Question

Assertion: A transistor amplifier is common emitter configuration has a low input impedence.
Reason: The base to emitter region is forward biased.
A. If both the assertion and reason are true and reason is a true explantion of the assertion.
B. If both the assertion and reason are true but the reason is not true the correct explantion of the assertion.
C. If the assertion is true but reason false
D. If both the assertion and reason are false.

Answer 1

Correct Answer - B
In transistor the emitter-base junction is forward bias while the base-collector junction is given a large reverse biase. Under forward bias the charge carriers move towards base causing the flow of current.
The following shows the circuit of a common-emitter amplifier circuit using an `n-p-n` transistor. The input (base-emitter) circuit is forward biased by a low voltage battery `V_(BE)`, so that the resistance of the resistance of the input circuit is small.

The output(collector -emitter) circuit is reverse biased by means of a high voltage battery so that resistance of output is high. The weak input `AC` signal is applied across the base-emitter circuit and the amplified output signal is obtained across the collector-emitter circuit. Input impedence of common-emitter configuration
`=((DeltaV_(BE))/(DeltaI_(B)))V_(CE)`=constant
Here, `DeltaV_(BE)`=voltage across base and emitter, `DeltaI_(B)`=base current of the order of few micro ampere.