How a campfire and microwave are examples of heat transfer through radiation?

While both a campfire and a microwave do transfer heat through radiation, a campfire also transfers heat through conduction and convection.

Heat transfer through radiation involves the emission, transmission, and absorption of electromagnetic radiation. In the case of a campfire, heat is generated by burning wood, which produces infrared radiation. This infrared radiation is emitted in all directions, and when it comes into contact with nearby objects, it is absorbed and converted into heat. For instance, if you sit near a campfire, you feel the warmth from the infrared radiation emitted by the flames.

A microwave oven, on the other hand, primarily uses microwave radiation to heat food. Microwave radiation is a type of high-frequency electromagnetic radiation that can penetrate food and cause water molecules within the food to vibrate rapidly. This vibration generates friction and produces heat, effectively cooking or warming the food.

In a microwave, the microwaves are generated by a magnetron and then reflected by a metal cavity within the oven. As the food spins, it is exposed to the microwaves from all sides, ensuring uniform heating. Unlike a campfire, a microwave does not involve direct contact or airflow, so it does not transfer heat through conduction or convection.