# Physics

Topics: Thermodynamics, Temperature, Thermometer Pages: 5 (1455 words) Published: August 16, 2012
I. Temperature Measurement

1. A thermometric property is a physical property that changes in a known way with temperature, and can therefore be used to measure temperature. The substance used as a thermometer must have a property that varies proportionally / linearly with temperature. [ In other words: When objects are heated or cooled, their temperatures change, along with some of their properties, these properties are known as Thermometric Properties.] Two commonly used thermometric properties are resistance and length. 2. Water is generally used to determine the fixed point on a thermometer. The fixed points are freezing point (32oF/0oC) and boiling point (212oF/100oC). Upper fixed point is the temperature of pure water boiling at normal atmospheric pressure. Lower fixed point is the temperature of a mixture of pure ice and pure water at normal atmospheric pressure. Generally the upper and lower fixed points of a thermometer are determined with considering the freezing point and boiling point of water.

In Celsius thermometer, lower fixed point is 0 ºC and upper fixed point is 100 ºC, in Fahrenheit thermometer lower fixed point is determined as 32 ºF and upper fixed point as 212 ºF and finally, lower fixed point of Kelvin thermometer is 273 ºK and upper fixed point is 373 ºK. These temperatures are determined with considering the freezing point and boiling point of water. (As previously stated above). 3. Types of Thermometers

Clinical Thermometer

Clinical thermometers are used to measure the body temperature of a patient. The average temperature in a clinical thermometer is from approximately 35 degrees to 42 degrees. Advantages:
You can accurately and reliably measure peoples' body temperature with them. Also they are easy to clean, to carry around and to store. They need no power source. Disadvantages:
If it so happens that the thermometer falls and breaks, a spill of mercury in a doctor's office, school or home environment poses significant health hazards. Exposure could result in serious damage to kidneys, lungs, brain, heart and immune system.

Digital Thermometers

Digital thermometers use thermocouples or thermistors to sense the change in temperature and display the temperature on a digital display. There are a number of different types of digital thermometers therefore the temperature ranges vary. Advantages:

Digital thermometers are easy to use. When using a digital thermometer you won’t be exposed to mercury. Disadvantages:
Dead batteries are a drawback of digital thermometers. It is hard to determine how much power is left in a digital thermometer's battery, which in turn makes it difficult to predict when it will die. Because they are specialized batteries, it is hard to locate replacements. And close-to-dying batteries will provide inaccurate readings. Outdoor Thermometers

Outdoor thermometers are used to measure the temperature of the surrounding air. Temperature ranges from -58of/-50oc to 158of/ 70oC.
Low battery consumption.
High stability and accuracy.
If an object is considerably close to the outdoor thermometer it can influence the actual temperature of the surrounding air.

Thermocouple Thermometer
A thermocouple thermometer is a device for measuring temperature consisting of a pair of wires of different metals or semiconductors joined at both ends. One junction is at the temperature to be measured, the second at a fixed temperature. The electromotive force generated depends upon the temperature difference. Temperature ranges from 200oC to 2,600oC.

It is very responsive to rapidly changing temperatures due to its low thermal capacity. The low thermal capacity is due to its low mass and metals are good conductors of electricity. As the output is an electrical impulse it can be connected to a suitable electrical equipment for checking rapid or sudden temperature changes. Disadvantages:

It is extremely...