Temperature and heat are two words which often confuse people. Suppose mistakenly you touched a hot object. How will you explain it to someone about the hotness of that object? What is the measure or basis for the hotness? Yes, it is the temperature. Heat is a form of energy; its unit is Joules. Temperature is the measure of that heat i.e. more the heat, more is the temperature. Thermometer is the device used to measure this temperature. Let’s learn different types of thermometers in details.
Temperature & Thermometer:
By definition, temperature is the measurable extent of hotness or coldness. It is a mathematical representation of heat. Thermometer (thermos: hot; metron: measure) is the universal instrument used to measure temperature. Different units of temperature are Celsius (˚C), Kelvin (K) and Fahrenheit (˚F). There are different types of thermometers like the one which is used to measure body temperature can’t be used to measure the boiling point or freezing point during experiments. Here, we will discuss the two types of thermometers, namely, clinical thermometer and laboratory thermometer.
Clinical thermometers are meant for clinical purposes. It is developed for measuring the human body temperature. It is a long narrow glass tube with a bulb containing mercury at the end. The normal human body temperature is 37˚C; it can fluctuate between the ranges 35˚C to 42˚C. Hence, the clinical thermometers have the range 35˚C to 42˚C. The level of mercury tells our body temperature in ˚C. Since mercury is toxic element mercury thermometers has been replaced by digital thermometers nowadays.
Note: Clinical thermometers must be sterilized before use for the safe and clean checkup.
Reading a Thermometer:
- The thermometer is washed with water at normal temperature.
- It is given a few jerks. We notice that the jerks bring the level of mercury down. We make sure that it falls below the 37⁰C mark or the 98⁰F mark, the normal human body temperature.
- The thermometer is then kept under the tongue or under the arms in order to get the reading on the thermometer.
- The thermometer is then held close to the eye as shown in figure 3 in order to see the correct reading.
- The temperature difference indicated between two bigger marks is noted. Also, the number of division (shown by smaller marks) between these marks is noted. For e.g. the bigger mark reads 10o and the number of division is 5, then each division reads the value equal to 10/5 = 2o
- We note the value of the bigger mark that the mercury thread has crossed (which is 98 in the Fig.4 Example 1). Then the number of the division of the mercury thread has crossed is noted (3 in this case). Now, this value is multiplied by the value of one division (which is 0.2 in this case). Hence, the temperature reading is 98 + (3×2) = 98.6.
Since clinical thermometers can’t be used to measure temperature other than the human body, we need a special type of thermometers for other purposes. A laboratory thermometer is used for measuring temperatures other than the human body temperature. Its range is -10˚C to 110˚C. Laboratory thermometers are designed for lab purposes such as checking boiling point, freezing point, or temperature of other substances. You can use a laboratory thermometer for checking the temperature of a solvent but not a clinical one.
Weather reporters use maximum-minimum thermometers for measuring maximum and minimum temperatures of a place.
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