Q.Mention the biasing conditions for normal operation of transistor amplifier.

Before any signal is applied, the biasing network sets steady DC values of collector current $I_C$ and collector-emitter voltage $V_{CE}$. This fixed point on the DC load line is the operating point or quiescent point (Q-point). When the AC signal arrives, all instantaneous values swing about this point.

For normal transistor-amplifier operation two biasing conditions must hold together: the base-emitter junction is forward biased (about 0.6-0.7 V for silicon, 0.2-0.3 V for germanium) and the base-collector junction is reverse biased. These keep the device in its active region where linear amplification occurs.

The position of the Q-point decides the quality of amplification. Placed at the centre of the load line, the current and voltage can swing symmetrically in both directions, giving faithful, undistorted amplification and the largest possible signal handling. Placed near saturation, the positive peaks are clipped; placed near cut-off, the negative peaks are clipped — both distort the output.

Because temperature and transistor-parameter changes tend to shift the Q-point, an emitter resistor $R_E$ is added. If $I_C$ rises, the larger drop across $R_E$ reduces the effective $V_{BE}$, which lowers the base current and brings $I_C$ back down. This DC negative feedback stabilises the operating point against drift.