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Homework Help: Rearange equations

  1. Apr 14, 2010 #1
    F = A Q1Q2/r2

    simple steps to make A the subject and the SI units i should use?
     
  2. jcsd
  3. Apr 14, 2010 #2
    can you please clarify your question?
     
  4. Apr 14, 2010 #3
    yes sorry i need simple steps to make a the subject of this equation
     
  5. Apr 14, 2010 #4
    this is coulombs law and i als need to use the correct SI unts to represent A

    F = force
    Q1 = Charge 1
    Q2 = Charge 2
    A is the constant
    and r2 is the sepeation
     
  6. Apr 14, 2010 #5
    Still not sure, but, well, if i guess correctly:

    0. F=A Q1Q2/r2 (i would expect to be r^2, but the steps are the same ;P) // multiply both sides by r2

    1. F*r2=A Q1Q2 // Divide both sides by Q1Q2 (or first by Q1, and then by Q2)
    2.F r2/Q1Q1=A
    3.A=Fr2/Q1Q2

    life can be that simple :P
    But i still believe it's r^2


    E: Units A=[N*m^2/C^2]=[kg*(m/s^2)*m^2/(As)^2]=[kg*m^3/(A^2*s^4)]... I hope it's fine XD
     
  7. Apr 14, 2010 #6
    well, im not sure if i understood your question ..

    anyway .. you know that:

    F : is measured in newton (N)
    r : is measured in meter (m)
    Q1, Q2 : in columb (c) ..

    so the constant A should have a unit of ( N * m^2 / c^2) , which usually is taken as 9x10^9
     
  8. Apr 15, 2010 #7
    great thankyou very much, how do you work out Nm^2 / c^2 are the SI units and what does Nm^2 actualy stand for, i am struggling to understand what a constant actualy is and how it is measured?
     
  9. Apr 15, 2010 #8
    Newtons and Coulombs are not SI units. I mean.. SI consists of just a couple of basic units:
    kg
    m
    s
    A
    cd
    K
    mol

    All other units derive from those 7. Hence if you want "pure" SI units, take a peek at my previous post.
     
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