Wavelength of Light - Relationship Between Frequency and Wavelength
Light is the electromagnetic radiation that occurs within a specific section of the electromagnetic spectrum. The term essentially refers to the visible light, it is the light that is distinguishable and visible to naked human eye and it is also responsible for the sense of light. The wavelengths of the visible light range between 400-700 nanometers, this is between the infrared having longer wavelengths and the ultraviolet having shorter wavelengths.
The wavelength of the visible light indicates that its frequency is approximately 430-750 terahertz (THz). The light speed in the vacuum is 299,792,458 metres per second as per the experiment. The visible light like other forms of the electromagnetic radiation moves at this speed specifically in the vacuum. In physics, the definition of light often refers to the electromagnetic radiation having any wavelength, regardless of if it’s visible or not. The forms of radiation such as radio waves, gamma rays, microwaves, and X-rays are all different forms of the light.
The light exhibits both particle nature and wave nature and the occurrence of this phenomenon is described as light's dual nature. Light exists in the form of particles and propagates in the form of wave. The study associated with light is called optics, and optics is an important domain in the study of physics.
Light doesn’t necessarily travel in the straight line but it travels in transverse waves. The wave that is made of oscillation when moving and that occurs perpendicular to direction of energy transfer is known as the transverse waves. Wavelength is essentially the distance between two consecutive troughs or two consecutive crests in the transverse wave. The wavelength is also used for representing repeating pattern of travelling energies, like sound or light.
Wavelength:
We know that light can be understood both as a particle and a wave. Photons are the light particles which exist in the form of "packets" of electromagnetic energy. On the other hand, waves are the form of energy where electromagnetic radiation takes on when it is propagating.
Light does not travel in a straight light line. It travels in the form of a transverse wave. A wave which consists of oscillation while moving which occurs perpendicular to the direction of transfer of energy is called transverse waves. Wavelength is the distance between two consecutive crests or two consecutive troughs in a transverse wave. Wavelength also represents a repeating pattern of any traveling energies, such as light or sound. Wavelength is usually expressed by the units of nanometres (nm) or micrometres (µm). It is represented by the symbol λ which is read as lambda.
The frequency and Wavelength Relationship
The frequency and wavelength are closely associated with each other, especially in relation to light. Wavelength is the distance between two consecutive troughs or crests whereas frequency is defined by the number of waves which pass via a single given point within the specified period of time. The wavelength and frequency are inversely proportional which means the longer the wavelength, the lower is the frequency. The frequency tends to be higher when specifically the wavelength is short since more troughs and crests pass via the specific point when wavelength tends to be short. Conversely the frequency tends to be lower when wavelength exhibits a longer path.
Table of the Wavelengths of Various Colours, and Their Frequencies:
White Light: White light's wavelength extends from 400 to 750 nm. When the white colour is passed through the prism, the light spectrum is formed due refraction of different wavelengths through different angles.
Ultraviolet Light: Ultraviolet light extends from the end of the visible region and the X-ray region in the electromagnetic spectrum. It gets its name as it is the light closest to the violet portion of the visible light and is in the range of 10 to 400 nm.
Infrared Light: Infrared radiation has a longer wavelength than visible light and is close to the red portion of the visible spectrum of light. It extends from 750 nm to 1 mm. Infrared radiation cannot be seen but can be felt in the form of heat.
Red Light and Orange Light: Red light and orange lights whose wavelength lies between 750 to 610 nm and 610 to 590 nm respectively are best viewed naturally during sunrise and sunset. This is because the associated wavelengths of red and orange from sunlight are not properly scattered by the atmosphere during these times.
Yellow Light: Yellow light has a wavelength between 590 and 570 nm. Yellow light is emitted by low-pressure sodium lamps.
Green Light: Green colour, whose wavelength extends from 570 to 500 nm, can be prominently seen in grass and leaves. Grass reflects green wavelength and absorbs all other wavelengths and thus appears green.
Blue Light: Blue light has a wavelength ranging from 500 to 450 nm. The atmosphere scatters shorter wavelengths efficiently and thus the wavelength corresponding to the colour blue is scattered efficiently by the atmosphere. That’s why the sky appears blue when we look up at it.
Indigo Light Violet Light: With a wavelength between 450 and 425 nm, indigo is a colour which is between the primary colour blue and the colour violet in the colour wheel. Violet with a wavelength of 425 to 400 nm is the visible light with the shortest wavelength. It has a shorter wavelength and is hence scattered more effectively by the atmosphere. But since our eyes are sensitive to blue colour, the sky appears blue rather than indigo or violet colour.
FAQs on Wavelength of Light
1. What is the wavelength of light and how is it defined?
The wavelength of light is defined as the spatial period of the electromagnetic wave, representing the distance between two consecutive corresponding points of the wave, such as two adjacent crests or troughs. It is symbolised by the Greek letter lambda (λ). In essence, it measures the length of one full cycle of the light wave.
2. What is the formula relating the wavelength, frequency, and speed of light?
The relationship between the wavelength (λ), frequency (ν), and speed (c) of light in a vacuum is given by the formula: c = λν. This equation shows that wavelength and frequency are inversely proportional. This means that light with a longer wavelength will have a lower frequency, and light with a shorter wavelength will have a higher frequency, as the speed of light in a vacuum is a constant (approximately 299,792,458 metres per second).
3. How does the wavelength of light determine the colour we perceive?
The colour of light that our eyes perceive is directly determined by its wavelength. The human eye is sensitive to a specific range of wavelengths known as the visible spectrum, which spans from approximately 400 nm to 700 nm. Different wavelengths within this spectrum trigger different responses in our eye's cone cells, leading us to perceive them as distinct colours, from violet at the shorter end to red at the longer end.
4. What are the approximate wavelength ranges for the different colours in the visible spectrum?
The visible spectrum of light consists of various colours, each corresponding to a specific range of wavelengths, typically measured in nanometres (nm):
- Violet: 400 – 425 nm
- Indigo: 425 – 450 nm
- Blue: 450 – 500 nm
- Green: 500 – 570 nm
- Yellow: 570 – 590 nm
- Orange: 590 – 610 nm
- Red: 610 – 750 nm
5. Why does the sky appear blue instead of violet, since violet light has a shorter wavelength and should scatter more?
This is an excellent question that involves two main factors. While it's true that shorter wavelengths scatter more effectively (a phenomenon called Rayleigh scattering), and violet light has a shorter wavelength than blue light, the sky appears blue because:
1. The sun emits more light in the blue frequency range compared to violet.
2. More importantly, the cone cells in the human eye are significantly more sensitive to blue light than to violet light. The combination of available blue light and our eyes' sensitivity to it makes us perceive the sky as blue.
6. How does the medium through which light travels affect its wavelength?
When light passes from one medium to another (e.g., from air into water), its speed changes but its frequency remains constant. According to the wave equation (speed = frequency × wavelength), if the speed decreases (as it does in a denser medium like water), the wavelength must also decrease to keep the frequency constant. Therefore, the wavelength of light is shorter in denser media compared to its wavelength in a vacuum.
7. What is the difference between visible light, ultraviolet (UV), and infrared (IR) light based on wavelength?
The key difference is their position on the electromagnetic spectrum, defined by their wavelength:
- Ultraviolet (UV) Light: Has a shorter wavelength than visible light, typically in the range of 10 nm to 400 nm. It is invisible to the human eye.
- Visible Light: Occupies the range from approximately 400 nm (violet) to 750 nm (red). This is the only portion of the spectrum that the human eye can detect.
- Infrared (IR) Light: Has a longer wavelength than visible light, extending from about 750 nm to 1 mm. It is also invisible but can be felt as heat.
8. What is the importance of understanding the dual nature of light when studying its wavelength?
Understanding the dual nature of light—that it behaves as both a wave and a particle (photon)—is crucial. The concept of wavelength is a property of its wave-like behaviour, describing how light propagates through space. However, the energy of light is contained in discrete packets called photons, a property of its particle-like nature. The energy of a photon is inversely related to its wavelength (E = hc/λ), linking these two aspects. This duality is fundamental to explaining phenomena like the photoelectric effect and wave interference.
