Coulomb's law in Electric Fields question (F) [PLEASE HELP]

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    I don't understand how part d produces the answer of F as it say is in the answers but I get all of the others.
    Why is this the case?

    Using the formula, I got F is preportional to Q/r but how is this giving the answer F.
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    It is predictable that the force F will be directly proportional to the charge Q and inversely proportional to some function of the distance r (I seem to remember it is r squared) between them (of course, the force has to be lower when the particles are further apart).

    a) the charge is 3Q instead of 2Q so the force (no change in r) = 1.5F

    b) the charge is double the one in example ANSWER = 2F

    c) charge still 4Q distance 2r (effect of distance (inverse) = 2 squared = 4 times, but inverse = quarter ANSWER: 2 X 1/4 = 0.5F

    d) charge = 2 X root of Q = root of Q as much as original; sep-n = root of r so effect = r/root of r inversely = 1/root of r i.e. 1/r to power -2 = r squared; total multiple = root X square: ANSWER = F

    Hope this helps AND hope I am right!!
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    (Original post by macpatelgh)
    It is predictable that the force F will be directly proportional to the charge Q and inversely proportional to some function of the distance r (I seem to remember it is r squared) between them (of course, the force has to be lower when the particles are further apart).

    a) the charge is 3Q instead of 2Q so the force (no change in r) = 1.5F

    b) the charge is double the one in example ANSWER = 2F

    c) charge still 4Q distance 2r (effect of distance (inverse) = 2 squared = 4 times, but inverse = quarter ANSWER: 2 X 1/4 = 0.5F

    d) charge = 2 X root of Q = root of Q as much as original; sep-n = root of r so effect = r/root of r inversely = 1/root of r i.e. 1/r to power -2 = r squared; total multiple = root X square: ANSWER = F

    Hope this helps AND hope I am right!!
    Sorry I do not understand d)

    The charges are now root(Q).
    There are 2 x root(Q).

    The radius is root(r)
    This means that F is preportional to root(r) squared

    How does this equal F, which is the correct answer like you have said?
    Sorry the notation I cannot follow very well
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    Give me 10 min- let me give you proper maths eq-s in MS Word.
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    Hi sorry for delay: there appears to be no "Proportional to" symbol in Word in Insert > Symbol NOR in Insert > Equation!!

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    somehow turned 90 deg!!
 
 
 
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