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JEE Main 2026 (22 Jan, Shift 1) · Atomic Models & Alpha-Particle Scattering

Atomic Models & Alpha-Particle Scattering question from JEE Main 2026 (22 Jan, Shift 1)

Q3JEE Main 2026 · 22 JAN · SHIFT 1Medium

Atomic Models & Alpha-Particle Scattering

7.9 MeV α7.9\text{ MeV }\alpha-particle scatters from a target material of atomic number 79. From the given data the estimated diameter of nuclei of the target material is (approximately) ______ m.

[14πϵ0=9×109 Nm2/C2\Bigg[\frac{1}{4\pi\epsilon_0} = 9 \times 10^{9}\text{ Nm}^2/\text{C}^2 and electron charge =1.6×10−19 C]= 1.6 \times 10^{-19}\text{ C}\Bigg]

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Answer: (b)

  1. Closest approach: r0=k(2e)(Ze)Kr_0 = \dfrac{k(2e)(Ze)}{K} with K=7.9 MeV=7.9×106eK = 7.9\text{ MeV} = 7.9\times10^6 e J.
  2. r0=9×109×2×79×1.6×10−197.9×106=2.88×10−14r_0 = \dfrac{9\times10^9 \times 2 \times 79 \times 1.6\times10^{-19}}{7.9\times10^6} = 2.88\times10^{-14} m.
  3. This estimates the nuclear radius, so diameter =2r0=5.76×10−14= 2r_0 = 5.76\times10^{-14} m.
  4. So the answer is (b).
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