Two back-to-back diode PN junction of a bipolar junction transistor. Forward bias EB knot holes injected from the emitter region, CB in reverse bias junction barrier under the effect of an electric field to collector area, form the collector current IC. Most of the collector bias voltage between the emitter and is added on the reverse biased collector.
If the transistor's emitter current amplifying coefficient β =IC/IB=100, collector current IC= beta *IB=10mA. If an alternating base stacking in the bias circuit for small current IB, appears in the collector circuit a corresponding alternating current IC, c/IB= beta, bipolar transistor's current amplification is realized.