A realistic graph depicting the variation of the reciprocal of input… | JEE Main 2016 (10 Apr, Shift 1)

Q99JEE Main 2016 · 10 APR · SHIFT 1Difficult

Junction Transistor

A realistic graph depicting the variation of the reciprocal of input resistance in an input characteristics measurement in a common emitter transistor configuration is:

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Answer: (c)

Input characteristic: $I_B$ is almost zero until $V_{BE}$ reaches the knee (about 0.6 V), then rises sharply.
So $1/r_i = \Delta I_B/\Delta V_{BE}$ is nearly zero below 0.6 V, then rises and levels off at a finite value (a few hundred ohm to 1 k $\Omega$ input resistance, i.e. about $0.01\ \Omega^{-1}$ scale).
This is the S-shaped curve of option (a); option (c) starting at $10\ \Omega^{-1}$ and diverging at 1 V is unrealistic.
So the working gives (a).

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