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Temperature Measurement Devices and Flow of Heat

Devices used for temperature measurement are different thermometers, thermocouples, or digital thermometers. Thermometers contain a mercury or any other fluid. Temperature is directly proportional to an expansion of mercury. As soon as the temperature increases it causes fluid to expand. Hence, the temperature can be measured by measuring the volume of fluid. There are many temperature measurement devices available such as thermocouples, resistive temperature devices (RTDs), thermistors, etc. Heat can directly be related to temperature. If the temperature of object is high, it has more energy and if the temperature is low then it has less energy. Let’s learn more about Temperature measurement and heat in detail.

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Relation of Heat with Different Parameters

Heat should not be confused with temperature but they can directly be related. Temperature is the measure of a degree of hotness or coldness.

For chemical compounds, heat depends on the speed of atoms and molecules. It is the internal energy of compound due to the virtue of molecular motion of particles contained in them. Faster is the motion of atoms and molecules, higher is the heat transfer and higher would be the temperature. Similarly, slower is the motion of atoms and molecules, lesser is the heat transfer and lower would be the temperature. Thus, heat is the result of the microscopic motion of particles.

Heat can also change the total internal energy of the system. The entry or exit of heat increases or decreases the internal energy of the body.

How Heat Flows?

Heat energy flows from one body to another body due to the difference in temperature. Heat transfers from a warmer object to the cooler object I.e. from higher temperature to lower temperature. It continues until both objects gain same temperature I.e. equilibrium is achieved.

Neither body possesses heat but a body has only internal properties like temperature and internal energy. Due to the presence of these properties, body possesses heat. Thus, energy change in the form of heat during any process will change the total internal energy of the body.

Many units for heat are devised. The standard unit I.e. SI unit to measure heat is Joules(J). The quantification of heat due to change in temperature is called calorimetry.

When a hot body comes in contact with a cold body, the temperature of the hot body falls because heat energy starts transferring from hot body to cold body. Thus, the cold body increases its temperature and hot body decreases its temperature until both come at the same temperature of equilibrium. For example-: When you hold a cup of hot tea in your hand, your hand starts getting hotter because of heat transfers from hot cup to your hand.

Units

Heat is measured in Joules or Calories and Temperature is measured in Celcius and Fahrenheit. Conversion from Celcius to Fahrenheit: °F = (9/5)°C + 32

Temperature Measurement

Temperature is the measure of heat in the body. Temperature characterizes the body as hot or cold. The SI unit used to measure the temperature in Kelvin(K). The other scales used to measure the temperature are Celsius or Fahrenheit. The instrument which is used for measuring temperature is a thermometer.

Devices for Temperature Measurement

Thermometer

A thermometer is an instrument which is used for measuring temperature of a body. The first invention to measure the temperature was by Galileo. He invented the rudimentary water thermometer in 1593. He named this device “Thermoscope”. This instrument was ineffective because water froze at low temperature.

In 1974, Gabriel Fahrenheit invented the mercury thermometer. A mercury thermometer consists of a long, narrow and uniform glass tube called the stem. The scales on which temperature is measured are marked on the stem. There is a small bulb at the end of the stem which contains mercury in it. A capillary tube is there inside glass stem in which mercury gets expanded when a thermometer comes in contact with a hot body.

Mercury is toxic and it is difficult to dispose of it when the thermometer breaks. Nowadays, digital thermometers have come into play which doesn’t contain mercury. The two commonly used thermometers are Clinical thermometers and Laboratory thermometers.

Clinical Thermometer

These thermometers are used in homes, clinics, and hospitals. These thermometers contain kink which prevents mercury to go back when it is taken out of patient’s mouth so that temperature can be noted down easily. There are two temperature scales on either side of mercury thread, one is celsius scale and other is Fahrenheit scale.

It can give temperature range from a minimum of 35°C or 94°F to the maximum of 42°C or 108°F. Fahrenheit scale is more sensitive than Celsius scale. Thus, the temperature is measured in Fahrenheit(°F).

Laboratory Thermometer

Laboratory thermometers can be used to notice the temperature in school labs or other labs for scientific research purposes. These are also used in industries to measure the temperature of solutions or instruments.

The stem, as well as bulb of laboratory thermometer, is longer when compared to the clinical thermometer. There is no kink in laboratory thermometer. It has only celsius scale. It can measure temperature from -10°C to 110°C.

Solved Example for You

Question: Mercury is widely used in clinical thermometers because:

1. Mercury is Cheap
2. Mercury is clearly visible
3. It is fashionable to use mercury
4. Mercury has a constant coefficient of expansion

Solution: Mercury is widely used in clinical thermometers because, it expands uniformly at all temperatures, hence it can help us to measure the temperature accurately. Also, it has a constant coefficient of expansion.

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