State three operating regions of the transistor

 (I) Active region : EB junction is forward biased and CB junction is reversed biased. Transistor in this region operates as an amplifier.

(II) Saturation region : Both junctions of the transistor are forward biased. In this state transistor behaves as a close switch.

(III) Cut-off region : Occurs when both junctions of the transistor are reverse biased. In this state transistor behaves as an open switch.