JAMB - Physics (1984 - No. 20)
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 sink. 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 needle becomes denser than water iii. kerosine reduces the surface tension of water
i only
ii only
iii only
i and ii
i and iii
Vysvetlenie
i. There is tension on the water surface.
The surface tension of water supports the needle, allowing it to float against the force of gravity.
ii. Kerosene reduces the density of water so that the needle becomes denser than water.
Kerosene does not change the density of water. It forms a separate layer on top, while the density of water remains unchanged.
iii. Kerosene reduces the surface tension of water.
Adding kerosene decreases the surface tension of water, which can eliminate the buoyant force that keeps the needle afloat.
Therefore, The accurate statements are i and iii. are correct.
The surface tension of water supports the needle, allowing it to float against the force of gravity.
ii. Kerosene reduces the density of water so that the needle becomes denser than water.
Kerosene does not change the density of water. It forms a separate layer on top, while the density of water remains unchanged.
iii. Kerosene reduces the surface tension of water.
Adding kerosene decreases the surface tension of water, which can eliminate the buoyant force that keeps the needle afloat.
Therefore, The accurate statements are i and iii. are correct.