Wavelength of Light: Visible Light & Spectrum

Wavelength of Light is usually in the range of 400-700 nanometres (nm), corresponding to a frequency of about 750-420 tetrahertz. Frequency and Wavelength are very closely interrelated with one another, especially in terms of light. Since light has both the properties of wave and particle, it can be further defined by two equations:

⇒ \(\begin{array}{l}\nu =\lambda f\end{array}\)

⇒ \(\begin{array}{l}E =hf\end{array}\)

Here, 

• ν = velocity of light
• λ = wavelength of light
• f = frequency of light
• E= energy of light wave
• h = Planck’s Constant ( 6.64 × 10^-34 joule.second)

Wavelengths having a range of four hundred to seven hundred nanometers in between infrared and ultraviolet rays are known as visible light. The frequency that ranges generally between 430 to 750 terahertz is denoted as wavelength. 

Key Terms: Wavelength, Nanometers, Ultraviolet Rays, Visible Light, Light, Light Wave, Lambda, Electromagnetic Radiation

---

What is Wavelength?

[Click Here for Sample Questions]

Wavelength is a property of a wave in which the total distance between two identical points between the two successive waves is to be calculated. Wavelength can be defined as:

• The wavelength can be expressed in lambda (λ) which is a Greek word.
• It can also be defined as the distance between two successive crests or troughs of the light wave.
• Waves are a form of energy wherein the electromagnetic radiation takes on while propagating.
• Wavelength denotes a repeating pattern of travelling energies, like sound or light.
• Wavelength can be expressed by the units micrometers (µm) or nanometers (nm).

Frequency and Wavelength Relationship

Frequency and wavelength are associated with one another, especially relative to light.

• Wavelength can be expressed as the distance between two consecutive troughs or crests.
• While, frequency is the number of waves that pass through a single point within the given time period.
• Frequency and wavelength are inversely proportional, meaning the longer the wavelength, the lower the frequency.
• Frequency is usually higher when wavelength is short.
• Typically, when troughs and crests pass through a particular point when wavelength tends to be short.
• Conversely, frequency is usually lower when wavelength exhibits a longer path.

Also Read:

---

Visible Spectrum 

[Click Here for Sample Questions]

Visible spectrum can be defined as the observable region of the electromagnetic wave which can be visible to the naked human eyes.

• In the electromagnetic spectrum, the visible spectrum ranges from the infrared region to the ultraviolet region.
• The naked human eye can detect the light spectrum which is ranging from violet i.e., 400 nanometres to a red colour i.e., 700 nanometres.
• If there is any other electromagnetic radiation, it will either be too small or too big for the human eye to capture.
• When the visible white light passes through a prism it divides the beam of light into a band of colours.
• The red colour has the longest wavelength and the violet colour has the shortest wavelength.
• These colours automatically arrange themselves according to the wavelength in the same manner as the spectrum of rainbow colours.

Calculation of Wavelength of Light 

As the light has a property of wave and particle, it can be expressed via two equations:

⇒ \(\begin{array}{l}\nu =\lambda f\end{array}\)

⇒ \(\begin{array}{l}E =hf\end{array}\)

In this equation,

• ν = velocity of light
• λ = wavelength of light
• f = frequency of light
• E= energy of light wave
• h = Planck’s Constant ( 6.64 × 10^-34 joule.second)

The first equation will denote the wave nature of light and the second equation will denote the particle nature of the light.

---

Wavelength of Visible Light

[Click Here for Sample Questions]

The wavelength of visible light ranges from 400 nm to 700 nm.

• This spectrum of visible light has numerous different colours and that too every colour with a different wavelength.
• The violet colour is said to have the shortest wavelength whereas the red colour is said to have the longest wavelength.
• The wavelength for various colours of the visible spectrum of light is provided below.

The color, wavelength and frequency can be correlated as per the following table:

White Light

White light extends from 400 nm to 750 nm. When the white light is passed through a prism, a light spectrum is formed due to the refraction of different wavelengths through different angles.

Ultraviolet Light

Ultraviolet Light extends from the end of the visible region and x-ray region in the electromagnetic spectrum. Its name has come due to the reason that it is closest to the violet portion of the visible light and it is in the range of 10 to 400 nm.

Infrared Light

Infrared Light is of longer wavelength than visible light and is close to the visible spectrum of light. It is in the range of 750 nm to 1 mm. These radiations can’t be seen but they can be felt in the form of heat.

Red Light and Orange Light

The wavelengths of Red and Orange light lie between 750 nm to 610 nm and 610 nm to 590 nm respectively and if you want to experience them at the best level then there is no greater example than sunrise and sunset. You can best experience these lights during sunrise and sunset.

Yellow Light

The wavelength of Yellow Light lies between 590 nm and 570 nm. These yellow lights are emitted by low-pressure sodium lamps.

Green Light

The wavelengt of Green Light lies between 570 nm to 500 nm. This can be prominently seen in grass and leaves. We see green colour in the grass and leaves because they reflect green colour and absorb all the other wavelengths.

Blue Light

The wavelengt of Blue Light ranges from 500 nm to 450 nm. The atmosphere scatters the shorter wavelengths efficiently and thus the wavelength corresponding to the blue colour is scattered by the atmosphere. That’s the reason the sky looks blue when we look towards it.

Indigo Light and Violet Light

Indigo is a colour that is under the primary colour blue with its wavelength ranging from 450 nm to 425 nm. Whereas violet is the colour with the shortest wavelength and its wavelength ranges from 425 to 400 nm.

As violet light has a shorter wavelength, it is scattered more effectively by the atmosphere. But, due to the reason that our eyes are more sensitive towards blue colour, the sky instead of looking violet or indigo looks blue in colour.

---

Things to Remember

• Wavelength of light is a part of CBSE class 10 science syllabus.
• It comes under term 1 unit Natural phenomenon and carries a total of 7 to 8 marks. 
• Wavelength of light determines the nature of the light.
• Red coloured light has the longest wavelength.
• Violet coloured light has the shortest wavelength.
• The frequency of a wavelength of light is the number of troughs or crests that pass through a point in one second.
• Electromagnetic rays having frequency less than 400 and more than 700 are very difficult to capture through naked eyes. 

Also Read: