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Infrared radiation (IR radiation) also known as infrared rays is electromagnetic radiation having a wavelength ranging from 700 nm to 1 mm. The human eye cannot see it, but detect it as heat.
- The frequency of IR rays ranges from 1011 Hz to 1014 Hz.
- The wavelength of infrared rays is greater than those of visible light but shorter than radio waves.
- The frequency of infrared waves is higher than microwaves but lower than those of visible light.
- It is produced by hot bodies i.e. vibrations of atoms and molecules. Hence, also known as Heat waves.
- It is detected by thermopiles, bolometers, and infrared photographic film.
- Infrared waves are responsible for keeping the average temperature through the greenhouse effect.
| Table of Content |
Key Terms: Electromagnetic spectrum, electric charges, Infrared radiation, wavelength, electric field, magnetic field, electromagnetic radiation, visible light, frequency, energy.
Electromagnetic Waves Definition
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Electromagnetic waves are the flow of energy in which both electrical and magnetic fields change at the same time. They are produced by accelerating and oscillating charged particles. They travel in free space with the speed of light and do not require any material medium for their propagation.
- Everything around us such as the sun, earth, and other bodies is known to radiate electromagnetic energy of varying wavelengths.
- The electromagnetic energy moves through space at the velocity of visible light which is in the form of sinusoidal waves.
- The orderly distribution of electromagnetic radiation according to its frequency or wavelength is called the Electromagnetic spectrum.
- Maxwell predicted the existence of electromagnetic waves and experimentally discovered by Hertz.
- The electromagnetic spectrum ranges from shorter to longer wavelengths.
- The electromagnetic spectrum includes all types of radiation, ranging from the radio waves used for communication to X-rays used at hospitals.
The above image shows the various radiations within the electromagnetic spectrum.
- The rays on the right side of the spectrum have a lower wavelength whereas the rays on the left side have higher wavelengths.
- The radiations having longer wavelengths such as radio, microwave, and infrared are considered to be less harmful.
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Radiations having lower wavelengths such as gamma, X-rays, and ultraviolet are considered to be very dangerous.
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Infrared Radiation Definition
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Infrared Radiation is one of the electromagnetic radiations of an electromagnetic spectrum. It is also known as infrared light which is not visible to the naked eye due to its longer wavelength. Instead, they can only be felt in the form of heat.
- The wavelength of Infrared radiation ranges between 700 nm and 1 mm which is a longer wavelength as compared to visible light
- Its frequency range from 1011 Hz to 1014 Hz.
- Infrared ray was discovered by British astronomer Sir William Herschel in 1800.
- Infrared radiation provides luminous energy and it functions both as a wave and like its quantum particle, called a photon.
- Infrared Radiation is generally divided into 5 categories according to wavelength and frequency.
- This comprises near-wavelength, short-wavelength, mid-wavelength, long-wavelength, and far-Infrared.
Infrared Radiation
Characteristics of Infrared Radiation
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The Infrared radiations consist of various characteristics some of which are mentioned below:
- The wavelength of IR ranges from 700 nm to 1 mm.
- Its frequency range from 1011 Hz to 1014 Hz.
- Infrared radiation is a Transverse wave
- They share some characteristics with visible light, namely infrared light can be focused, reflected, and polarized.
- It is produced by vibrations of atoms and molecules.
- It consists of heat-inducing properties.
- These waves are readily absorbed by water, CO2, NH3, etc.
- The wavelength of Near-Infrared rays is close to that of visible light. They can be used in the TV remote, photography, etc.
- The Far-Infrared rays are more thermal as compared to near-infrared wavelengths.
Properties of Infrared Radiation
The list of unique properties possessed by infrared radiation has been mentioned below:
- Electronic Origin
It is assumed that all EM radiation, including infrared light, originates from the point where there is some alteration in the movement of electrons.
- Transverse waves
Other electromagnetic radiations including infrared consist of transverse waves. When any displacement or waviness of the wave at right angles to the direction in which the energy of the wave is moving, then the wave is called a transverse wave.
- Wavelength
The infrared waves generally have unique wavelengths which are measured in microns. The shortest wavelength of infrared is assumed to be 0.7 microns whereas the longest wavelength is assumed to be about 350 microns.
- Speed
Just like other electromagnetic radiation, infrared light moves at the rate of 299,792,458 meters per second as per “Serway’s College Physics”.
- Particles
Infrared light also exhibits properties that are the characteristics of particles such as wave properties. According to “The New Quantum Universe” infrared light can exist both as a wave as well as a particle at the same time.
- Absorption and reflection
Based on the nature of the substance that it strikes, infrared radiation can be absorbed or reflected in a way similar to the radiation of visible light. For instance, water vapor, CO2, and ozone absorb infrared radiation effectively.
- Thermal properties
The transfer of energy is termed heat. One of the mediums by which energy transfer is affected is infrared light. A huge amount of energy that reaches the earth from the sun is in the form of infrared radiation.
- Refraction
Infrared light exhibits the property of refraction which determines that the direction in which the light is moving suffers a slight change in the direction when the radiation passes from a medium such as outer space, into another medium that has a different density, like Earth’s atmosphere.
- Interference
This property states that if two infrared rays are having the same wavelength to meet each other, then they will interfere with one another. Based on how they meet, they will reinforce or cancel each other at changing levels.
Wavelength of Infrared Radiation
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The categories for wavelength under the specific spectral range can be described as:
- 1µm to 3µm: known as Short Wave Infrared radiation
- 3µm to 5µm: known as Middle Wave Infrared Radiation
- 8µm to 14µm: known as Long Wave Infrared Radiation
Characteristics of Regions of Infrared
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The Infrared radiations are categorized into various regions the characteristics of the regions have been mentioned in the table below:
| Near-infrared ray | Its wavelength ranges from 0.75 to 1.4 micrometers. The application includes material science fiber optic communication and the medical field, etc. |
| Short-wavelength infrared ray | Its wavelength ranges from 1.4 to 3 micrometers. The application includes military purposes |
| Medium infrared ray | Its wavelength ranges from 3 to 8 micrometers. It is used in the fields of the chemical industry and astronomy |
| Long-wavelength infrared ray | Its wavelength ranges from 8 to 15 micrometers. It can be used in astronomical telescopes and optical fiber Communications, etc. |
| Far infrared ray | Its wavelength ranges from 15 to 1000 micrometers. It is mainly used in the treatment of cancer therapy |
Application of Infrared Radiation
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Various uses of Infrared radiation are:
- Heat source:
- Medical uses: Infrared radiation can be used for Physiotherapy as it is considered as one of the safest methods. It can also be used for the treatment of high blood pressure which has an effect on health causing chronic problems and rheumatoid arthritis.
- Manufacturing industries: Industries which deal with manufacturing processes of plastic, welding of plastics, curing of coatings, etc. make use of infrared heaters.
- Cosmetology Application:
Infrared radiation is generally used for cosmetic applications in order to treat skin injury, smoothen wrinkles, reduce the prevalence of dandruff blackheads, etc the reason is that infrared radiation can penetrate for three to four micrometers within the skin. Its radiation also helps in warming the skin as a result of which in improvement and birth blood circulation can be seen with a continuous supply of Oxygen and other nutrients to the skin.
- Astronomy:
Astronomers make use of infrared waves while using optical devices such as solid-state digital detectors, mirrors, and lenses in order to study objects from space. The images collected from these devices can be understood with the help of an infrared telescope.
- Massage therapy:
During massage therapies infrared rays are used in order to warm up the skin which helps in the relaxation of the muscles. It is also preferred because they can penetrate through the skin and are not harmful.
- Infrared photography:
During infrared photography, infrared filters are generally used for capturing the images. The images are acquired for objects that are positioned in a near-infrared spectrum. In most cases the digital cameras used infrared blockers which helps in making the near-infrared a pure purple-white color in the final image.
Things to Remember
- Infrared radiation is electromagnetic radiation having a wavelength ranging from 700 nm to 1 mm.
- It is produced by vibrations of atoms and molecules.
- Infrared radiation was first discovered by Sir Frederick William Herschel in the year 1800.
- Electromagnetic waves are the flow of energy in which both electrical and magnetic fields change at the same time.
- Ir waves comprise near-wavelength, short-wavelength, mid-wavelength, long-wavelength, and far-Infrared.
- It can penetrate dense regions of gas & dust in space with less scattering & absorption.
- Its heating effect can cause burns on human skin.
- It's not visible to the naked eye.
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Sample Questions
Ques. What are the applications of electromagnetic waves in our everyday life? (1 mark)
Ans. Electromagnetic waves have a vast range of practical applications in our daily life. Its application includes WIFI, cell phone & radio broadcasting, cooking, medical, and even for treating cancer, etc.
Ques. Name the waves that are present in the electromagnetic spectrum. Which wave has the longest wavelength? (3 marks)
Ans. There are usually 7 different types of EM waves in the electromagnetic spectrum the names of which are mentioned in the list below:
- Gamma rays
- X-rays
- Ultraviolet radiation
- Visible light
- Infrared radiation
- Microwaves
- Radio waves
Out of these wavelengths, the radio wave has the longest wavelength.
Ques. How are infrared radiations produced? (1 mark)
Ans. The EM radiations are produced when there is a change in the velocity of any charged particle such as the electron. In short, they are produced through the vibrations of atoms and molecules.
Ques. Why is infrared radiation referred to as heat waves? (1 mark)
Ans. The reason behind referring to Infrared radiation as heat waves is that the water molecules which are present in most of materials readily absorb Infrared radiation. After the absorption, their thermal motion starts increasing which means they start heating up and their surroundings.
Ques. Name the instrument used to measure the infrared radiation. (1 mark)
Ans. The measuring instrument used to measure Infrared radiation is known as an Infrared thermometer.
Ques. Write a few properties of the infrared waves. (2 marks)
Ans. A few properties are:
- Infrared radiation travels at the speed of 299,792,458 meters per second.
- Infrared lights can reveal both the wave and particle nature at the same time.
- Infrared radiation can either be absorbed or reflected back depending on the surface nature of the material.
- It helps in increasing the thermal energy in the particles.
Ques. What are the uses of infrared radiation in medical therapy? (2 marks)
Ans. A few uses are:
- Helps in the reduction of the swelling of the ear, nose, and throat.
- Acts as an aid in managing stress.
- Helps in reducing arthritis pain.
- Helps in the proper functioning of the kidney.
Ques. How to select infrared radiations? (5 marks)
Ans. guidelines are as follows:
- Proper measurement of the temperature in wavelength of the particular object needs to be noted.
- The photosensitivity and signal-to-noise must be considered along with the signal noise reduction, the infrared detector must be cooled with the use of either thermoelectric cooling or by cryogenic cooling, or mechanical cooling.
- The response speed and shopping frequency must be properly recorded depending on the infrared detector application.
- The geometry and the size of the active area play an important role when intra-detectors are being used.
- We can get infrared detectors in various kinds of packaging which includes metal can packages or ceramic packages.
Ques. What is the classification of the infrared detectors? (1 mark)
Ans. There can be two classifications of infrared detectors which are as follows:
- Thermal infrared detectors
- Quantum infrared detectors.
Ques. What are the characteristics of infrared radiation? (4 marks)
Ans. A few of the characteristics of infrared radiation are as follows:
- The wavelength of IR ranges from 700-1 nanometer.
- Its frequency ranges from 430 THz – 300 GHz
- Infrared radiation is a Transverse wave
- Unlike visible light, they show the property of Refraction
- It originates from an alteration in electron movement.
- It consists of heat-inducing properties.
- The wavelength of Near-Infrared rays is close to that of visible light. They can be used in the TV remote, photography, etc.
- The Far-Infrared rays are more thermal as compared to near-infrared wavelengths.
Ques. Which radiation is used for eye surgery? (2019)
Ans. Infrared radiation is used for eye surgery.
Ques. Why are infrared waves often called heat waves? Explain. (2018)
Ans. Infrared waves are often called heat waves because they increase the temperature of the body of the object on which they fall, as a result increasing the thermal motion. They also have an impact on the photographic plate and most of the materials absorb them.
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