Dc Current Gain Common Emitter — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
DC Current Gain (Common Emitter) Valid for Bipolar Junction Transistors (BJT) configured in Common Emitter mode, operating specifically in the active region. The definition of current gain is the ratio of output current to input current. In Common Emitter configuration, the Base is the input and the Collector is the output. Thus, defined as the ratio of DC collector current (I C) to DC base current (I B). Transistor must be in the active region (Emitter-Base junction forward biased, Collector-Base junction reverse biased). Valid only for DC values, not small-signal AC analysis (though values are often close). Confusing Beta (Common Emitter) with Alpha (Common Base). Alpha is I C / I E. Assuming Beta is strictly constant; it varies with temperature and collector current. Applying this formula in the saturation or cut-off regions where the linear relationship does not hold.