Thermodynamics Grade 11 combined summary

Thermodynamics ( NCERT and NEB )

 Temperature is a relative measure or indication of hotness or coldness. Hot utensils are said to have a high temperature, and ice cubes to have a low temperature. An object that has a higher temperature than another object is said to be hotter. Note that hot and cold are relative terms.

We know from experience that a glass of ice-cold water left on a table on a hot summer day eventually warms up whereas a cup of hot tea on the same table cools down. It means that when the temperature of the body, ice-cold water or hot tea in this case, and its surrounding medium are different, heat the transfer takes place between the system and the surrounding medium, until the body and the surrounding medium, are at the same temperature.

Measurement of temperature using a thermometer

A measure of temperature is obtained using a thermometer. Many physical properties of materials change sufficiently with temperature. Some such properties are used as the basis for constructing thermometers. The commonly used property is the variation of the volume of a liquid with temperature. For example, in common liquid–in–glass thermometers, mercury, alcohol, etc., are used whose volume varies linearly with temperature over a wide range.

 Thermometers are calibrated so that a numerical value may be assigned to a given temperature on an appropriate scale. For the definition of any standard scale, two fixed reference points are needed. Since all substances change dimensions with temperature, an absolute reference for expansion is not available. However, the necessary fixed points may be correlated to the physical phenomena that always occur at the same temperature.

 The ice point and the steam point of water are two convenient fixed points and are known as the freezing and boiling points, respectively. These two points are the temperatures at which pure water freezes and boils under standard pressure. The two familiar temperature scales are the Fahrenheit temperature scale and the Celsius temperature scale. The ice and steam point have values 32 °F and 212 °F, respectively, on the Fahrenheit scale and 0 °C and 100 °C on the Celsius scale.

On the Fahrenheit scale, there are 180 equal intervals between two reference points, and on the Celsius scale, there are 100.

For Practice Questions in Competitive Exams and tricks: Learn Infinite Secondary Website