Showing Revision 1 created 10/27/2012 by Amara Bot.

1. Title:
   08ps-07 Cathode Ray Tube
2. Description:

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   For this problem, we're going to be talking about cathode ray tubes.
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   And it may or may not be a name that means something to you depending on how old you are.
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   Cathode ray tubes used to be main way we got televisions to work
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   before we had LED, LCD, and plasma televisions.
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   And let's investigate how exactly these tubes work.
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   So on one end of the tube we have an electron here, and we give it some really large
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   initial velocity V₀ such that it shoots across this tube towards this green screen over here.
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    And when this electron hits the screen over here,
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    it temporary causes it to light up producing a dot on the screen.
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    Now you can imagine if we were able to draw lots of these dots on the screen
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    we could use it to draw images like this one here.
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    Well in order for us to be able to make dots on other parts of the screen,
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    we have to bend the path of the electron so it doesn't just go on a straight line.
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    And how can we bend the path of an electron? Well one easy way is with an electric field.
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    And we saw on the previous two questions that a great way to produce a nice
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    constant magnetic field is to have two parallel plates like these two.
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    When this negatively charged electron moves into this electric field,
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    it'll get pulled towards the positive plate directing it to this part of the screen.
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    And you could imagine if we wanted the electron to go down here,
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    we just switch the charges so the negative charges were up here
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    and the positive charges were down here.
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    This means we can control what part of the screen the electron hits and therefore
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    lights up just by changing the strength and direction of this electric field here.
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    For this problem you're going to tell me how strong I should make this
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    electric field such that this electron gets bent a distance away from the center
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    from its straight line path of Δy.
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    You should assume that the electron is in the magnetic field
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    for a total distance of 0.5 m and we want the deviation away
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    from the center of Δy to be equal to 0.1 m.
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    We'll also assume that the electron enters the field with an initial velocity of 1x10⁷ m/s.
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    You will also need the charge and mass of the electron, which I have provided here.
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    Now a few quick notes. You'll notice that the speed here is really large
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    and the super student among you might notice that it's actually getting close
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    to being the speed of light.
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    If you heard anything about the theory of relativity, you might know that as we get
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    close to the speed of light strange things start to happen.
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    We won't worry about any of that in this problem now.
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    Just assume that everything behaves as we're used to.
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    Also note that even though I've drawn my field line so the arrows are pointing down
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    the electron is going to bend up because it has a negative charge
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    and we always draw the field lines in the direction a positive charge will move.
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    All right--so you can put your answer for the strength of the electric field
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    right here and put it in units of N/C--all right, good luck.