Anomalous expansion of water:

Anomalous expansion of water: Almost every liquid expands with the increase in temperature. But when temperature of water is increased from 0˚C to 4˚ C its volume decreases. If the temperature is increased above 4˚C, its volume starts increasing. Clearly, density of water is maximum at 4˚C.

Transmission of Head: The transfer of heat from one place to other place is called transmission of heat. There are three modes of heat transfer- (i) conduction, (ii) convection and (iii) radiation.

Conduction: In this process, heat is transferred from one place to other place by the successive vibrations of the particles of the medium without bodily movement of the particles of the medium. In solids, heat transfer takes place by conduction.

Convection: In this process, heat is transferred by the actual movement of particles of the movement from one place to other place. Due to movement of particles, a current of particles set up which is called convection current.

 In liquids and gases, heat transfer takes place by convection.

Earth’s atmosphere is heated by convection.

Radiation: in this method transfer of heat takes place with the speed of light without affecting the intervening medium.

Newton’s law of cooling: The rate of loss of heat by a body is directly proportional to the difference in temperature between the body and the surrounding.

Kirchhoff’s law: According to Kirchhoff’s law, the ratio of emissive power to absorptive power is same for all surfaces at the same temperature and is equal to emissive power of black body at that temperature.

Kirchhoff’s law signifies that good absorbers are good emitter.

If a shining metal ball with some black spot on its surface is heated to a high temperature and seen in dark, the shining ball becomes dull but the black spots shines brilliantly because black spot absorbs radiation during heating and emit in dark.