Define temperature. Explain the working principle …

Temperature is a measure of the degree of hotness of a body.  The SI unit of temperature is kelvin (K). But temperature is also measured in celcius (°C) or fahrenheit (°F) scales. The instrument used to measure temperature is called a thermometer. 

• The thermometer is washed with water at a 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 the two bigger marks is noted. Also, the number of divisions (shown by smaller marks) between these marks is noted. For e.g. the bigger mark reads 10 and the number of division is 5, then each division reads the value equal to 10/5 = 20
• 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.