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UPSC Combined Geo-Scientist

Chemist

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

Mains Paper III covers analytical and organic chemistry.

UPSC Combined Geo-Scientist, Mains · 2021 · Mains Paper III

Q1(g). Hollow-cathode lamp: function and working

Question

Mention the function of Hollow Cathode Lamp (HCL). How does it function?

Answer in brief

It is the line source of AAS, emitting the sharp resonance lines of the analyte: a discharge in low-pressure Ne or Ar gives ions that sputter cathode metal atoms, which are excited and emit.

Key points

  • Function: emits the resonance lines of the analyte at exactly the wavelength its atoms absorb, narrower than the absorption line.
  • Construction: sealed tube with Ne or Ar at 1–5 torr; hollow cathode of the analyte metal; W or Zr anode.
  • Working: gas ionised; ions sputter metal atoms from the cathode; atoms excited by collisions; M* → M + hν.
  • Low temperature and pressure in the lamp: less Doppler and collisional broadening, so a narrow line.

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.

Model answer to Q1(g), 2021 Mains Paper III: solution pages 7 and 8
Solution pages 7 and 8 of 39
Read the whole 2021 solution2021 question paper

Topic notes: spectroscopic instruments (Beer–Lambert law, UV–vis and IR instruments, Job's method, AAS and flame emission), with every Civil Services, IFoS and Geo-Scientist PYQ →

Covershollow cathode lampatomic absorption spectroscopyline sourcesputtering

All parts of Question 1