Measuring Liquid Density: Identifying the Right Instrument

The question asks us to identify the device specifically used to measure the density of a liquid. Density is a fundamental physical property of a substance, defined as its mass per unit volume. The formula for density ($\rho$) is:

$$\rho = \frac{m}{V}$$

where $m$ is the mass and $V$ is the volume.

Let's look at the options provided and understand what each device measures:

• Anemometer: This instrument is used to measure wind speed or gas flow rate. It is commonly used in meteorology and aerodynamics.
• Bevameter: This is a device used to measure the mechanical properties of soil, specifically its strength and deformation characteristics under load. It is relevant in terramechanics, often associated with vehicle mobility over soil.
• Eudiometer: This is a graduated glass tube used to measure the change in volume of a gas mixture following a physical or chemical reaction. It is typically used in chemical analysis, particularly in gas analysis.
• Pycnometer: Also known as a specific gravity bottle, a pycnometer is a flask with a precisely defined volume used to determine the density of liquids or solids. It works by measuring the mass of the liquid that fills the pycnometer's known volume.

To measure the density of a liquid using a pycnometer, the following steps are typically involved:

1. Weigh the clean, dry pycnometer.
2. Fill the pycnometer completely with the liquid whose density is to be measured and weigh it again.
3. Determine the mass of the liquid by subtracting the mass of the empty pycnometer.
4. Since the volume of the pycnometer is known (usually calibrated using a reference liquid like water), the density of the liquid can be calculated using the mass and the known volume.

Based on the functions of the devices listed, the pycnometer is the instrument specifically designed for accurately measuring the density of a liquid.

Revision Table: Understanding Measuring Devices

Additional Information on Density Measurement

While a pycnometer is a precise tool for measuring liquid density, other methods and related concepts exist:

• Hydrometer: A hydrometer is another device used to measure the density or specific gravity of liquids. It works based on Archimedes' principle; it floats higher in denser liquids and lower in less dense liquids.
• Densitometer: This is a broader term for any instrument that measures density. It can include various types, from simple hydrometers to more sophisticated digital densimeters.
• Specific Gravity: Specific gravity (or relative density) is the ratio of the density of a substance to the density of a reference substance (usually water for liquids). It is a dimensionless quantity. A pycnometer can also be used to determine specific gravity.
• Archimedes' Principle: This principle states that the upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid that the body displaces. This principle is the basis for instruments like hydrometers and is also relevant when considering buoyancy methods for density measurement.

Understanding the specific application helps in selecting the appropriate device for density measurement. For accurate laboratory measurement of liquid density, a pycnometer is a standard instrument.