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

The plate current in a triode valve is observed to be zero, even though its filament temperature is high. This situation is possible when

Options

  1. AV_g 0
  2. BV_g > 0 , V_p > 0
  3. CV_g > 0 , V_p < 0
  4. DV_g < 0 , V_p < 0

Correct answer

D. V_g < 0 , V_p < 0

Step-by-step solution

The plate current in a triode valve is determined by the effective potential V_ eff = V_p + V_g , where V_p is the plate voltage, V_g is the grid voltage, and is the amplification factor. The plate current I_p is zero when the effective potential is less than or equal to zero, i.e., V_p + V_g 0 . Let us analyze the given options: For V_g 0 , I_p = 0 is possible if the grid is sufficiently negative such that |V_g| V_p (cut-off condition). For V_g > 0 and V_p For V_g For V_g > 0 and V_p > 0 , the effective potential

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