Jawaharlal Nehru Technological University Hyderabad B.Tech III Year INSTRUMENTATION AND PROCESS CONTROL Previous Question Paper (October - 2020 - R16)

A mercury-in-glass thermometer operates on the principle of thermal expansion of liquid mercury. It consists of a glass bulb connected to a narrow capillary tube with a graduated scale. As the temperature of the surrounding medium increases, the mercury inside the bulb expands. Since the bulb is the only space available for expansion, the mercury is forced up the capillary tube. The height of the mercury column in the tube is directly proportional to the temperature, which is read against the calibrated scale.

Key components include the bulb (reservoir), the stem (capillary), and the protective glass casing. The sensitivity of the instrument depends on the ratio of the bulb volume to the capillary bore diameter; a larger bulb and a finer capillary result in higher sensitivity. It is primarily used for temperatures ranging from -38°C to approximately 350°C, limited by the freezing and boiling points of mercury.

In Atomic Absorption Spectrophotometry (AAS), a light source specific to the element of interest passes through an atomized sample. The amount of light absorbed is proportional to the concentration of ground-state atoms. In contrast, Atomic Emission Spectrophotometry (AES) relies on thermal or electrical energy to excite atoms to a higher energy state. As these atoms return to their ground state, they emit light at characteristic wavelengths, the intensity of which is measured to determine concentration.