Q. With a change of load resistance of a triode, used as an amplifier, from $50\ kilo\ ohms$ to $100\ kilo\ ohms$, its voltage amplification changes from 25 to 30. Plate resistance of the triode is
A) 25 $k\Omega$
B) 75 $k\Omega$
C) 7.5 $k\Omega$
D) 2.5 $k\Omega$
Explanation
(a) Voltage amplification $A_{v} = \frac{\mu}{1 + \frac{r_{p}}{R_{L}}}$
$\Rightarrow 25 = \frac{\mu}{1 + \frac{r_{p}}{50 \times 10^{3}}}\ \ \ \ \ \ \ \ \ \ \ldots(i)$
and $30 = \frac{\mu}{1 + \frac{r_{p}}{100 \times 10^{3}}}$ …(ii)
On solving equations (i) and (ii), $r_{p} = 25k\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.