Verified Solution • 2025–26 Session moderate

QPages 395-396: Q24: HC Verma: Concepts of Physics - Volume 2 X-Rays Pages 395-396: Q24 Solution: Continuous X-rays are made to strike a tissue paper soaked with …

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often read the plotted wavelength in Å or nm and plug it directly into ν=c/λ without converting to meters, producing a frequency off by 10⁹–10¹⁰ and a wildly incorrect atomic number. Always convert the wavelength to metres before using ν=c/λ, then apply $Z=1+\sqrt{\nu/(25\times10^{14})}$.

Continuous X-rays are made to strike a tissue paper soaked with polluted water. The incoming X-rays excite the atoms of the sample by knocking out the electrons from the inner shells. Characteristic X-rays are analysed and the intensity is plotted against the wavelength. Assuming that only

K_\alpha

intensities are detected, list the elements present in the sample from the plot. Use Moseley's equation

\nu = 25 \times 10^{14} \text{ Hz})Z - 1)^2

. Use Planck constant

h = 6.63 \times 10^{-34} \text{ Js} = 4.14 \times 10^{-15} \text{ eVs}

, speed of light

c = 3 \times 10^8 \text{ m/s}

.)

Step-by-Step Verified Solution

**Answer:** The elements present are determined from the wavelengths using Moseley's law. **Step-by-Step Explanation:** Moseley's equation:

\nu = 25 \times 10^{14}(Z - 1)^2

Hz. From the plot of intensity vs wavelength, identify the wavelengths of the

K_\alpha

peaks. For each wavelength, compute

\nu = c/\lambda

, then

Z = 1 + \sqrt{\nu/(25 \times 10^{14})}

. Identify the elements from their atomic numbers.

All Questions in this Chapter

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