UPSC Combined Geo-Scientist, Mains · 2018 · Mains Paper II
Q1(d). FCC particle count
Question
Estimate the number of particles per unit cell of an fcc crystal.
Answer in brief
An fcc conventional unit cell contains four particles.
Key points
- Eight corner particles are shared by eight cells each, contributing 8(1/8)=1 particle.
- Six face-centred particles are shared by two cells each, contributing 6(1/2)=3 particles.
- The total is 1+3=4. This count concerns lattice points occupied by single particles.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
CoversFCC particle countSolid state
All parts of Question 1
- 1(a) Equal molecular speeds5 marks
- 1(b) Fugacity under repulsion5 marks
- 1(c) Wetting of glass5 marks
- 1(d) FCC particle count5 marks
- 1(e) Joule–Thomson cooling5 marks
- 1(f) Gibbs and Helmholtz changes5 marks
- 1(g) Equilibrium-constant conventions5 marks
- 1(h) Very dilute hydrochloric acid5 marks
- 1(i) Pressure controlling boiling5 marks
- 1(j) Primary kinetic salt effect5 marks
- 1(k) Heat of spontaneous adsorption5 marks
- 1(l) Conductivity as an intensive property5 marks
- 1(m) Anthracene photodimerization5 marks
- 1(n) Particle-in-a-box eigenvalue5 marks
- 1(o) Second Balmer line5 marks
- 1(p) Normal-mode counts5 marks