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Homework Help: Difficult expert magnetism problem

  1. Mar 28, 2010 #1
    1.In a television set, electrons are accelerated from rest through a potential difference in an electron gun. They then pass through deflecting plates before striking the screen. (a) Determine the potential difference through which the electrons must be accelerated in the electron gun in order to have a speed of 6.0 x 107 m/s when they enter the deflecting plates.

    The pair of horizontal plates shown to the right is used to deflect electrons up or down in the television set by placing a potential difference across them. The plates have a length of 0.0400 m and a separation of 0.012 m, and the right edge of the plates is 0.500 m from the screen. A potential difference of 200.0 V is applied across the plates, and the electrons are deflected toward the top of the screen. Assume the electrons enter the plates with a speed of 6.0 x 107 m/s and the fringing at the edges of the plates and gravity are negligible.
    (b) Which plate in the pair must be at the higher potential (more positive) for the electrons to be deflected upward? Justify your answer.
    (c) Considering only an electron’s motion as it moves through the space between the plates, answer the following:
    i. The time for the electron to move through the plates.
    ii. The vertical displacement of the electron while it is between the plates.
    iii. Why it is reasonable to ignore gravity.
    iv. Describe the path of the electrons from when they leave the plate until they hit the screen. State a reason for your answer.

    The diagram is found here: http://es.tinypic.com/r/2ihmfcn/5

    Any help is appreciated.
  2. jcsd
  3. Mar 28, 2010 #2


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    Homework Helper

    For this part, consider conservation of energy, the energy the potential difference supplies is converted to kinetic energy.
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