Question

What does a hydrometer consist of?
A) A cylindrical stem and a bulb weighted with mercury
B) A cylindrical stem and a bulb weighted with water
C) Only a cylindrical stem
D) Only a bulb weighted with mercury

Answer 1

Hint: The hydrometer is a device that is used to measure the density and relative density of a liquid in general. It consists of a cylindrical stem and a bulb weighted with mercury. It goes deeper into a more denser liquid and floats higher in a less dense one, thus helping to measure the density of the liquid through a calibrated scale.

Complete step by step answer:
The hydrometer is a device used to measure the characteristics of a liquid, specifically, its density and relative density or specific gravity. It consists of a bulb weighted with mercury attached to a cylindrical glass tube. The glass tube sometimes has a rubber ball at the other end to suck in the liquid whose characteristics have to be measured.
The hydrometer is dipped into the liquid to be examined. When the bulb of the hydrometer is inside the liquid, the depth up to which the bulb goes into the liquid (called the depth of floatation) is observed and then the reading is taken. The glass tube has readings on it that are calibrated accordingly to read the density and relative density of the liquid.

Hence, the correct option is A) A cylindrical stem and a bulb weighted with mercury.

Note: The hydrometer actually makes use of the Archimedes’ principle which states that when a body is partially or completely immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced by the body.
Thus, for a liquid that has a lower density, the hydrometer will sink deeper, and accordingly, a higher reading will come on the line of intersection of the surface of the liquid and the glass tube.
The Archimedes’ principle is one of the most fundamental principles in fluid statics and students are encouraged to understand it fully and to research various other instruments or daily life examples implementing it. One of these can be the sinking and rising of a submarine.