# 0.5 Colour

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## Introduction

The light that human beings can see is called visible light . Visible light is actually just a small part of the large spectrum of electromagnetic radiation which you will learn more about in [link] . We can think of electromagnetic radiation and visible light as transverse waves. We know that transverse waves can be described by their amplitude, frequency (or wavelength) and velocity. The velocity of a wave is given by the product of its frequency and wavelength:

$v=f×\lambda$

However, electromagnetic radiation, including visible light, is special because, no matter what the frequency, it all moves at a constant velocity (in vacuum) which is known as the speed of light. The speed of light has the symbol $c$ and is:

$\begin{array}{ccc}\hfill c& =& 3×{10}^{8}\phantom{\rule{3.33333pt}{0ex}}\phantom{\rule{3.33333pt}{0ex}}\mathrm{m}.{\mathrm{s}}^{-1}\hfill \end{array}$

Since the speed of light is $c$ , we can then say:

$c=f×\lambda$

## Colour and light

Our eyes are sensitive to visible light over a range of wavelengths from 390 nm to 780 nm (1 nm = $1×{10}^{-9}$ m). The different colours of light we see are related to specific frequencies (and wavelengths ) of visible light. The wavelengths and frequencies are listed in [link] .

 Colour Wavelength range (nm) Frequency range (Hz) violet 390 - 455 769 - 659 $×{10}^{12}$ blue 455 - 492 659 - 610 $×{10}^{12}$ green 492 - 577 610 - 520 $×{10}^{12}$ yellow 577 - 597 520 - 503 $×{10}^{12}$ orange 597 - 622 503 - 482 $×{10}^{12}$ red 622 - 780 482 - 385 $×{10}^{12}$

You can see from [link] that violet light has the shortest wavelengths and highest frequencies while red light has the longest wavelengths and lowest frequencies .

A streetlight emits light with a wavelength of 520 nm.

1. What colour is the light? (Use [link] to determine the colour)
2. What is the frequency of the light?
1. We need to determine the colour and frequency of light with a wavelength of $\lambda =520$ nm = $520×{10}^{-9}$ m.

2. We see from [link] that light with wavelengths between 492 - 577 nm is green. 520 nm falls into this range, therefore the colour of the light is green.

3. We know that

$\begin{array}{ccc}\hfill c& =& f×\lambda \hfill \end{array}$

We know $c$ and we are given that $\lambda =520×{10}^{-9}$ m. So we can substitute in these values and solve for the frequency $f$ . ( NOTE: Don't forget to always change units into S.I. units! 1 nm = $1×{10}^{-9}$ m.)

$\begin{array}{ccc}\hfill f& =& \frac{c}{\lambda }\hfill \\ & =& \frac{3×{10}^{8}}{520×{10}^{-9}}\hfill \\ & =& 577×{10}^{12}\phantom{\rule{3.33333pt}{0ex}}\phantom{\rule{3.33333pt}{0ex}}\mathrm{Hz}\hfill \end{array}$

The frequency of the green light is $577×{10}^{12}$ Hz

A streetlight also emits light with a frequency of 490 $×{10}^{12}$ Hz.

1. What colour is the light? (Use [link] to determine the colour)
2. What is the wavelength of the light?
1. We need to find the colour and wavelength of light which has a frequency of 490 $×{10}^{12}$ Hz and which is emitted by the streetlight.

2. We can see from [link] that orange light has frequencies between 503 - 482 $×{10}^{12}$ Hz. The light from the streetlight has $f=490×{10}^{12}$ Hz which fits into this range. Therefore the light must be orange in colour.

3. We know that

$\begin{array}{ccc}\hfill c& =& f×\lambda \hfill \end{array}$

We know $c=3×{10}^{8}\phantom{\rule{3.33333pt}{0ex}}\phantom{\rule{3.33333pt}{0ex}}\mathrm{m}.{\mathrm{s}}^{-1}$ and we are given that $f=490×{10}^{12}$ Hz. So we can substitute in these values and solve for the wavelength $\lambda$ .

$\begin{array}{ccc}\hfill \lambda & =& \frac{c}{f}\hfill \\ & =& \frac{3×{10}^{8}}{490×{10}^{12}}\hfill \\ & =& 6.122×10-7\phantom{\rule{3.33333pt}{0ex}}\phantom{\rule{3.33333pt}{0ex}}\mathrm{m}\hfill \\ & =& 612×{10}^{-9}\phantom{\rule{3.33333pt}{0ex}}\phantom{\rule{3.33333pt}{0ex}}\mathrm{m}\hfill \\ & =& 612\phantom{\rule{3.33333pt}{0ex}}\phantom{\rule{3.33333pt}{0ex}}\mathrm{nm}\hfill \end{array}$

Therefore the orange light has a wavelength of 612 nm.

where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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