Measurement of heat and Temperature

 

Measurement of Heat : Heat or the thermal energy is defined as energy that is transferred between a system and it's environment because of the temperature difference between them. Before scientists arrived at a correct understanding of heat ,the units in which heat was measured had already been developed. One of the most widely used is the calorie ( cal) ,defined as the heat required to raise the temperature of lg of water from 14.5°C to 15.5°C. a related unit is the kcal. 1 kcal = 10/3 cal. The unit if heat in the British engineering system is the British thermal unit ( BTU) ,defined as the heat required raising the temperature of 1 Ib of water from 63°F to 64°F.  Because heat is now recognized as energy being transferred ,scientists are using increasingly SI unit of energy, the joule (J) ,for the quantities of heat . 1 cal= 4.186 J.                                                          Measurement of Temperature: The common thermometer used to measure temperature is essentially a sealed glass tube containing a liquid such as mercury or colored alcohol, The principle involved in the functioning of a thermometer is that fluids generally expand when heated and contract when cooled. ( Solids expand and contract too but the glass, in a thermometer does not expand enough to affect the reading materially ). The Hollow inside the thermometer ,the bore, is very narrow ,in some thermometers it is finer then a human hair ,thus , a small change in temperature causes enough in temperature causes enough expansion or contraction in the liquid to force it a noticeable distance up or down the bore, the tube is calibrated that is marked in degrees so the expansion or contraction of the fluid can be measured in exact units.                                                               Scales: there are two common temperatures in use ,the fahrenheit and the Celsius scale, the fahrenheit thermometer is so calibrated that it registers 32 point of ice and 212 degrees at the boiling point water, these measurements are written 32°F and 212°F respectively, there are 180° between the melting point of ice and the boiling point of water ,the scale may be extended below and above these points. Incidentally, the zero of the fahrenheit the thermometer does not mean , no degrees ,this zero point was somewhat arbitrarily selected by its originator ,Fahrenheit, who on mixing some salt and ice, achieved a low temperature that he decided are needed to determine the calibration,so a second point of 100 was selected with fahrenheit believed was the temperature of the human body .on the Celsius scale ,zero marks the melting point of ice and 100 the boiling point of water ,these measurements are written 0°C and 100°C respectively. A third scale,one sometimes useful to scientists ,is the Kelvin scale, also called the absolute temperature scale, which begins with absolute zero but use degrees that have the same size as Celsius degrees ,To convert from Celsius to Kelvin and 273 to the Celsius reading ,some signification temperatures ( approximations) are shown in the table above,

A  Thermometer.                                                    Thermometer come in different shapes and size for different purpose. The clinical thermometer has a very narrow bore ,so that a different of 1/10 degree is easily read. It is calibrated to read only from92°F to 110° F.Heat forces the mercury out of the bulb and up the bore , but a constriction in the bore keeps the mercury up in the stem when the thermometer is removed from the patient even though the surrounding temperature is lower ,in this way the thermometer registers the highest point to which the mercury back into the bulb.