Under normal use of transistors, the emitter is forward- biased and the collector is reverse-biased. Can either of these biasing be changed? Explain.

What is an $n-p-n$ transistor? Give its symbol and describe its working. Why is it more useful in comparison to $p-n-p$ transistor?

Drawing a labelled circuit diagram, explain how a $p-n-p$ transistor can be used as an amplifier in common-emitter configuration? Derive expression for its voltage-gain.

Draw a labelled circuit diagram of common-emitter type transistor ($n-p-n$ or $p-n-p$) amplifier showing the biasing correctly.