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Homework Help: Hibbeler 13-34

  1. Mar 2, 2014 #1
    1. The problem statement, all variables and given/known data

    In the cathode-ray tube, electrons having a mass m
    are emitted from a source point S and begin to travel
    horizontally with an initial velocity v0. While passing
    between the grid plates a distance l, they are subjected to a
    vertical force having a magnitude eV/w, where e is the
    charge of an electron, V the applied voltage acting across
    the plates, and w the distance between the plates. After
    passing clear of the plates, the electrons then travel in
    straight lines and strike the screen at A. Determine the
    deflection d of the electrons in terms of the dimensions of
    the voltage plate and tube. Neglect gravity which causes a
    slight vertical deflection when the electron travels from S to
    the screen, and the slight deflection between the plates.

    See attachment for picture

    2. Relevant equations

    ∑Fy = may

    vy = ayt

    3. The attempt at a solution

    By Newton's 2nd Law,

    ay = eV/mw from 0 to l

    By kinematics t1 = l/v0
    t2 = t1 + L/v0 = l/v0 + L/v0

    From 0 to l, by kinematics:

    y1 = 1/2*eV/mw*(l/v0^2)
    (v1)y = eV/mw*l/v0

    Hence, from l to L where ay is zero

    y2 = d = 1/2*eV/mw*l^2/v0^2 + eV/mw*L/v0

    It appears the solution is missing the left term I keep getting, any idea why?

    Attached Files:

    Last edited: Mar 2, 2014
  2. jcsd
  3. Mar 2, 2014 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    The solution is missing that term because they are neglecting the slight deflection between the plates, as mentioned at the end of the problem statement.
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