8.4.3. Infrared waves

Infrared waves are produced by hot bodies and molecules. This band lies adjacent to the low-frequency or long-wave length end of the visible spectrum. Infrared waves are sometimes referred to as heat waves.

Infrared waves originate from hot objects or molecules. When these hot bodies emit energy, they release infrared radiation, which we can feel as heat. This section emphasizes that infrared waves aren't just a form of energy; they're linked to thermal processes occurring in our surroundings. The band of infrared waves sits next to visible light, which is the range of electromagnetic waves that our eyes can detect.

Think of a warm day in the sun. When you stand in sunlight, you feel heat on your skin; this is primarily due to infrared radiation emitted by the sun. Similarly, when you touch a heater or a hot stove, you feel the warmth as infrared waves are emitted by these objects.

This is because water molecules present in most materials readily absorb infrared waves (many other molecules, for example, CO₂, NH₃, also absorb infrared waves). After absorption, their thermal motion increases, that is, they heat up and heat their surroundings.

Infrared waves are absorbed by water molecules, leading to an increase in their kinetic energy. This increased motion translates to a rise in temperature, which is why infrared radiation is often associated with heating. Other molecules, like carbon dioxide and ammonia, also have this ability to absorb infrared, making it a crucial aspect of how heat is transferred in the environment.

When you put a pot of water on a stove, the heat from the burner transfers energy to the pot through infrared radiation. As the pot absorbs this heat, the water molecules inside begin to move rapidly—you might see steam rising as the water heats up!

Infrared lamps are used in physical therapy. Infrared radiation also plays an important role in maintaining the earth’s warmth or average temperature through the greenhouse effect.

Infrared lamps are common in physical therapy, used to relieve muscle pain by increasing blood flow through heat. Additionally, infrared radiation is critical in the greenhouse effect, where it helps maintain the earth's temperature by trapping heat in the atmosphere once the earth radiates energy back after absorbing sunlight. This process is essential for maintaining life.

Consider how greenhouses work; they let sunlight in, warming the plants and air inside. The heat radiates back outside as infrared waves, but the glass keeps some of that heat trapped inside, similar to how greenhouse gases in Earth’s atmosphere trap heat and keep it warm enough for life.

Infrared detectors are used in Earth satellites, both for military purposes and to observe growth of crops. Electronic devices (for example, semiconductor light emitting diodes) also emit infrared and are widely used in the remote switches of household electronic systems such as TV sets, video recorders and hi-fi systems.

Satellites use infrared technology for various applications, including monitoring environmental changes and military reconnaissance. Also, everyday devices like remote controls use infrared communication to transmit signals wirelessly, allowing you to change channels or adjust volume without direct contact with the device.

If you've ever used a remote control for your television, you've experienced infrared technology firsthand. When you point the remote at the TV and press a button, your remote emits a burst of infrared light that the TV detects, enabling you to change the channel from across the room!

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