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QPage 351: Q9: HC Verma: Concepts of Physics - Volume 2 Electric Current through Gases Page 351: Q9 Solution: The cathode of a diode valve is replaced by another cathode of…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often incorrectly assume that thermionic emission depends only on temperature and material, leading them to predict the current remains unchanged. You must recognize that the total emission rate is proportional to the cathode's surface area, so doubling the area doubles the electron flux and the resulting plate current.

The cathode of a diode valve is replaced by another cathode of double the surface area. Keeping the voltage and temperature conditions the same, will the plate current decrease, increase or remain the same?

Step-by-Step Verified Solution

**Answer:** The plate current increases (doubles). **Step-by-Step Explanation:** The rate of thermionic emission is directly proportional to the surface area of the cathode. If the surface area is doubled while temperature and voltage remain the same, the number of emitted electrons per second doubles, so the plate current doubles .

All Questions in this Chapter

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