quiz2_key_f08 - Quiz 2a 2008 General Information E = h = c...

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Quiz 2a 2008 General Information: E = h  = c E K = h - E K = ( ½ )mv 2 h = 6.626 x 10 -34 Js c = 2.998 x 10 8 m/s mass of proton = 1.67 x 10 -27 kg; mass of electron = 9.11 x 10 -31 kg N A = 6.022 x 10 23 1 eV = 1.6022 x 10 -19 J 1 W = 1 J/s 1 J = 1 kg m 2 /s 2 1 nm = 10 -9 m 1 Å = 10 -10 m -------------------------------------------------------------------------------------------------------------------------------- 1. a) The work function for zinc is 4.31 eV. How many seconds must a 50 W bulb of 250 nm be turned on to eject 4.7x10 20 electrons from a zinc surface? Please circle your answer. J 10 x 95 . 7 m 10 nm 1 nm 250 ) s / m 10 x 998 . 2 )( Js 10 x 626 . 6 ( hc E 19 9 8 34 p For Zn: = 4.31 eV J 10 x 91 . 6 eV J 10 x 6022 . 1 19 19 Ep > electrons will be ejected (or could show max = 287 nm and so > max ) J 7 . 373 ) electrons 10 x 7 . 4 ( electron 1 photon 1 photon 1 J 10 x 95 . 7 20 19 sec 47 . 7 J 50 sec 1 J 7 . 373 b) If the zinc surface is illuminated with photons of 275 nm, what is the maximum velocity the ejected electrons will have? Please circle your answer. 2 K mv 2 1 hc E 2 31 2 2 19 9 8 34 v kg 10 x 11 . 9 2 1 J 1 s / m kg 1 J 10 x 91 . 6 m 1 nm 10 nm 275 ) s / m 10 x 998 . 2 )( Js 10 x 626 . 6 ( v 2 = 6.98 x 10 10 m 2 /s 2 v = 2.64 x 10 5 m/s 2. Sketch a graph of the photocurrent versus frequency for a cesium cathode ( Cs = 1.90 eV) in a photoelectric cell. Sketch the results obtained when the experiment is performed with two different light sources. The second light source (L 2 ) has a photon flux that is half the value of that of the first light source (L 1 ). Assume that a constant number of photons per second are emitted over the entire frequency range of the graph. Label the axes, and lines and any
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  • Spring '08
  • HOCKINGS
  • Electron, Proton, 5.5 seconds, 10 photons, 10 14 sec, 20 1 photon, 21 photons

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