A triode has a plate resistance of 10 k and an amplification factor of 20 . Initially, it is operated at a plate voltage of 250 V and a grid voltage of -7.5 V , yielding a plate current of 10 mA . The grid voltage is subsequently adjusted to -5.0 V , increasing the plate current to 15 mA . To what value must the plate voltage be altered to bring the plate current back to 10 mA ?

Step-by-step solution

For a triode, the change in plate current I_p is given by: I_p = V_p r_p + g_m V_g where g_m = r_p . To bring the plate current back to its initial value of 10 mA , the net change in plate current from the initial state must be zero ( I_p = 0 ). Substituting I_p = 0 into the equation: 0 = V_p r_p + r_p V_g V_p = - V_g The change in grid voltage from the initial state is: V_g = -5.0 - (-7.5) = 2.5 V Using the given amplification factor = 20 : V_p = -20 2.5 = -50 V The new plate voltage is: V_p = 250 - 50 = 200 V Alt