UPSC Combined Geo-Scientist, Mains · 2020 · Mains Paper II
Q1(n). Wavelength and the einstein
Question
Does an einstein depend on electromagnetic wavelength? Explain with an expression.
Answer in brief
One einstein always means one mole of photons; its energy is wavelength-dependent, Eₑᵢₙₛₜₑᵢₙ=NAhc/λ.
Key points
- The photon number is fixed at Avogadro' s number, independent of colour or wavelength.
- Each photon has energy hν=hc/λ, so the energy represented by that photon amount varies inversely with wavelength.
- Doubling wavelength halves the energy per einstein. Distinguishing photon amount from its energy resolves the possible ambiguity in the word einstein.
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.
CoversWavelengththe einsteinPhotochemistry
All parts of Question 1
- 1(a) Critical-point inflection5 marks
- 1(b) Boyle and inversion temperatures5 marks
- 1(c) Accuracy at high diffraction angle5 marks
- 1(d) Composition change and non-expansion work5 marks
- 1(e) Van't Hoff plots5 marks
- 1(f) Potassium sulfate activities5 marks
- 1(g) Reaction order and rate constant5 marks
- 1(h) Catalytic rate enhancement5 marks
- 1(i) Electrochemical potential of zinc ions5 marks
- 1(j) Open-circuit emf and equilibrium5 marks
- 1(k) Hermitian operators5 marks
- 1(l) Probabilities of quantum states5 marks
- 1(m) Hydrogen rotational spectra5 marks
- 1(n) Wavelength and the einstein5 marks
- 1(o) Uranyl-sensitised decomposition5 marks
- 1(p) HI photolysis yield5 marks