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Homework Help: Determination of charge/mass value in E field.

  1. Jun 17, 2006 #1
    I've been trying this out many times I just couldn't get the answer, I hope someone could help me out here.

    A stream of nuclear particles are travelling horizontally at 3.9 X 10^6 ms^-1 are deflected as it passes through a vacuum between 2 parallel plates which are 5mm apart and 40mm in length. The P.D between the plates is 3000V and the angle of deflection is 4.3 degrees. Calculate q/m of a particle.

    My working:

    I first found out the field strength between the plates: dV/dr = 3000/0.005 = 600000 Vm^-1.

    Then the time for which a particle is between the plates: 0.4/3.9 X10^6 = 1.0256 X 10^-7 s.

    To find acceleration of a particle vertically downwards in terms of q/m would be => qE = ma, => a=qE/m = 600000q/m.

    Horizontal velocity is after it leaves the E field would still be 3.9 X 10^6, while vertical velocity is vertical acceleration multiplied by the time, => (6.15 X 10^-3)(q/m) ms^-1.

    I've found all I could, how can I solve for q/m? I tried using the equations for linear acceleration but they all consists of q/m on both sides which I cannot make the subject to determine the value.

    Any help much appreciated.

  2. jcsd
  3. Jun 17, 2006 #2


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    tan(4.3) = vy/vx
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