HEAT AND TEMPERATURE

HEAT

Heat is the form of energy which produces in us the sensation of warmth. It is responsible for the change in thermal condition of the body. Its SI unit is Joule and the practical unit of heat energy is Calorie. Heat flows from a higher temperature body to a lower temperature body when placed in contact.

1 calorie is the quantity of heat required to raise the temperature of 1g of water by 1⁰ C.

1 calorie= 4.18 joule

TEMPERATURE

Temperature is a quantity that expresses the degree of hotness or coldness of a body. The flow of heat from one body to the another body is due to their temperature difference.

The device which measures the temperature of the body is called thermometer. It was developed by Galileo who found that the gases expand on heating.

NOTE-

• The highest possible temperature achieved in laboratory is about 10⁸ K.
  
• The measurement of temperature close to 0 K, is known as cryogenics while dealing with the measurement of very high temperature, is called pyrometry.

TEMPERATURE SCALE

To measure temperature, two fixed points are taken; one of them is freezing point of water, known as ice point and other point is boiling point of water, known as steam point. The different temperature scales are listed below:

1- Celsius scale( ⁰ C ) – In this scale of temperature, the melting point of ice is taken as 0⁰ C and the boiling point of water as 100⁰ It is also known as centigrade scale. This scale was designed by Anders Celsius in 1710.

2- Fahrenheit scale( ⁰ F ) – In this scale, the melting point of ice is taken as 32⁰ F and the boiling point of water as 212⁰ This scale was designed by Gabriel Fahrenheit in 1717.

3- Kelvin scale( K ) – In this scale, the ice point and steam point are taken as 273.15 K and 373.15 K respectively. It was designed by Kelvin.

4- Reaumur scale( R ) – It is also known as “Octogesimal division“. In this scale, the ice point and steam point are taken as 0⁰ R and 80⁰ R respectively. This scale was designed by R A Reaumur in 1730.

5-  Rankine scale( Ra ) – It is an absolute scale of thermodynamic temperature named after William John Macquorn Rankine. In this scale, the ice point and steam point are taken as 460⁰ Ra and 672⁰ Ra respectively. 1⁰ Ra is equal to the 212th part of difference between two points.

RELATION BETWEEN VARIOUS TEMPERATURE SCALES

 

• Kelvin and Celsius

               K = C + 273

• Celsius and Fahrenheit

               F = 9/5(C) + 32

• Combined formula

C/5 = F- 32/9 = K-273/5 = R/4 = Ra- 460/10.6

IMPORTANT FACTS

1-The temperature at which Celsius and Fahrenheit thermometer reads same is -40⁰

2- At 574.25⁰, the Fahrenheit and Kelvin scale read the same.

3- At -25.6⁰ , the Fahrenheit and Reaumur scale read the same.

4- At 0⁰ , the Celsius and Reaumur scales read the same.

5- Normal room temperature is 27⁰ C or 80.6⁰ F or 300 K.

6- Normal temperature of human body is 37⁰ C or 98.6⁰ F or 310 K.