The transfer characteristics for a base biased transistor in CE configuration is as shown in the figure. For using transistor as an amplifier, it is used in:

region II

In the given graph,

Region (I) – Cut off region

Region (II) – Active region

Region (III) – Saturation region

For using transistor as a switch it is used in cut off region or saturation region.

For using transistor as a amplifier it is used in active region.