What is α (alpha) of a transistor?

α (alpha) of a transistor is the factor or value that an emitter current is multiplied by to give the value of the collector current.

If you have the value of the emitter current of a transistor circuit and you want to solve for the collector current, the emitter current is multiplied by α to give the collector current.

The formula for α is:

Formula for alpha of transistor

To calculate the collector current from the emitter current and α, the formula is:

collector current Ic formula using emitter current Ie and beta


If Ie=4ma and β=150, then the value of α and Ic are computed to be:

calculating alpha and collector current ic of a transistor