We just studied basic semiconductors on the high school level and we ended on transistors and we got three notations alpha beta gamma which corresponds to three different transistor arrangement with common base emitter and collector, now surely there must be some reason why common emitter arrangements current amplification factor is called beta while common base is alpha and commin collector is gamma can someone tell me the historical reason for these assigned symbols or any physical interpretation?


1 Answer 1


The alpha, beta and gamma are not actually representing the same thing.

  1. In a common emitter, you input base current and take the output somehow related to collector current. So, Ic/Ib = beta becomes your current amplification ratio for common emitter.
  2. For a common base, you input to emitter and take output from collector. The emitter and collector currents are nearly equal. So the amplification ratio is alpha, which is a value very close to 1 but less than 1.
  3. In common collector configuration, you input the base current and get the output from emitter, so the ratio is Ie/Ib which is gamma, slightly higher than beta.

Ie = Ib + Ic
Ic = beta * Ib // common emitter 
Ie = gamma(beta+1) * Ib // common collector
Ic = alpha * Ie // common base

You may find this video helpful.

  • 1
    \$\begingroup\$ But that wasn't what i asked for i understand they represent different things i want to know why is no1 called alpha only, is there any significance to assigning that? \$\endgroup\$
    – SOSXX
    Dec 14, 2019 at 9:30
  • \$\begingroup\$ @SOSXX so you're asking something like "history of electronics"? \$\endgroup\$
    – muyustan
    Dec 14, 2019 at 9:32
  • 1
    \$\begingroup\$ On the very earliest transistors which were the point-contact type the only practical way to use them was as common-base and alpha could actually be more than unity up to about 2.5. \$\endgroup\$ Dec 14, 2019 at 11:57

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