Q.In our daily lives, we come across three distinct modes of heat transfer: Conduction, Convection and Radiation.

Conduction (direct molecular contact), convection (bulk fluid motion), and radiation (EM waves, no medium needed) are the three heat-transfer modes; a black body is a perfect absorber/emitter of radiation.

(i) The three modes of heat transfer, with everyday examples:

1. Conduction: Heat is transferred through a material by direct molecular/atomic-level interaction, without any bulk movement of the material itself — faster-vibrating (hotter) particles pass on energy to their slower-vibrating (colder) neighbours through collisions, gradually spreading heat through the material. Example: if you leave a metal spoon standing in a cup of hot tea, the handle of the spoon (outside the tea) gradually becomes hot too, purely because heat conducts along the metal from the hot end to the cooler end. Metals are generally good conductors of heat, while materials like wood or air are poor conductors (insulators).
2. Convection: Heat is transferred through the actual BULK MOVEMENT of a fluid (liquid or gas) itself — the hotter, less-dense fluid rises, and the cooler, denser fluid sinks to take its place, setting up a circulating current that carries heat energy along with the moving fluid. Example: when water is heated in a pot on a stove, the water at the bottom (nearest the flame) heats up, becomes less dense, and rises, while cooler water from the top sinks down to replace it — this circulation, not simple conduction, is what heats the whole pot of water relatively quickly. Room heaters and monsoon land/sea breezes are also convection examples.
3. Radiation: Heat is transferred as electromagnetic waves (mostly infrared), which can travel through empty space and require NO medium at all to carry the energy. Example: we feel the warmth of sunlight on our skin even though the Sun is 150 million km away across the vacuum of space — this heat could not possibly have reached us by conduction or convection, since there is no medium (air/material) between the Sun and Earth for most of that distance; similarly, one feels the heat of a bonfire on the face even while standing a short distance away, without any physical contact or air current carrying it.

(ii) Black body radiation: …