Question

A hydrometer floats with half of its stem outside the water surface. It is now placed in alcohol $\left(R.D.=0.8\right)$. The hydrometer floats:

• A. with stem at the same position
• B. with more stem inside the alcohol
• C. with more stem outside alcohol
• D. in tilted position

Answer 1

The correct option is B

with more stem inside the alcohol

The explanation for the correct option:

Option B: with more stem inside the alcohol:

1. Hydrometer measures the relative density of liquids by reading the markings on the hydrometer at the point where the stem is crossing the liquid surface.
2. According to Archimedes' principle, the upthrust experienced by an object immersed in a liquid is equal to the mass of fluid displaced by the object.
3. As the relative density of alcohol is less than one, alcohol is less dense than water.
4. Thus, more amount of alcohol must displace to support the hydrometer.
5. Thus, more part of the hydrometer should be dipped in alcohol.

Thus, the hydrometer floats with more stem inside the alcohol.

Hence, the correct answer is Option B.