Semiconductors theory understanding nightmare1

  • Thread starter nhrock3
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  • #1
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beg3o5.jpg

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
??
 
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Answers and Replies

  • #2
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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?
 
  • #3
415
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thanks :)

this is only the first question among many
to understand 4 chapters
thanks again :)
 
  • #4
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what is N?
in the N/V formula
 
  • #5
245
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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.
 
  • #6
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ok thanks :)
 

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