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Light is a form of electromagnetic radiation that propagates in free space or vacuum perpendicular to the direction of oscillations of the photons of the transverse wave. The sun is the primary source of light energy (polychromatic light), also known as white light, containing seven colours of the visible spectrum. The electromagnetic spectrum consists of different wavelengths. A wavelength is the total distance between two similar points on two consecutive waves. The wave number is the reciprocal of wavelength analogous to frequency. A detailed view is described below.
Wavelength:
- Wavelength can be described as the distance between two crests or two troughs of a wave. Waves can be of any nature (e.g., sound waves, electromagnetic waves, etc.).Â
- A trough is the lowermost point of the wave, and a crest is the topmost point of the wave.Â
- Wavelength is denoted by the symbol lambda (λ), a Greek symbol.
- If a wave is of higher frequency, it will have a shorter wavelength, while the one with a lower frequency will possess longer wavelengths.
- Red colour has the longest wavelength and shortest frequency, whereas violet colour has the shortest wavelength and highest frequency in the visible spectrum.
- Spectrum is the range of frequencies or wavelengths (electromagnetic spectrum, sound spectrum, vibration spectrum).
- Visible light depicts a wavelength of 300-700 nm.
- Frequency is inversely proportional to the wavelength.
- The human eye can only detect the visible region of the electromagnetic spectrum; other rays such as X-rays, gamma rays, infrared rays, and ultraviolet rays are not visible to the naked eye.
- A particular wavelength depends on the medium through which it travels; the medium can be a vacuum, air, or water.
- A light wave can be portrayed as a variation in the strength of electric and magnetic fields, while a variation in air pressure is a sound wave.
The formula for wavelength:
- Wavelength is denoted by the symbol lambda (λ).Â
- The formula to calculate wavelength:Â
                 λ = v/fÂ
Where, f symbolises the frequency and v symbolises velocity.
- The unit of wavelength – metre (m), frequency – Hz, and velocity – m/s.
Types of wavelengths:
The whole electromagnetic spectrum is partitioned into seven segments: Radio waves, gamma rays, X-rays, ultraviolet rays, microwaves, infrared waves, and the visible spectrum.
Applications:
- Gamma Radiations:
- Various medical applications include radiation therapies and positron emission tomography (PET) to treat malignant or stagnant cancerous tumours.
- They are used to sterilise medical equipment before surgery.
- They are useful for diagnostic purposes in imaging techniques of nuclear medicine.
- They are also used in a Computed Tomography Scanner or CT-Scan.
- They kill various viruses and bacteria in food and crops.
- They are also used to carry out plant breeding processes with mutation techniques.
- X-Rays:
- The most prominent use of X-rays is X-ray radiography, which helps detect and diagnose bone fractures, tumours, arthritis, dental issues, calcifications, and heart problems.
- They are used to determine the structures of crystalline materials and differentiate between amorphous and crystalline materials.
- X-rays can predict the atomic arrangements and thickness of films and multilayers.
- Ultraviolet radiations:
- They are used for sterilisation purposes and to create fluorescent effects.
- They are also used in tanning machines where the skin is exposed to U.V. rays and the radiations are absorbed by melanin pigment creating the heating effect.
- They are used in chemistry to analyse chemical structures through colour variations.
- They are also useful in treating diseases, such as psoriasis and numerous dermatological conditions.
- Visible Spectrum:
- It is used for indoor navigation and underwater communication.
- It is useful for photography and optical microscopy.
- The human eye can see and detect colours because of the visible spectrum.
- It is also used in astronomy.
- Infrared Rays:
- They are majorly used in forensic science to analyse fragments of paints from vehicles in hit-and-run cases.
- They can be used for quality control during perfume manufacturing and drug analysis.
- They are also used in telescopy and reveal information that visible rays cannot detect.
- Microwaves:
- The crucial use of microwaves is in heating appliances, such as microwave ovens, to bake cookies and cakes.
- They are also used for satellite communication in military operations.
- They are also used in telecommunication transmission and broadcasting because a small antenna can be fitted due to shorter waves transmission.
- Radio Waves:
- They are used in broadcasting television and radio programmes using modern technologies.
- Navigation and air traffic control centres also use radio waves for communication.
- They are also used for radio detection and ranging; the acronym is RADAR.
- Radio telemetry is used to locate an animal’s precise position and movement.
Angular Wave Number:
- The wave number or repentance is the measure of cycles per unit distance.
- The number of radians per metre is called the angular wave number.Â
- The S.I. unit of angular wave number is radians per metre (rad/m), where radian is a dimensionless quantity.
- The formula used to denote angular wave number is –Â
  k = 2 π/λ OR 2 πv/vp OR w/vp
Where, (λ) is the wavelength, v is the frequency of the specific wave, w is the angular frequency of the wave, and vp is the phase velocity of the wave.
- The radians per unit time are known as the angular frequency.
- Wave numbers play a key role in sectors of optics, neutron diffraction, electron diffraction, and elementary particles.
- The angular wave number is inversely proportional to the wavelength; this relation can be seen through the formula given below:
     k = 2π/λ
Conclusion:Â
This article gave an overview of wavelength, angular wave number, and the relation between angular wavenumber and wavelength. It also discusses some important applications, frequencies, and wavelengths of different waves in the electromagnetic spectrum. The above article will be beneficial for the students preparing for NEET and JEE Mains/Advance examinations.
