Concept of Heat and Temperature

When a cold body is brought near a hot body, after some minutes, you will discover that the cold body becomes warm. This is as a result of heat transfer from the hot body to the cold body due to their temperature difference. It is important to note that heat always flows from a hot body to a cold body and not the reverse. This phenomenon can also be observed when you place a kettle of cold water on a hot stove. Heat is therefore transferred from the hot stove to the kettle raising the temperature of the water in the kettle.

• Heat is a form of energy known as thermal energy. It is the energy transferred from a hot object to a cold object due to their temperature difference.
• Temperature is simply a measure of the hotness or coldness of a body. A hot body has a higher temperature while a cold body has a lower temperature.
• Heat and temperature are scalar quantities.
• Temperature can be measured with a thermometer in degree Celsius (oC), Kelvin (K) or Fahrenheit (0F).
• According to kinetic theory, temperature is a measure of the average kinetic energy of the molecules of a body. 
• When heat is added to a body, there is an increase in the speed of it's molecules which leads to an increase in the average kinetic energy of the molecules and thus an increase in temperature.
• Also, when heat is removed from a body, there is a decrease in the speed of it's molecules resulting in a decrease in the average kinetic of the molecules and thus a decrease in temperature.

Effects of Heat

The application of heat to a body may cause several changes or effects on the body. Here are some of the effects of heat on a body:

1. Temperature change: This is the most observable effect of heat on a body. The application of heat raises the temperature of the body while the removal of heat lowers the temperature of the body.
2. Change of state of the body: The addition of heat can change the physical state of a body. The addition of heat to ice (solid) causes it to melt to water (liquid) and the continuous application of heat causes it to boil or vaporize (gas).
3. Change in pressure: The pressure and volume of a gas increases as heat is applied to it.
4. Physical expansion of the body: The application of heat causes an increase in the size of a body that is, an increase in the dimensions of the body. For example, a body can increase in length, area or volume.
5. Thermionic emission: Emission of electrons from the surface of a metal occurs when heat is applied to the metal in a process called thermionic emission.