How Thermometers Work?
Thu, Mar 11, 2010
Alcohol and mercury thermometers;
The bulb thermometer is the common glass thermometer , and Inside a thermometer is a liquid, such as alcohol or mercury.The mercury thermometer was originally invented by the German physicist Daniel Gabriel Fahrenheit and basically consists of a volume of mercury being trapped inside a glass envelope. Most of the mercury mass is located in the so-called bulb (both alcohol and mercury thermometers are known as bulb thermometers) that connects to a much narrower tube inside which the mercury can expand.
Bulb thermometers rely on the simple principle that a liquid changes its volume relative to its temperature. When the liquid comes into contact with something warm, it’s particles gain energy, causing the substance to expand and take up more room within the thin tube. When the liquid comes in contact with something cold, that cusses the liquid to squish together.
scale?
Making a Celsius (centigrade) thermometer is easy, because it’s based on the temperatures of ice and boiling water. These are called the two fixed points. Ice has a temperature close to 0°C while water boils at 100°C. If we dip our thermometer in some ice, we can observe where the mercury level comes to and mark the lowest point on our scale, which will be roughly 0°C. Similarly, if we dip the thermometer in boiling water, we can wait for the mercury to rise up and then make a mark equivalent to 100°C.
Electronic thermometers ;
Electronic thermometers work in an different way to mechanical ones that use lines of mercury or spinning pointers. They’re based on the idea that the resistance of a piece of metal (the ease with which electricity flows through it) changes as the temperature changes. As metals get hotter, atoms vibrate more inside them, it’s harder for electricity to flow, and the resistance increases. Similarly, as metals cool down, the electrons move more freely and the resistance goes down. (At temperatures close to absolute zero, the lowest theoretically possible temperature of −273.15°C or −459.67°F, resistance disappears entirely in a phenomenon called superconductivity.) 
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