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B Graphs of Gravitational Potential and Field Strength

  1. Mar 30, 2016 #1
    Hi all, I am very confused about the graphs of gravitational potential and gravitational field strength...

    I know that both gravitational field (g) and electric field strength (E) are negative gradient of their corresponding potential (Vg and Ve). If so, shouldn't g and Vg graph look very much similar to E and Ve graph? However, most graphs regarding g and Vg show that graph of g exist in the first quadrant while that of Vg exists in the fourth quadrant.

    But for electric potential and field, the graphs of both quantity exist in the first quadrant. I find this very confusing as both relationships (g/Vg and E/Ve) are essentially the same.

    Any explanation would be appreciated. Thanks!
     
  2. jcsd
  3. Mar 30, 2016 #2
    the gravitational potential is defined by the work done in bringing an unit mass from infinity to the point at which it is defined.
    whereas the electric potential is defined as the work done in bringing an unit positive charge from infinity to the point at which it is being defined.
    so naturally the work done is -ve as the field does the work in case of gravity as it attracts the mass.
    but in case of electric field the work done is +ve as it is being brought against the repulsive force field.
    therefore the potential will have a +sign in case of electric field and -ve sign in case of gravitational field and when you calculate field intensity the same feature will move on.
     
  4. Mar 30, 2016 #3
    Thanks for the explanation. But it seems that we are taking for granted the fact that the electric field is produced by a positive charge? What if the field is produced by a negative charge so that the field will have the same direction gravitational field? Will the Ve graphs look similar to Vg graph in this case?
     
  5. Mar 30, 2016 #4
    general physical parameters are defined in a field of force and if one takes field to be directed in either +ve or -ve x direction ,then the potential nature will get affected - so for special situations any similarity/dissimilarity can happen but as the forces are very different in magnitude their graphs will look much different if drawn on same scale. many a time conventions are well established. i think we always take field to be in +ve x direction going to zero at infinity.
     
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