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Semiconductors theory understanding nightmare1

  1. Mar 20, 2010 #1
    if we have a molecule or atom
    then if we take avogadros number amount of this unit
    then the amount will weight the atomic mass in grams.

    [tex]\rho _m/A[/tex]

    rho is the density
    A is the atomic mass

    why their dinviding gives us moles per cube cantimeter
    Last edited: Mar 20, 2010
  2. jcsd
  3. Mar 20, 2010 #2
    In general, looking carefully at the units tends to help me understand physics. (BTW, solid state physics was the hardest subject for me.)

    Anyway, we have this:

    [tex]n = 0.6022 \times 10^{24} \frac{Z \rho_m}{A}[/tex]

    Physicists have a nasty habit of leaving out units when they write equations in text books. That didn't stop the physicists in my EE department from marking my grade down when I forgot to put units on my test answers. YOU'LL GET YOURS ONE DAY PHYSICISTS!!!

    Let's add the units:

    [tex]n (#electrons) = 0.6022 \times 10^{24} \frac{#atoms}{mole} \frac{Z \frac{#electrons}{atoms}\rho_m \frac{mass}{cm^3}}{A \frac{mass}{mole}}[/tex]

    You can see how the units cancel now. Does that help?
  4. Mar 20, 2010 #3
    thanks :)

    this is only the first question among many
    to understand 4 chapters
    thanks again :)
  5. Mar 20, 2010 #4
    what is N?
    in the N/V formula
  6. Mar 20, 2010 #5
    Man, I can do anything these days without making an error. The correct units were:

    [tex]n \frac{electrons}{cm^3}= 0.6022 \times 10^{24} \frac{#atoms}{mole} \frac{Z \frac{#electrons}{atoms}\rho_m \frac{mass}{cm^3}}{A \frac{mass}{mole}}[/tex]

    To answer your last question:

    [tex]n = \frac{N(electrons)}{V(cm^3)}[/tex]

    Capital N is just the number of electrons and V is the volume.
  7. Mar 20, 2010 #6
    ok thanks :)
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