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Homework Help: Concept problems. multi choice check my answers.

  1. Aug 8, 2006 #1
    Ok i am studing and the book doesn't give answers. Here are a few questions i gave. What do you think.

    I will list pictures and test.

    For pic/question 1 - Will the answer be
    d - roatating the loop 90 degree ?

    Would it make sense that since the magnetic field is going into the paper i would want the resistor (R) to be perpendicular to the Mag field ?

    Attached Files:

  2. jcsd
  3. Aug 8, 2006 #2
    question 2

    My answer would be
    d- induced magnetic field clockwise.

    Reasoning- using the right hand rule with the thumb (V) pointing down, my fingers would rotate around clockwise. :confused:

    Attached Files:

    Last edited: Aug 8, 2006
  4. Aug 8, 2006 #3
    Questions 3 (last one for tonight - tried)

    I would say that the answer is
    C- the element is an inductor

    Since the voltage leads and the current lags behind makes me choice this one.

    Attached Files:

  5. Aug 10, 2006 #4


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    Homework Helper

    Q1. Current will be induced in the loop if the magnetic flux throught the loop is changed. Flux incorporates both the strength of the magnetic field and the area that the field goes through.

    a) will cause a decrease in the amount of flux through the loop, since the area of the loop is reduced the amount of flux going throught the loop changes - which will induce an current throught the loop (any change in flux will induce a current, no matter if it decreases or increases)

    b) will decrease the flux through the loop since the magnetic field is decreased - again a change in flux

    c) will cause an increase in flux through the loop

    d) will present less area to the magnetic field to go through as it is rotated, so a flux decrease will result, which will induce a current throught it

    So all of the changes will induce a current in the loop.
    Last edited: Aug 11, 2006
  6. Aug 10, 2006 #5
    The answer is A. Use the right hand rule, with the magnetic field going perpendicular to the wire, out from the magnet (out from the centre of the circle), and you use the force opposing motion. When you do this, you will get the induced current going counter clockwise around the ring from the viewer's perspective.
  7. Aug 11, 2006 #6


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    Homework Helper

    Q2 This is an application of Lenz's law. The flux through the ring decreases as it falls downwards. The induced current should therefore be such that the magnetic field that it generates will cause the flux throught the ring to increase.
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