Under what condition do the wet bulb temperature and dry bulb temperature become the same?

The wet bulb temperature and dry bulb temperature become the same at 100% relative humidity (RH). This occurs because, at this saturation point, the air cannot hold any more moisture, meaning the amount of moisture in the air is at its maximum.

At 100% RH, the wet bulb temperature, which reflects the cooling effect of evaporation, equals the dry bulb temperature, or the ambient air temperature, as there is no evaporation occurring. This situation indicates that the air is fully saturated with moisture, and thus, the two temperatures converge. In lower percentages of relative humidity, the two temperatures will differ because evaporation can still occur, leading to a lower wet bulb temperature.