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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 × λ

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:

c = 3 × 10 8 m . s - 1

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

c = f × λ

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] .

Colours, wavelengths and frequencies of light in the visible spectrum.
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 λ = 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

    c = f × λ

    We know c and we are given that λ = 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.)

    f = c λ = 3 × 10 8 520 × 10 - 9 = 577 × 10 12 Hz

    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

    c = f × λ

    We know c = 3 × 10 8 m . s - 1 and we are given that f = 490 × 10 12 Hz. So we can substitute in these values and solve for the wavelength λ .

    λ = c f = 3 × 10 8 490 × 10 12 = 6 . 122 × 10 - 7 m = 612 × 10 - 9 m = 612 nm

    Therefore the orange light has a wavelength of 612 nm.

Questions & Answers

Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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Source:  OpenStax, Maths test. OpenStax CNX. Feb 09, 2011 Download for free at http://cnx.org/content/col11236/1.2
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