Explain why tungsten is used to make the filaments in incandescent light bulbs and why lead is used as a radiation shield in X-ray rooms. Give two reasons in total, one for each use.

Cambridge International IGCSE Chemistry (0620) — 9.2 Uses of metals · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Tungsten is used because it has a very high melting point, so it does not melt when the filament becomes extremely hot, and it has a high electrical resistance, allowing it to heat up and emit light when current flows through it.
Lead is used because it has a very high density, so it absorbs or stops X‑rays from passing through, and it does not react with or corrode in the environment, so it remains effective as a shield over a long period of time.

Examiner tips

  • Use the exact phrases ‘high melting point’ and ‘high electrical resistance’ for tungsten; use ‘high density’ and ‘does not corrode’ for lead.
  • Show the two reasons clearly, one for each metal, and keep the answer concise to match the 4 marks.

Common mistakes

  • Mixing up the properties of tungsten and lead (e.g. saying lead has a high melting point).
  • Failing to mention both required properties for each metal, giving only one reason per metal.

Mark scheme (4 marks)

  1. Tungsten has a very high melting point, so it does not melt when the filament becomes extremely hot
  2. Tungsten has a high electrical resistance, allowing it to heat up and emit light when current flows through it
  3. Lead has a very high density, so it absorbs / stops X-rays (or other ionising radiation) from passing through
  4. Lead does not react with / is not corroded by the surroundings, so it remains effective as a shield over a long period of time

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