Americas
Europe
Q36P
Expert-verifiedA hydrometer is an instrument used to determine liquid density. A simple one is sketched in Figure P14.36. The bulb of a syringe is squeezed and released to let the atmosphere lift a sample of the liquid of interest into a tube containing a calibrated rod of known density. The rod, of length and average density , floats partially immersed in the liquid of density . A length of the rod protrudes above the surface of the liquid. Show that the density of the liquid is given by role="math" localid="1663764227560" .
It is proved that the density of the liquid is .
The length of the rod is .
The length of the rod not immersed in the liquid is .
The average density of the rod is .
The density of the liquid is .
The buoyant force from a liquid of density when volume of the liquid displaced is,
….. (1)
Here, is the acceleration due to gravity.
The gravitational force on a body of mass is,
….. (2)
Length of the rod immersed in the liquid is .
Let be the cross sectional area of the rod. Volume of the rod immersed in the liquid is .
This is also the volume of the liquid displaced. From equation (1), the buoyancy force on the rod directed upward is,
The total volume of the rod is and thus its mass is . Thus from equation (2), the gravitational force acting on the rod directed downward is,
At equilibrium, these two forces cancel each other. Thus
Hence it is proved.
94% of StudySmarter users get better grades.
Sign up for free