1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Magnetic field: the Banebridge velocity selector

  1. Feb 6, 2010 #1
    1. The problem statement, all variables and given/known data

    The electric field intensity between the plates of the Banebridge velocity selector (I am not a native English speaker …) is 120 [Volt/cm] and the magnetic field magnitude of both fields is 0.6 [Weber/m2].
    A singly charged Neon ion beam makes a radius of 7.28 [cm]. What is it's mass number.
    The result must be 21, 10 times smaller than mine.

    2. Relevant equations

    Velocity of beam: V=[itex]\frac{E}{B}[/itex]
    radius of the beam: [tex]R[m]=\frac{mV}{qB}[/tex]
    mass number=mass/proton mass: [tex]N=\frac{m}{m_{p}}[/tex]

    3. The attempt at a solution

    120[Volt/cm]=12,000[Volt/m]

    [tex]V=\frac{E}{B}=\frac{12,000}{0.6}=20,000[m/sec][/tex]

    [tex]R=0.728=\frac{mV}{qB}=\frac{m*20,000}{1.602\ \times\ 10^{-19}*0.6}\Rightarrow m=3.5\ \times\ 10^{-25}[/tex]

    [tex]N=\frac{m}{m_{p}}=\frac{3.5\ \times\ 10^{-25}}{1.672\ \times\ 10^{-27}}=209[/tex]
     

    Attached Files:

  2. jcsd
  3. Feb 6, 2010 #2
    what is your questions exactly?
     
  4. Feb 6, 2010 #3
    My result is 10 times bigger, according to the book and the periodic table of elements, it should come out 20.9
     
  5. Feb 6, 2010 #4
    I cant see whats wrong with your solution , it seems okay ..
     
  6. Feb 6, 2010 #5
    Thanks for your effort, Ihope I'll get another answer before I decide there was a mistake in the book. By the way, it's taken from a translation to Sears & Zemansky, 1964...
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook