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Concepts Of Physics MCQ Edition [Volume 2]PhysicsElectric Current through Gases

A triode has a plate resistance of 8 k and a transconductance of 2.5 millimho . The plate voltage is increased by 48 V . If the plate voltage is held constant at this new elevated value, by how much must the grid voltage be reduced to restore the plate current to its initial value?

Options

  1. A3.6 V
  2. B2.4 V
  3. C1.2 V
  4. D4.8 V

Correct answer

B. 2.4 V

Step-by-step solution

Given: Plate resistance r_p = 8 k = 8 10^3 Transconductance g_m = 2.5 millimho = 2.5 10⁻³ mho Change in plate voltage V_p = 48 V The amplification factor is given by the product of plate resistance and transconductance: = r_p g_m = (8 10^3) (2.5 10⁻³) = 20 For a constant plate current ( I_p = 0 ), the relation between the change in plate voltage and the change in grid voltage is: = - V_p V_g Substituting the values: 20 = - 48 V_g V_g = - 48 20 = -2.4 V The negative sign indicates that the grid voltage must be reduc

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