How does Infrared Radiation work? Discovery, Detection, Properties and Facts about Infrared
In this hub, I have discussed in detail about Infrared (IR) radiation, discovery of Infrared radiation, how IR radiation works, its detection and some interesting facts about IR radiation.
Before going into the working of infrared radiation, let us briefly look at what infrared radiation is and how it is produced.
If you like to read about the many uses and applications of infrared radiation and the hazards of infrared radiation, please follow the link below.
The electromagnetic spectrum consists of visible light, radio waves, x-rays, gamma rays, microwaves, infrared rays and ultraviolet rays. The differences between these radiations are their wavelengths or frequencies. The infrared radiation is part of the electromagnetic spectrum and lies above the visible red region of the spectrum and it is invisible radiation. Its wavelength is between (longer than visible red) the visible red light and the (shorter than microwaves) microwaves of the electromagnetic spectrum, that is 0.74 micrometers (µm) to 1 millimeter (mm).
Sir William Herschel: infrared radiation and its applications
Discovery of Infrared Radiation:
Infrared radiation was discovered in 1800 by an English Astronomer called William Herschel. While Herschel was measuring the temperature of Sunlight that was split into a spectrum, he found that higher temperatures were felt beyond the visible red region of the spectrum, which he measured using a thermometer. So he confirmed that some invisible radiation existed beyond the red region of the spectrum that was responsible for this heat and he named it initially as “Calorific Rays.” Calorific means “Heat generating.” These were called infrared (infra means below) rays in the late 19th century. Even though the wavelength of infrared radiation is higher than the visible red light, the frequency is lower than red, hence the name infrared.
The formula below will explain this clearly.
Speed (velocity) of light = Wavelength x Frequency
Speed of Light is a constant which is 299792.458 km per second in vacuum. In order for the speed of light to remain a constant, when wavelength increases, the frequency has to decrease and vice versa.
So cross multiplying the above equation, we get
Speed of light (C) = Frequency (f) x Wavelength (λ)
C = fλ
Where is infrared radiation found?
Infrared red waves are emitted by all warm objects. They also heat up the objects on which they fall. When they fall on any substances, the molecules in the substances absorb this energy and get excited and as a result of this, the substance gets heated. A very good example is the earth. Earth gets heated up, due to the infrared radiation falling on it from the Sun.
How does Infrared radiation work?
Infrared radiation is heat radiated by an object. When an object gets heated, it gains energy as a result of which the atoms and molecules move or vibrate and radiate infrared which is heat. Objects that are not hot enough to radiate visible light will radiate infrared. When infrared waves touch a surface or fall on any substances / objects, heat energy is released. This heat energy is not dependant on the temperature of the surroundings.
Examples of infrared radiation are, heat from the Sun, heat from fire, heat from radiator, etc.
In order to explain how infrared radiation works, the best example is the heating and cooling of the earth. During the day time when the Sun shines, the earth gets warm due to infrared radiation falling on it. In the night, after the Sun has gone down, the earth emits infrared radiation
Wonders of Physics: Infrared Radiation
For example, on an extremely cold but sunny day, skiers, mountain climbers and people involved in similar activities or winter sports do not feel the cold because, they are heated up by the infrared radiation from the Sun and the infrared radiation reflected by the stones and other material in the environment. Heat energy is also emitted or released regardless of the surrounding temperature, when infrared rays fall on any surfaces or objects.
So feeling warm or cold has got nothing to do with the temperature of the surrounding air, but it is to do with absorption of infrared radiation (warming up) or emission / releasing of infrared radiation (cooling down when temperature around us is colder than our body temperature).
Infrared rays travel through air and vacuum and they do not need a medium to travel through. They heat up any objects on which they fall and produce heat. For example surface of the earth, walls of the house, human body, etc.
The energy from the Sun that reaches the earth has a higher percentage of infrared radiation.
Different regions of the infrared:
The infrared radiation is spread across a band (spectrum) of wavelengths (0.75 micrometer to 1000 micrometers) and hence it is divided into smaller sections. Sensors are very sensitive and do not detect all of these wavelengths and they will be built to sense a particular / small band of wavelengths. So infrared radiation of each region has different use or application. The different divisions of the infrared region are as follows and this is the most common subdivision scheme.
- Near-infrared (NIR , IR-A) – This is the region near to the visible red region. This is used in fibre optic communication and night vision devices. It is also used in remote controls, astronomy, remote monitoring, material science, medical field and agriculture. The wavelength range is from 0.75 to 1.4 micrometers.
- Short wavelength infrared (SWIR, IR-B) – This is used for long distance telecommunications and the wavelength range is from 1.4 to 3 micrometers. It is also used in SWIR cameras, night vision goggles that play a major role for military purposes
- Mid wavelength infrared (MWIR, IR-C) – This is used in guided missile technology, infrared spectroscopy, communication, chemical industry, and the wavelength range is 3 to 8 micrometers. It also finds application in astronomy.
- Long wavelength infrared (LWIR, IR-C) – This is the thermal infrared region and is used to detect thermal emissions that require no illumination from other sources (thermal imaging). This finds extensive application in astronomical telescopes and optical fibre communication. The wavelength range of this division is 8 to 15 micrometers
- Far infrared (FIR) – These are used in infrared lasers, astronomy, infrared saunas and extensively used in the medical field and the wavelength range is 15 to 1000 micrometers. It also strengthens the immune system.
The other schemes are:
Detection of Infrared radiation:
Infrared radiation can be detected by infrared detectors that react to infrared radiation. One can feel infrared radiation by its property of heating up the skin and other objects. Infrared imaging cameras are a good example for recording infrared images. There are some electronic devices that can detect infrared radiation and they have to be maintained at a lower temperature in order to avoid heat from the device interfering with the detection of infrared.
Some devices that are used to detect infrared radiation are:
- Thermocouple detectors, Bolometers - Heat sensitive devices that react to the presence of IR radiation
- Photovoltaic cells, photoconductors - made of semicinductor materials. The electrical conductivity of these materials increase when exposed to infrared radiation thereby helping with the detection of IR radiation
Infrared: More Than Your Eyes Can See
Properties of Infrared radiation:
- Infrared radiation can travel in vacuum at the speed of light.
- Infrared radiation can travel through thick fog, thick smoke, dust and some other materials through which visible light cannot travel.
- Infrared radiation heats up objects on which they fall
- Infrared rays can be absorbed or reflected depending on the nature of the substance they fall on.
- Infrared has wavelength longer than visible light and shorter than microwaves
Facts about infrared radiation:
- Infrared radiation does not involve particles.
- Infrared radiation is emitted by all objects above zero degrees Kelvin (zero degrees kelvin is absolute zero which is -273.15 degrees Celsius or -459.67 degrees Fahrenheit and is the temperature below which all atomic and molecular motion stops). So even ice that we consider as a cold object emits infrared radiation.
- The higher the temperature of any object, the more infrared radiation it will emit.
- Infrared radiation cannot be seen but can be felt as heat.
- The infrared region close to visible light (near infrared region) is not warm and this is used in remote controls and for data transmission between a computer's peripheral devices.
- Human body naturally produces infrared within the tissues which help with healing and cell repair
To read more about the uses, applications and hazards of infrared, please follow the link below.
I hope this hub has been useful and interesting. Please feel free to share your thoughts, experiences and ideas on this subject. I would like to hear from you.
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Thank you for reading.