) Einstein
(c) Planck
(d) Rutherford
(e) none of the above

__________5. What is the deBroglie wavelength of a baseball of mass 0.2 kg moving at 10 m/s?
       (a) 3.3 x 10-32 m
       (b) 3.3 x 10-34 m
       (c) 3.3 x 10-36 m
       (d) 3.3 x 10-38 m
 (e) none of the above

__________6. A pair of electrons of mass m each moving at 98 percent the speed of light collide head on.  Following the collision the electrons disappear, and a pair of identical X particles are formed.  What can be said about the rest mass of either of the X particles?
(a) it equals 5m
(b) it equals 10m
(c) it is no more than 5m
(d) it is no more than 10m
(e) none of the above

___________7. A person in a rocket ship travelling past earth at 98 percent the speed of light observing clocks in her ship and clocks on earth finds
(a) her own clocks keeping normal time, and earth clocks running five times slower
(b) her own clocks keeping normal time, and earth clocks running five times faster
(c) her own clocks running five times slower, and earth clocks keeping normal time
(d) both sets of clocks running five times slower
(e) none of the above

___________8. Which of these observations about the photoelectric effect IS consistent with the wave model of light?
(a) a threshold (cutoff) frequency exists
(b) no dependence of stopping potential on light intensity
(c) no appreciable time delay before emission of electrons
(d) ejected electrons have a range of kinetic energies
(e) none of the above

____________9. Two rocket ships each travelling at half the speed of light approach each other head on.   What is the magnitude of the speed of Captain Kirk's ship according to Captain Picard?
(a) c
(b) 0.6c
(c) 0.7c
(d) 0.8c
(e) none of the above

____________10. What percentage error is made by using the non-relativistic expression for kinetic energy applied to an object moving at ten percent the speed of light?
(a) 1.3 percent
(b) 10 percent
(c) 0.76 percent
(d) 3.1 percent
(e) none of the above

____________11. An electron and a positron (an anti-electron) annihilate each other when they are at rest and produce two photons.  We know that they must produce two photons not one, because otherwise
(a) energy could not be conserved
(b) momentum could not be conserved
(c) the photon's energy would have to be infinite
(d) all the above
(e) none of the above

____________12. In the photoelectric effect, a metal A is exposed to photons of energy 2.0 eV, and the stopping potential for ejected electrons is found to be 1.0 eV.  When a second metal B is
exposed to the same 2.0 eV photons, the stopping potential is found to be 0.5 eV.  Which metal
has the higher cutoff frequency?
(a) A
(b) B
(c) no difference
(d) not enough information has been given to tell

Problem.

(a) What wavelength could barely be resolved from a spectral line at 500 nm in second order using a 50,000 slit diffraction grating?

(b) When light passes through a single slit and forms a diffraction pattern, it is found that the first secondary maximum (away from the central max) of one wavelength, λ1, occurs at the same angle as the first minimum of a second wavelength, λ2.  What is the ratio λ1/λ2?

(c) Consider two events A and B: A occurs right now on earth, and B occurs on a star 20 light years away and 10 years from now (according to earth observers).  Using the Lorentz Transformation, find the speed and direction of an observer for whom event A occurs simultaneous with event B.  Note, that the speed of light can be expressed as 1.0 light years per year.

(d) A Polaroid filter blocks half the light incident on it.  Was the incident light polarized or unpolarized?  No credit without proper explanation.

(e) Describe in clear English with the aid of a diagram the Michelson-Morley experiment.  Why was it done?  What did it find & what role did it play in the history of physics?