Physics Form 4: Chapter 3 - Application of Archimedes Principle (Hydrometer)

• Hydrometer is used to measure the density of liquid.
• The hydrometer works on the principle that a floating object displaces a volume of liquid whose weight is equal to the buoyant force.
• Hydrometer will sink deeper in the less dense liquid but float higher in the denser liquid.

   Design of a hydrometer

Characteristic	Explanation
Lead shots are added to the base	·     To lower the centre of gravity of the hydrometer ·     So that, hydrometer can float upright in a liquid.
Thinner and longer glass tube is used	·     Will give a larger scale distance and can detect small changes in the densities.
Big bulb at the base is used.	·     So that more liquid can be displaced
For calibration, hydrometer is allowed to float in lower density and higher density liquid	·     Liquid level in lower density and higher density is marked. The space between the two marks is divided into a number of equal divisions that give density readings.