1. What are infrared waves?
Infrared (IR) waves lie between microwaves and visible light in the electromagnetic spectrum. They are mainly known for carrying heat. When objects are warm, they emit infrared radiation naturally.
Although we cannot see infrared with our eyes, we can feel it as warmth when standing near a heater or under sunlight.
1.1. General characteristics
- Wavelength: around 1 millimeter to 700 nanometers
- Frequency: \(10^{12}\) Hz to \(4 \times 10^{14}\) Hz
- Experienced mainly as heat radiation
- Emitted by all warm objects
1.2. Where infrared fits in the spectrum
Infrared waves lie just below visible red light. As wavelength decreases and frequency increases, infrared gradually transitions into visible light.
2. How infrared waves are produced
Any object with a temperature above absolute zero emits infrared radiation. Hotter objects emit more infrared and at shorter wavelengths.
2.1. Thermal emission
Atoms and molecules inside warm objects vibrate. This vibration leads to emission of electromagnetic radiation, much of which lies in the infrared region.
2.2. Electronic transitions
Certain atoms and molecules emit infrared when electrons change energy levels or when molecules rotate and vibrate internally.
2.3. Artificial sources
- Infrared LEDs
- Heating lamps
- Laser diodes
- Remote-control transmitters
3. Interaction of infrared waves with matter
Infrared interacts strongly with molecules, especially those found in living tissues, food, and atmosphere. Much of this interaction produces heat.
3.1. Absorption by molecules
Molecules such as water, carbon dioxide, and organic compounds absorb infrared strongly. This absorption causes molecular vibration and heating.
3.2. Infrared in the atmosphere
Water vapor and carbon dioxide absorb infrared, which plays a major role in greenhouse effects and Earth's warming.
3.3. Penetration and reflection
Infrared can penetrate through smoke and some cloth materials but reflects strongly from shiny surfaces and metals.
4. Uses of infrared waves
Infrared technology is used widely in everyday life, medicine, communication, and science because of its heating ability and easy detection.
4.1. Remote controls
TV remotes and other remote-control devices use infrared LEDs to send coded signals. The receiver detects these signals and converts them into commands.
4.2. Thermal imaging
Thermal cameras detect infrared radiation emitted by warm objects. These images are used in night vision, search and rescue, wildlife studies, and building inspections.
4.3. Medical and therapeutic applications
- Infrared therapy for muscle relaxation
- Heat lamps for pain relief
- IR-based sensors for measuring body temperature
4.4. Communication systems
Infrared waves are used in short-range communication like IR blasters, sensors, and some wireless data-transfer systems.
4.5. Industrial applications
- Drying and heating processes
- Infrared spectroscopy for chemical analysis
- Quality control in manufacturing
5. Infrared detection
Infrared detectors convert incoming IR radiation into electrical signals. These detectors make thermal imaging and remote sensing possible.
5.1. Common detectors
- Photodiodes
- Bolometers
- Pyroelectric sensors
- Thermopile sensors
5.2. Where infrared detection is used
- Night-vision goggles
- Thermal cameras
- Motion sensors
- Smartphone sensors
6. Example of infrared in daily life
When you stand near a campfire, you feel warmth even when the air around you is cool. This warmth is due to infrared radiation emitted by the fire. Your skin absorbs this infrared energy and warms up. This is a simple demonstration of how IR radiation carries and transfers heat.