Thermometric substances are materials used to measure temperature. They change in physical properties like length volume or resistance with temperature variation. Common examples include mercury and alcohol in thermometers, and resistance in thermistors. These substances help convert temperature changes into measurable quantities for accurate temperature measurement in various applications.
Chapter 10 covers thermal properties of matter focusing on concepts like temperature heat and thermal expansion. It includes the behavior of solids liquids and gases with temperature changes. The chapter also discusses specific heat capacity latent heat and the laws of thermodynamics. These concepts explain how energy is transferred and transformed within substances.
A liquid thermometer is a liquid-in-glass thermometer that makes use of the expansion or contraction of a liquid to measure temperature. The most liquid used in thermometers are mercury and alcohol. The change in the rise in volume of the liquid used in the thermometer owing to the rise in the temperature is scaled on a calibrated scale to indicate temperature.
Advantages of using mercury as a thermometric substance over other liquids:
1. High Boiling Point: Mercury boils at a relatively high temperature of around 356°C. This characteristic makes it suitable for measuring high temperatures without evaporating.
2. Uniform Expansion: Mercury expands uniformly with temperature change, thus ensuring accurate readings.
3. Good Visibility: Mercury has a shiny metallic appearance, which is also easy to see, especially in the very narrow capillary tube of a thermometer.
4. Mercury is not volatile and hence non-volatile which makes it non-evaporate at room temperatures; this stability allows its longevity.
5. It possesses great thermal conductivity so gives rapid temperature variation reading
6. Non-reaction mercury. The nature is such that chemical reaction is slow or hard which makes sure the chemical interaction between substances is hard or slower due to inert.
Although these have several advantages, mercury thermometers are less commonly used today because of environmental and health concerns related to mercury toxicity.
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