Question

Why does a hot cup of coffee kept open cool s after sometime

Answer 1

A cup of tea can lose heat via conduction,convection,thermal radiation,and evaporation. Lets look at each one individually

Thermal radiation is the lose of heat from solid object into the atmosphere via release of electromagnetic radiation. So the hot outer edge of the tea cup will lose its heat to the surrounding via thermal radiation

Conduction is the movement of heat along a gradient within a solid.So the inner part of the tea cup against the hot liquid will transfer that heat to the cooler outer part of the tea cup(where it will be lost by thermal radiation)

Convection is the movement of molecules of a liquid or gas within itself.So hot molecules of tea in the middle of the drink will eventually make their way to the outer part of the drink near the tea cup where they will lose their heat.

Finally evaporation is the conversion of liquid to gaseous vapour. Since vapour is in a higher energy atate than water energy required for water to evaporate.The energy in this case comes from heat of the drink.As energy lost due to evaporation drink slowly cools.