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JAMB Physics 1983 Question 31

Question 31

Structure of Matter and Kinetic Theory

1,000 identical drops of oil of density 500 kg/m3 have a total mass of 5 × 10−4 kg. One of the drops forms a thin film of area 0.5 m2 on water. The thickness of the film is

  1. A.2 × 10−8 m
  2. B.2 × 10−9 m
  3. C.2 × 10−7 m
  4. D.3 × 10−9 m
  5. E.2.8 × 10−8 m.
Show the answer and explanation

Answer: B (2 × 10−9 m)

Explanation

One drop has mass 5 × 10−7 kg, so its volume is 5 × 10−7/500 = 10−9 m3. Thickness = volume/area = 10−9/0.5 = 2 × 10−9 m.