triode, also known as bipolar junction triode, is equivalent to two back-to-back diode pn junction. in the forward biased eb junction, holes are injected into the base region from the emitter, and most of the holes can reach the boundary of the collector junction, and reach the collector area under the action of the barrier electric field of the reverse biased cb junction to form the collector current ic. in the common emitter transistor circuit, the emitter junction is positively biased in the base circuit, and its voltage drop is very small.
there is a voltage drop vrc = 10ma * 500 ω = 5v on the collector load resistance of 500 ω, while the voltage drop between the collector and the emitter of the transistor is vce = 5v. if an alternating small current ib is superimposed in the base bias circuit, a corresponding alternating current ic will appear in the collector circuit with c / ib = β, which realizes the current amplification of bipolar transistor.
most of the applied bias voltage between the collector and the emitter is applied to the reverse biased collector junction. because vbe is very small, the base current is about ib = 5v / 50k ω = 0.1ma. if the common emitter current amplification factor β = ic / ib = 100, collector current ic = β * ib = 10ma.