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Homework Help: Physics Fundamentals : CRO and Potential Divider

  1. Jun 30, 2014 #1
    1. The problem statement, all variables and given/known data

    The figure shows 2 terminals M and N of a potential divider connected to a 6V battery. The circuit is connected to a Cathode-ray Oscillator.

    The y-gain is 2V per division and timebase setting is 1.0ms per division.

    (a) Describe in details what happens as the terminal is moved at a uniform speed from N to M.
    (b) Draw the final reading of the final trace that is shown the CRO as N is moving towards M.

    2. Relevant equations


    3. The attempt at a solution

    (a) As terminal N is moving towards M, there will be an increased in e.m.f, the results in a higher reading on the tracd

    (b) http://i.imgur.com/bldLWjF.jpg
    This is my attempt.

    Please correct me if I make any mistakes. Thank you!
    Last edited: Jun 30, 2014
  2. jcsd
  3. Jun 30, 2014 #2


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    Is that the question exactly as posed? Its seems slightly badly worded to me.

    Is there any mention of the time base setting on the oscilloscope? You have assumed that it's fast and on continuous sweep - you are probably right - but what if the horizontal time base is say 5 seconds per division and you move the slider?
  4. Jun 30, 2014 #3
    Hi. Yes. It is exactly as worded.

    I am sorry I forgot to typed the y-gain and time base into the question. I edited it on the front post now.

    The y-gain is 2V per division, time base setting is 1.0ms per division.

    I want to know if my understanding is correct. If I move the potential divider from point N to point M uniformly, there will be an increased e.m.f. An increased e.m.f will show a higher (positive) horizontal reading on the CRO. This is because it is connected to a direct current and not an alternating current.

    Is my understanding correct? I was thinking about your question. What if the timebase setting is 5seconds per division. Is it going to affect the trace on the CRO? If I am not wrong, the timebase will not affected by the increase or decreased in e.m.f right? No matter what it wil always be in a horizontal line as it is connected to a direct current. (6V battery)

    Thank you!
  5. Jun 30, 2014 #4


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    If the timebase was 5 seconds per division and there were 10 divisions across the width of the screen, how long would it take the trace to cross the screen once? What wpuld you see if you moved the potentiometer terminal quickly while the timebase was crossing the screen slowly?
  6. Jun 30, 2014 #5

    Am I right to say this:
    If the timebase setting was 5 seconds per division and the terminal is moved quickly, I will see a trace that was lower initially and then a gradual slope upwards (positive gradient) then a constant horizontal line at its new higher trace reading.

    Am I understanding it correctly?
    Thank you!
  7. Jul 1, 2014 #6


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    So the answer you gave in the original post is correct. However it does say describe in detail so you might like to mention that you will see a horizontal line on the scope that also moves upwards at a constant velocity until it reaches 6V.

    What you see depends on the type of scope. On a cheap basic scope you would see a point/dot that moves in a straight line at an angle to the horizontal until it reaches 6V, then it moves horizontally. If it's a storage scope then yes you would see a trace/line that follows the same path.
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