phy 3 條mock mc 急

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  • 天同
    Lv 7
    7 年 前
    最佳解答

    19. The fringe separation should be 入v/z

    I don't think any one of the options is correct.

    20. There is no force acting on l2 as it is outside the magnetic field.

    I suppose the magnetic field is pointing into the paper, the magnetc force on l3 is upward by using Fleming's Left Hand Rule (Motor Rule).

    Since the magnetic force = NBIl

    Hence, the net force = mg - NBIl

    35. Since kinetic energy of recoil nucleus = E

    E = (1/2).(N-4)V^2 where V is the recoil speed

    V^2 = 2E/(N-4)

    By conservation of momentum,

    chnage of momentum of recoil nucleus = change of momentum of alpha

    (N-4)V = 4v where v is the speed of the alpha particle

    squaring on both sides,

    (N-4)^2V^2 = 16v^2

    v^2 = (N-4)^2V^2/16

    v^2 = [(N-4)^2/16].[2E/(N-4)]

    v^2 = (N-4)E/8

    kinetic energy of alpha particle

    = (1/2).(4)v^2

    = 2(N-4)E/8

    = (N-4)E/4

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