Amplifier

Oscillators

Multi vibrators

Speed control of motors

Atomic bonding structure of atom

Existence of valance electrons in atom

Atomic weight of the atom of the material

Atomic number of the atom of the material

Boron

Arsenic

Antimony

Phosphorous

Base ground, emitter and collector positive

Base negative, emitter positive and collector negative

Base positive, emitter negative and collector positive

Base positive, emitter negative and collector negative

To reduce the distortion

To increase the amplification factor

To increase the output voltage gain

To increase the output current gain