Question 7.SP.18: For a triode with plate characteristics given by Fig. 7-8, f......

(a) The perveance can be evaluated at any point on the v_G = 0 curve.   Choosing the point with coordinates i_P = 15  \text{mA} and v_P = 100  \text{V}, we have, from (4.9),
i_{P} = \kappa(v_{P} + \mu v_{G})^{3/2}                  (4.9)
\kappa = {\frac{i_{P}}{v_{P}^{3/2}}} = {\frac{15  \times  10^{-3}}{100^{3/2}}} = 15\,\mu\mathrm{A}/\mathrm{V}^{3/2}

(b) The amplification factor is most easily evaluated along the v_P axis.    From (4.9), for the point i_P = 0,  v_P = 100  \text{V},  v_G = -4  \text{V}, we obtain
\mu = -{\frac{v_{p}}{v_{G}}} = -{\frac{100}{-4}} = 25