Question

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 kΩ
• B. 75 kΩ
• C. 7.5 kΩ
• D. 2.5 kΩ

Answer 1

Answer: (A)

25 kΩ

Answer 2

Voltage amplification $A_{v} = \frac{\mu}{1 + \frac{r_{p}}{R_{L}}}$

$\Rightarrow 25 = \frac{\mu}{1 + \frac{r_{p}}{50 \times 10^{3}}}$ ......(i)

And $30 = \frac{\mu}{1 + \frac{r_{p}}{100 \times 10^{3}}}$ ......(ii)

an solving equation (i) and (ii), $r_{p} = 25k\Omega.$