Difference Between Barometer and Thermometer

Barometer vs Thermometer

Thermometer and barometer are scientific equipment used to measure temperature and air pressure respectively. This much is perhaps known to all of us, but most of us would draw a blank if asked to explain the differences in a barometer and a thermometer. This article will explain the features of both a barometer as well as a thermometer along with their differences.

Barometer

We know the importance of air pressure and difference in pressure in deciding weather conditions. Calculation of pressure is important in forecasting cyclones and storms. Basically, air flows from areas of high pressure to areas of low pressure. High air pressure is indicative of good weather. The air pressure at the center of a storm is low compared to areas around the storm. The instrument that is used to measure air pressure is called a barometer. Toricelli invented the first barometer (using mercury) in 1643 which is the technique still being used today. The air pressure measured by barometers is also called atmospheric pressure or barometric pressure.

The schematic design of a mercury barometer contains a simple mercury filled reservoir having an inverted glass tube (around 3 feet in length) in it. The tube is closed at the top and is already filled with mercury. When this tube is placed in the reservoir, the mercury level goes down, creating vacuum at the top. This instrument works by balancing the weight of the mercury in the tube against atmospheric pressure. When the atmospheric pressure goes up, mercury level in the tube rises, and when atmospheric pressure goes down, so does the level of mercury. As atmospheric pressure (or the weight of the air above the reservoir) keeps on changing on a daily basis, the level of mercury also keeps on changing, reflecting this atmospheric pressure.

Thermometer

Thermometer is a very common device that we see as early as a small kid when we have fever and our mom tries to measure the temperature of our body with its help. Thermometer is a device that can measure the temperature inside or outside a house, inside of an oven or even your body easily. A thermometer has a small bulb at the base filled with mercury and the bulb stretches out in the form of a long tube upwards. There is a red or silver colored line calibrated on this tube and it moves up or down depending upon the temperature. Earliest thermometers used water instead of mercury, but as water freezes at zero degrees Celsius, the thermometer failed to measure temperatures below this temperature. Thermometers in US measure temperature in Fahrenheit but the scale used in the rest of the world is Celsius.

Mercury or alcohol that is used in the bulb of a thermometer grow large when heated and shrink when they are cooled. When temperature goes up, the liquid in the bulb has no place but to rise in the tube that is measured easily along the scale.