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what is pn junction?how we can forward biase to a transister?

PN junction is an interface between p type and n type semiconductors. A space charge region is created at junction. N type semiconductor has more concentration of electrons and p type semiconductor has more concentration of holes.

BJT which stands for Bipolar Junction Transistor can be of two types, either NPN or PNP. Biasing is the process in which external voltage is applied to transistor for different applications. Biasing can be of two types, one is forward biasing and other is reverse biasing. In case of forward biasing, transistor works as a closed switch and current flows through it.

How to forward bias a transistor:

Connect the collector to high voltage as compared to base and emitter is connected to low positive voltage source as compared to base. When voltage between base and emitter is increased more than or equal to 0.7 v, transistor is in forward biased mode.