Verified Solution • 2025–26 Session moderate

QPages 393-394: Q9: HC Verma: Concepts of Physics - Volume 2 X-Rays Pages 393-394: Q9 Solution: One of the following wavelengths is absent and the rest are…

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often forget that a Coolidge tube has a minimum (cut‑off) wavelength $\lambda_{\min}=\frac{hc}{eV}$; no X‑rays shorter than this can be emitted. Hence the only wavelength that can be absent is the smallest one listed, not the longest or a random choice.

One of the following wavelengths is absent and the rest are present in the X-rays coming from a Coolidge tube. Which one is the absent wavelength?

Multiple Choice Options

  • A 25 pm
  • B 50 pm
  • C 75 pm
  • D 100 pm

Step-by-Step Verified Solution

**Answer:** (a) 25 pm. **Step-by-Step Explanation:** The X-ray spectrum has a minimum wavelength __min. If 50, 75, and 100 pm are present, then 25 pm (which is smaller) is absent.

All Questions in this Chapter

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