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Homework Help: Charged Particles in Magnetic Fields

  1. Feb 3, 2008 #1
    1. An ionized deuteron (a particle with a + e charge) passes through a velocity selector whose perpendicular magnetic and electric fields have magnitudes of 40 mT and 8.0 kV/m, respectively. Find the speed of the ion

    2. When a charge particle moves in a velocity selector, both electric field and magnetic field are there.

    Any charged particle in an electric field will feel a force proportional to the charge and field strength such that F = qE , where F is force, q is charge, and E is electric field. Similarly, any particle moving in a magnetic field will feel a force proportional to the velocity and charge of the particle. The force felt by any particle is then equal to F = qv X B , where F is force, q is the charge on the particle, v is the velocity of the particle, B is the strength of the magnetic field, and X is the cross product. In the case of a velocity selector, the magnetic field is always at 90 degrees to the velocity and the force is simplified to F = qvB in the direction described be the cross product.

    F = qE and F = qvB

    So, qE = qvB

    V = E/B

    Setting the two forces to equal magnitude in opposite directions it can be shown that V = E/B . Which means that any combination of electric (E) and magnetic (B) fields will allowed charged particles with only velocity (v) through.

    3. E = 8 KV/m = 8 x 103 V/m

    B = 40 mT = 40 x 10-3 T

    V = 8 x 103 x 40 x 10-3

    V = 320 m/sec


  2. jcsd
  3. Feb 3, 2008 #2

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    Why have you multiplied E and B?

    (I really don't feel that you should copy and paste almost the entire page from Wikipedia, along with the grammatical and spelling mistakes. Write it yourself.)
  4. Feb 3, 2008 #3

    If I should not multiply E and B, what
    should I do instead to get the correct answer?
  5. Feb 3, 2008 #4

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    This is from your post. What do you think you should do to get v?
  6. Feb 6, 2008 #5
    Given that B =40 x 10 ^-6
    E = 8000 V/m

    have Bev = eE

    v = E/B

    v= 8000/ 40 x 10^-6
    v= 2 x 10^8m/s
  7. Feb 6, 2008 #6

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    Is the value of B you have used here is correct?
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