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Magnetic Force of sodium ions

  1. Sep 23, 2009 #1
    1. The problem statement, all variables and given/known data
    Sodium ions (Na+) move at 0.844 m/s through a bloodstream in the arm of a person standing near a large magnet. The magnetic field has a strength of 0.259 T and makes an angle of 59.0° with the motion of the sodium ions. The arm contains 95.0 cm^3 of blood with a concentration of 2.50 X 10^20 Na+ ions per cubic centimeter. If no other ions were present in the arm, what would be the magnetic force on the arm?



    2. Relevant equations
    F=qvBsin(theta)


    3. The attempt at a solution
    F= q(.844m/s)(.259T)(sin59)
    Thats as far as I have gotten. I am guessing that I need to use the volume of blood and concentration of ions to find the charge but I am not sure how to do so and have looked all through my text book for help.
     
  2. jcsd
  3. Sep 23, 2009 #2

    kuruman

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    If there are 2.5x1020 ions in 1 cm3, can you find how many ions are in 95 cm3?

    If the force on one ion is (as you say) F= q(.844m/s)(.259T)(sin59), can you the total force on all the ions in the 95 cm3?
     
  4. Sep 24, 2009 #3
    do i just multiply 95 by 2.5X10^20?
     
  5. Sep 24, 2009 #4

    kuruman

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    What do you think?
     
  6. Sep 24, 2009 #5
    well i tried that and once i worked it out the solution was wrong so im guessing that was incorrect.
     
  7. Sep 24, 2009 #6

    kuruman

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    Multiplying these two numbers is the correct thing to do. Whether you carried out the actual calculation correctly by pushing the right buttons on your calculator is another issue. If you show your calculation and the numbers you got, maybe someone will be able to figure out where you went wrong.
     
  8. Sep 24, 2009 #7
    ok well i multplied the two numbers and got: 2.375X10^22. however once i plugged this into the equation to deteremine the magnetic force i got 4.45X10^21 which is incorrect so im still unsure where i went wrong?
     
  9. Sep 24, 2009 #8
    dq=density*volume; That also helps
     
  10. Sep 24, 2009 #9

    kuruman

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    You are not showing your calculation, just the result. Show how you multiplied, added, divided these numbers.
     
  11. Sep 24, 2009 #10
    (95)(2.5X10^20)=2.375X10^22

    (2.375X10^22)(.844)(.259)(sin59)= 4.4X10^21
     
  12. Sep 24, 2009 #11

    kuruman

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    You need to redo your calculation. First off, the calculation as you show it above does not give 4.4x1021. Secondly, you did not include the charge on the ion.
     
  13. Sep 24, 2009 #12
    well i re-did my calculation and every way i work it i still get that same answer. and i am not sure what you mean by calculating the charge on the ion.
     
  14. Sep 25, 2009 #13

    kuruman

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    Look at the equation you posted:

    F= q(.844m/s)(.259T)(sin59)

    What does q stand for? Answer: The charge on the ion. Uncharged particles experience no force in a magnetic field whether they are moving or not.
     
  15. Sep 25, 2009 #14
    So how do I find q?
     
  16. Sep 25, 2009 #15

    kuruman

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    What is the charge on a singly ionized atom (Na+)?
     
  17. Sep 26, 2009 #16
    im clueless
     
  18. Sep 26, 2009 #17

    kuruman

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  19. Sep 26, 2009 #18
    The total number of atoms/particles/whatever times the charge of each one.

    The charge of an electron is http://lmgtfy.com/?q=charge+of+electron

    A "singly ionized atom" means that a single electron has been lost. A sodium atom has 11 electrons. A singly ionized sodium atom has 10 electrons. Since it has 11 protons, it has a net charge of +e, where e is given by the charge of the electron in the link above.
     
  20. Sep 26, 2009 #19
    q is in coulombs. How many Na+ ions are there in 1 coulomb?
     
  21. Sep 26, 2009 #20

    kuruman

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    6.25x1018.
     
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