Radiation:
Radiation is the transfer of energy through electromagnetic waves or particles. It does not require a medium to propagate and can occur in a vacuum. In the context of heat transfer, radiation refers to the emission, transmission, and absorption of electromagnetic waves, particularly in the form of infrared radiation. It is the primary mode of heat transfer in space or between objects separated by a distance. Examples of radiation include sunlight reaching the Earth's surface, heat radiated from a fire, or the emission of thermal radiation from hot objects.
Conduction:
Conduction is the process of heat transfer through direct contact between particles of a substance or between substances in contact. In solids, heat conduction occurs as vibrating particles transfer their thermal energy to adjacent particles through molecular collisions. The kinetic energy of the particles is transferred from higher-energy regions to lower-energy regions, causing the temperature to equalize. Metals are good conductors of heat due to the mobility of their free electrons. Conduction is less efficient in liquids and gases compared to solids.
Convection:
Convection is the transfer of heat through the movement of a fluid, such as a gas or liquid. It involves the combined effects of conduction and fluid flow. Convection occurs when a heated fluid expands, becomes less dense, and rises, while cooler fluid descends to take its place. This process forms convection currents, which transfer heat from one region to another. Natural convection arises from temperature differences within the fluid, while forced convection involves external forces, such as fans or pumps, to enhance fluid motion. Convection is commonly observed in everyday situations, such as boiling water, wind currents, or the circulation of air in a room.