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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper II covers physical chemistry.

UPSC Combined Geo-Scientist, Mains · 2026 · Mains Paper II

Q1(c). First-order Bragg angle for the (110) planes

  • 5 marks
  • Topic: Solid state
  • Answered
Question

What is the angle of first order X-ray diffraction for 110-planes of a simple cubic lattice of edge length 800 pm when X-ray wavelength is 0.4 nm.

Answer in brief

θ=20.7^° (2θ=41.4^°).

The full model answer

Worked out step by step, as it should go in the answer booklet. The solution sheet follows it.

d₁₁₀=(a)/(√(h²+k²+l²))=(800)/(√2)=565.7 pmλ=0.4 nm=400 pm

nλ=2dθ (n=1): θ=(400)/(2(565.7))=0.3536θ=20.7^°

Model answer to Q1(c), 2026 Mains Paper II: solution page 4
Solution page 4 of 22
Read the whole 2026 solution2026 question paper

CoversBragg equationFirst-order Bragg angle for the (110) planes

All parts of Question 1