Charge on a point in three different locations with a thin semicircular rod

  • Thread starter swagadoo
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  • #1
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Homework Statement


A thin semicircular rod is broken into two halves, the top half has a total charge +Q uniformly distributed along it, and the bottom half has a total charge -Q uniformly distributed along it.
http://imgur.com/tObt2V0

Homework Equations


Indicate the direction of the net electric force on a positive test charge placed in turn at points A, B, C.


The Attempt at a Solution


Had A's force vector pointing down and to the right, same with b and C pointing down and to the left but I am not sure about my answers.

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
haruspex
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Think about the forces in the horizontal and vertical directions separately. E.g. for A, compare the horizontal forces (i.e. along the line AB) exerted by the two quadrants.
 
  • #3
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I can't really visualize it but my guess is that the horizontal component of +Q would be to the left and the -Q would have a horizontal component equal and opposite so to the right. The vertical component of +Q on the charges would be down, same with the -Q charge.
 
  • #4
haruspex
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Exactly so. So the resultant force is in which direction?
 
  • #5
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Down and to the right. Would it be the same for both A and B. And C would be down and to the right?
 
  • #6
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or is the resultant straight down?
 
  • #7
fgb
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If the horizontal components are opposite (and equal in magnitude, since all distances are the same for the + and for the - quadrant), don't they cancel each other?
 
  • #8
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If the horizontal components are opposite (and equal in magnitude, since all distances are the same for the + and for the - quadrant), don't they cancel each other?
yeah thats what im thinking
 
  • #9
fgb
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Yeah, so the resultant is straight down, like you said :)
 
  • #10
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So all of the points; A,B, and C would have the same vector pointing down?
 
  • #11
fgb
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The magnitude of said vector would change according to distance from the point to the quadrants (i.e., the vector is smaller for point A than for point B), but it is indeed straight down for three points :)
 
  • #12
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Thank you very much.
 

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