Final answer:
While Kevin and his sister are warming their hands by the fire, they are mainly experiencing heat through radiation, with convection also contributing as warm air circulates, but conduction has minimal effect as they are not touching a heat source directly.
Step-by-step explanation:
When Kevin and his sister warm their hands by the fire while camping, three methods of heat transfer are taking place: conduction, convection, and radiation. Conduction is the transfer of heat through direct contact, like when touching a warm object. However, conduction is not the primary method warming their hands since they are not in direct contact with the fire. Instead, radiation plays a significant role as heat is transferred through infrared waves, enabling them to feel warmth without direct contact. Additionally, convection occurs as the warm air surrounding the fire rises and cooler air moves in to take its place, creating a circulation of warm air. An example of conduction in daily life is when someone holds a hot cup of coffee, warming their hands. For convection, a common example is a barista steaming milk to make hot cocoa. And an everyday instance of radiation is reheating a cold cup of coffee in a microwave oven, where the microwave radiation warms the coffee.
Most of the heat transfer from a campfire to Kevin and his sister is through infrared radiation, which warms their faces and hands as they stand nearby. This is the dominant form of heat transfer they are experiencing. Although less significant in this scenario, some heat will be transferred by convection as the air heated by the fire becomes less dense and rises, drawing in cooler air from the surroundings. Conduction contributes minimally as they are not in direct physical contact with a warm surface that would conduct heat to their hands.