Forward Bias:

Assume that the bias at the base of an npn transistor is positive associative to the emitter, beginning at small levels and steadily rising. This is forward bias. When this bias is less than forward breakover, then no current flows. Though, whenever the voltage reaches forward breakover, then the E-B junction conducts current.

In spite of reverse bias at the base-collector (B-C) junction, the emitter-collector (E-C) current, more frequently termed as collector current and symbolized by I_C, flows whenever the E-B junction conducts. A small increase in the positive-polarity signal at the base, attended by a small increase in the base current I_B, causes a large rise in I_C. This is the principle by which a bipolar transistor can amplify the signals.