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JAMB Physics 1999 Question 13

Question 13

Gas Laws

In the J-tube above, Y and X are on the same horizontal level and 30 cm3 of air is trapped above Y when the atmospheric pressure is 75 cm Hg. Calculate the volume of air trapped above Y when 15 cm Hg is now poured into the limb above X.

Diagram for this question
  1. A.15 cm3
  2. B.25 cm3
  3. C.35 cm3
  4. D.45 cm3
Show the answer and explanation

Answer: B (25 cm3)

Explanation

The trapped air's pressure rises from 75 to 75 + 15 = 90 cm Hg. By Boyle's law 75 × 30 = 90 × V, so V = 25 cm3.