6.3.1 Emission and Absorption of Infrared Radiation

In this lesson, we will explore the concepts of emission and absorption of infrared radiation. We will learn how all objects, regardless of temperature, emit and absorb infrared radiation.

Infrared Radiation and Body Temperature

All objects, regardless of their temperature, emit and absorb infrared radiation. The amount of infrared radiation emitted by a body increases with an increase in temperature. Hotter bodies radiate more infrared radiation in a given time compared to cooler bodies.

Perfect Black Body

A perfect black body is an idealised object that absorbs all of the incident radiation falling on it.

• Absorption: A black body absorbs all wavelengths of radiation incident upon it and does not reflect or transmit any radiation.
• Emission: A good absorber is also a good emitter, which means a perfect black body would be the best possible emitter of radiation.

Emission and Absorption

• Emission: When an object emits infrared radiation, it is releasing energy in the form of electromagnetic waves. The hotter the object, the more infrared radiation it emits.
• Absorption: Objects can also absorb infrared radiation when it is incident upon them. The amount of radiation absorbed depends on the object's properties and its ability to interact with the radiation.

Applications of Infrared Radiation

Infrared radiation has various practical applications in different fields, including:

• Thermal Imaging: Infrared cameras capture the emitted infrared radiation to create images that reveal temperature variations.
• Heating and Cooking: Infrared heaters and cookers utilise the absorption of infrared radiation by objects to generate heat.
• Remote Sensing: Infrared sensors are used in remote sensing applications to gather information about Earth's surface and atmosphere.

Conclusion

Infrared radiation is emitted and absorbed by all objects, regardless of their temperature. The emission of infrared radiation increases with the temperature of the body, with hotter objects emitting more radiation. A perfect black body is an idealised object that absorbs all radiation incident upon it and would be the best possible emitter. The applications of infrared radiation in various fields highlight its significance in thermal imaging, heating, cooking, and remote sensing.