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JAMB Physics 1984 Question 24

Question 24

Structure of Matter and Kinetic Theory

A small steel needle is carefully floated on water in a beaker. When a few drops of kerosine are introduced into the water the needle sinks. Which of the following statements correctly explain(s) the observation? I. There is tension on the water surface II. Kerosine reduces the density of water so that the needle becomes denser than water III. Kerosine reduces the surface tension of water.

  1. A.I only
  2. B.II only
  3. C.III only
  4. D.I and II
  5. E.I and III.
Show the answer and explanation

Answer: E (I and III.)

Explanation

The needle is held up by the surface tension of the water surface. Kerosine lowers the surface tension, so the surface film can no longer support it.