Laboratory Thermometer

Type of Thermometer :
     (a) Clinical thermometer :
     It is a specially adapted Fahrenheit thermometer used by doctors to record the temperature of human body.

    The markings are from 95⁰ F to 110⁰ F, because the temperature of human body does not fall below 95⁰ F or rise above 110⁰ F, as in either case death occurs. Some clinical thermometers have centigrade scale, marked between 35⁰ C to 43⁰ C, the normal      temperature of human body being 37⁰ C. Before using the thermometer it should be washed with water and then jerked so that the mercury flows back into the bulb.

(b) Laboratory Thermometer :
     Different types of thermometers are used for different purposes. The maximum and minimum temperatures of the previous day, reported in weather reports, are measured by a thermometer called the maximum-minimum thermometer.The range of a               laboratory thermometer is generally from –10ºC to 110ºC. 

    In addition to the precautions needed while reading a clinical thermometer, the laboratory thermometer 

•     Should be kept upright not tilted.
•      Bulb should be surrounded from all sides by the substance of which the temperature is to be measured.  
•      Bulb should not touch the surface of the container.

    [Note:-     In clinical (Doctor’s) thermometer, Fahrenheit scale is used.
    In laboratory thermometer, Celsius scale in used.
    SI unit of temperature is kelvin (K)]

Working of Thermometer :   
    When the Thermometer bulb is in contact with a hot object, mercury column rises up through the capillary tube. The tip of the mercury column in  the capillary shows the temperature of the object.

    Clinical thermometer is used to measure the temperature of  human  body.                                      
  
    Clinical thermometers have a kink in the capillary tube. This kink prevents the mercury column to fall down as soon as the thermometer is taken out from the patient’s mouth. 

    The normal body temperature is 98.6°F (is 37°C). The range of temperature is clinical thermometer is from 94° F to 108°F (35° C to 42° C). 

    The range of a laboratory  thermometer is from –10° C to 110° C    

Ex.1     At what temperature, if any, do the following pairs of scales give the same reading : 
    (a) Celsius and Fahrenheit, 
    (b) Fahrenheit and Kelvin and 
    (c) Kelvin and Celsius ?

Ex.2    Find the value of 5ºC in ºF and K scale respectively