JEE Main 2016 · 10 Apr · Shift 1 · Physics Q29

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PhysicsSingle correct+4 / -1Question 29 of 90

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

Zero until about 0.6 V, then rising and levelling off at 0.01

Graph of 1/rᵢ (Ω⁻¹) against V_BE (V) from 0 to 1 V: zero until about 0.6 V, then rising steeply and levelling off just below 0.01.

Starting at 0.01 and falling to zero near 1 V

Nearly constant at 10, rising steeply near 1 V

Graph of 1/rᵢ (Ω⁻¹) against V_BE (V) from 0 to 1 V: nearly constant at 10, then rising steeply towards a vertical asymptote at 1 V.

Dipping from 0.1 to a minimum near 0.6 V and rising back

Graph of 1/rᵢ (Ω⁻¹) against V_BE (V) from 0 to 1 V: starting near 0.1, dipping to a minimum around 0.6 V and rising back towards 0.1.

Answer and worked solution

Official answer: A

Below the cut-in voltage (about 0.6 V for silicon) the base-emitter junction barely conducts, so $\frac1{r_i}\approx0$ . Above it the junction conducts and $\frac1{r_i}$ rises, levelling off as the bulk resistance takes over. Graph (1) shows this.

Topics:Transistors

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JEE Main 2016 · 10 Apr · Shift 1, Physics question 29