How to Calculate α (alpha) of a Transistor



α (Alpha), the factor by which emitter current is multiplied to yield collector current, can be calculated in two ways.


1st Way to Calculate Alpha α
If the β of the transistor is known, α can be calculated very easily by the formula:



Formula for alpha of transistor

Example
If β of a transistor is 100, calculate the α of the transistor:

calculating alpha of transistor from beta example

2nd Way to Calculate Alpha α
If the collector current, Ic, and the emitter current, Ie, are known, then α can be calculated by the following formula:



alpha formula with collector current Ic and emitter current Ie

Example
If the collector current Ic= 7.95ma and the emitter current Ie=8ma, then alpha calculates out to be:



calculating alpha of a transistor from collector current ic and emitter current ie in a transistor


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