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QPage 351: Q1: Electric Current through Gases Solutions — HC Verma: Concepts of Physics - Volume 2

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often assume that decreasing gas pressure always increases electrical conduction, overlooking that below a certain pressure the particle density becomes too low to sustain ionisation; the current follows a Paschen‑type curve with an optimal pressure, not a simple monotonic rise.

Why is conducting easier in gases if the pressure is low? Will the conduction continue to improve if the pressure is made as low as nearly zero?

Step-by-Step Verified Solution

**Answer:** Conduction is easier at low pressure because the mean free path of electrons is longer, reducing collisions. If pressure is made nearly zero, conduction will not continue to improve; it will eventually stop because there are too few gas molecules to ionise. **Step-by-Step Explanation:** At low pressure, gas particles are widely spaced, so electrons can travel longer distances without colliding. This allows them to gain more energy from the electric field and cause ionisation, sustaining the discharge. If the pressure is reduced to nearly zero, the number of gas molecules becomes negligible. Without molecules to ionise, the discharge cannot be sustained, and the current drops to zero .

All Questions in this Chapter

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