In a transistor, the base current is about ______ of the emitter current. 

The Base current is typically 2% of the emitter or collector current for small-signal transistors. 

• The three terminals of BJT are the base, emitter, and collector.
• A very small current flowing between the base and the emitter can control a larger flow of current between the collector and emitter terminal.
• Emitter Current (IE) = Collector Current IC) + Base Current

Different current gains of BJT

1.) Common emitter current gain

In this configuration, the emitter terminal is grounded and the input is given to the base and the output is taken from the collector.

The relationship between base current IB, emitter current IE and collector current IC is given by:

lE = lB + lC

The current gain in common emitter configuration is:

It is the ratio of collector current to base current.

It is denoted by β.

2.) Common collector current gain

In this configuration, the collector terminal is grounded and the input is given to the base and the output is taken from the emitter.

It is the ratio of emitter current to base current.

It is denoted by γ.

3.) Common base current gain

In this configuration, the base terminal is grounded and the input is given to the emitter and the output is taken from the collector.

It is the ratio of collector current to emitter current.

It is denoted by α.

Also,