How does a hand held above a flame feel the heat?

The sensation of heat when a hand is held above a flame primarily occurs due to radiation. When a flame burns, it emits energy in the form of infrared radiation, which travels through the air. This radiant heat does not require a medium to travel and can directly affect objects in its path, such as your hand. As your hand intercepts this radiant energy, it warms up.

While convection and conduction involve heat transfer through air movement or direct contact with a heated surface, in this instance, it is the direct emission of heat from the flame that is felt without needing the air to heat up first. Therefore, when your hand is positioned above the flame, it experiences warmth primarily due to the radiant heat emitted by the flame. This illustrates how radiant heat can be sensed even without direct contact with the flame itself.