**Radiation: The Transfer of Heat as a Wave**

Heat transfer is the process of thermal energy moving from one object or substance to another. There are three modes of heat transfer: conduction, convection, and radiation. Each mode has its own unique way of transferring heat. In the case of radiation, heat is transferred as a wave.

**What is Radiation?**

Radiation is the transfer of heat through electromagnetic waves. Unlike conduction and convection, which require a medium (such as a solid, liquid, or gas) to transfer heat, radiation can occur in a vacuum or through empty space. This is because electromagnetic waves do not rely on physical contact or the movement of particles to transfer energy.

**How Does Radiation Transfer Heat?**

When an object is heated, it emits electromagnetic waves in the form of thermal radiation. These waves carry energy and can travel through space until they encounter another object. When they reach another object, the waves are absorbed, reflected, or transmitted, depending on the properties of the object.

**Absorption, Reflection, and Transmission**

When radiation waves encounter an object, several things can happen:

1. Absorption: The object absorbs the radiation waves, converting them into thermal energy. This is how objects heat up when exposed to sunlight or other sources of radiation.

2. Reflection: The object reflects the radiation waves, bouncing them off its surface. This is why reflective surfaces, such as mirrors, can redirect heat.

3. Transmission: The object allows the radiation waves to pass through it. Some materials, such as glass, are transparent to certain wavelengths of radiation and can transmit heat.

**The Role of Waves in Radiation**

Radiation is often described as the transfer of heat as a wave because the energy is carried by electromagnetic waves. These waves have specific properties, such as wavelength and frequency, which determine the type of radiation. Examples of radiation include visible light, infrared radiation, and ultraviolet radiation, all of which are forms of electromagnetic waves.

**Conclusion**

In summary, the transfer of heat as a wave occurs through radiation. Unlike conduction and convection, which require a medium, radiation can occur through empty space. When an object is heated, it emits electromagnetic waves that carry energy. These waves can be absorbed, reflected, or transmitted by other objects, resulting in the transfer of heat. Therefore, the correct answer to the question is option C: radiation.

Radiation