Velocity of Electron ionized from Hydrogen

  1. 1. The problem statement, all variables and given/known data
    Ultraviolet light with a wavelength of 45.0nm shines on a gas of hydrogen atoms in their ground states. Some of the atoms are ionized by the light. What is the kinetic energy of the electrons that are freed in this process?
    I found the kinetic energy right but for some reason I thought I was looking velocity and when I solve for velocity I get a number much larger then the speed of light

    2. Relevant equations
    k=.5mv2
    k=14eV
    m=9.11*10-31kg

    3. The attempt at a solution
    k=.5mv2
    v2=2k/m
    v=√(2*14/9.11*10-31)=5.54*1015m/s
    am I doing something wrong or is there some quantum equation needed
     
  2. jcsd
  3. ehild

    ehild 11,786
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    Find the kinetic energy in joules, and calculate the speed with that value. Now you have the speed in units of eV0.5kg-0.5 instead of m/s.

    ehild
     
  4. Oh, thanks, I keep forgetting about that. I really need to start writing down the units
     
  5. ehild

    ehild 11,786
    Homework Helper
    Gold Member
    2014 Award

    It is a good idea !:smile:

    ehild
     
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