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QPages 352-354: Q15: HC Verma: Concepts of Physics - Volume 2 Electric Current through Gases Pages 352-354: Q15 Solution: The dynamic plate resistance of a triode valve is . Find the…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students frequently treat the given dynamic plate resistance as a constant Ohmic value and apply ΔI = ΔV/r for a finite voltage change, forgetting that rₚ = dV/dI is defined only at a specific bias point for infinitesimal variations. Use it only for small‑signal changes; for larger ΔV the plate characteristic must be consulted.

The dynamic plate resistance of a triode valve is 10 kΩ10 \text{ k}\Omega. Find the change in the plate current if the plate voltage is changed from 200 V to 220 V.

Step-by-Step Verified Solution

**Answer:** Change in plate current ΔIp=2 mA\Delta I_p = 2 \text{ mA}. **Step-by-Step Explanation:** Given: rp=10 kΩ=104Ωr_p = 10 \text{ k}\Omega = 10^4 \Omega, ΔVp=220−200=20\Delta V_p = 220 - 200 = 20 V.
ΔIp=ΔVprp=20104=0.002 A=2 mA\Delta I_p = \frac{\Delta V_p}{r_p} = \frac{20}{10^4} = 0.002 \text{ A} = 2 \text{ mA}

All Questions in this Chapter

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