<< Chapter < Page Chapter >> Page >

Electromagnetic radiation allows us to observe the world around us. It is this radiation which reflects off of the objects around you and into your eye. The radiation your eye is sensitive to is only a small fraction of the total radiation emitted in the physical universe. All of the different fractions taped together make up the electromagnetic spectrum.

Dispersion

When white light is split into its component colours by a prism, you are looking at a portion of the electromagnetic spectrum.

The wavelength of a particular electromagnetic radiation will depend on how it was created.

Wave nature of em radiation

  1. List one source of electromagnetic waves. Hint: consider the spectrum diagram and look at the names we give to different wavelengths.
  2. Explain how an EM wave propagates, with the aid of a diagram.
  3. What is the speed of light? What symbol is used to refer to the speed of light? Does the speed of light change?
  4. Do EM waves need a medium to travel through?

The radiation can take on any wavelength, which means that the spectrum is continuous. Physicists broke down this continuous band into sections. Each section is defined by how the radiation is created, not the wavelength of the radiation. But each category is continuous within the min and max wavelength of that category, meaning there are no wavelengths excluded within some range.

The spectrum is in order of wavelength, with the shortest wavelength at one end and the longest wavelength at the other. The spectrum is then broken down into categories as detailed in [link] .

Electromagnetic spectrum
Category Range of Wavelengths (nm) Range of Frequencies (Hz)
gamma rays < 1 > 3 × 10 19
X-rays 1-10 3 × 10 17 - 3 × 10 19
ultraviolet light 10-400 7 , 5 × 10 14 - 3 × 10 17
visible light 400-700 4 , 3 × 10 14 - 7 , 5 × 10 14
infrared 700- 10 5 3 × 10 12 - 4 , 3 × 10 19
microwave 10 5 - 10 8 3 × 10 9 - 3 × 10 12
radio waves > 10 8 < 3 × 10 9

Since an electromagnetic wave is still a wave, the following equation that you learnt in Grade 10 still applies:

c = f · λ

Calculate the frequency of red light with a wavelength of 4 , 2 × 10 - 7  m

  1. We use the formula: c = f λ to calculate frequency. The speed of light is a constant 3 × 10 8 m/s.

    c = f λ 3 × 10 8 = f × 4 , 2 × 10 - 7 f = 7 , 14 × 10 14 Hz
Got questions? Get instant answers now!

Ultraviolet radiation has a wavelength of 200 nm . What is the frequency of the radiation?

  1. Recall that all radiation travels at the speed of light ( c ) in vacuum. Since the question does not specify through what type of material the Ultraviolet radiationis traveling, one can assume that it is traveling through a vacuum. We can identify two properties of the radiation - w a v e l e n g t h ( 200 nm ) and speed ( c ).

  2. c = f λ 3 × 10 8 = f × 200 × 10 - 9 f = 1 . 5 × 10 15 Hz
Got questions? Get instant answers now!

Examples of some uses of electromagnetic waves are shown in [link] .

Uses of EM waves
Category Uses
gamma rays used to kill the bacteria in marshmallows and to sterilise medical equipment
X-rays used to image bone structures
ultraviolet light bees can see into the ultraviolet because flowers stand out more clearly at this frequency
visible light used by humans to observe the world
infrared night vision, heat sensors, laser metal cutting
microwave microwave ovens, radar
radio waves radio, television broadcasts

In theory the spectrum is infinite, although realistically we can only observe wavelengths from a few hundred kilometers to those of gamma rays due to experimental limitations.

Humans experience electromagnetic waves differently depending on their wavelength. Our eyes are sensitive to visible light while our skin is sensitive to infrared, and many wavelengths we do not detect at all.

Em radiation

  1. Arrange the following types of EM radiation in order of increasing frequency: infrared, X-rays, ultraviolet, visible, gamma.
  2. Calculate the frequency of an EM wave with a wavelength of 400 nm.
  3. Give an example of the use of each type of EM radiation, i.e. gamma rays, X-rays, ultraviolet light, visible light, infrared, microwave and radio and TV waves.

The particle nature of electromagnetic radiation

When we talk of electromagnetic radiation as a particle, we refer to photons, which are packets of energy. The energy of the photon is related to the wavelength of electromagnetic radiation according to:

Planck's constant

Planck's constant is a physical constant named after Max Planck.

h = 6 , 626 × 10 - 34 J · s

The energy of a photon can be calculated using the formula: E = h f or E = h c λ . Where E is the energy of the photon in joules (J), h is planck's constant, c is the speed of light, f is the frequency in hertz (Hz) and λ is the wavelength in metres (m).

Calculate the energy of a photon with a frequency of 3 × 10 18  Hz

  1. E = h f = 6 , 6 × 10 - 34 × 3 × 10 18 = 2 × 10 - 15 J
Got questions? Get instant answers now!

What is the energy of an ultraviolet photon with a wavelength of 200 nm?

  1. We are required to calculate the energy associated with a photon of ultraviolet light with a wavelength of 200 nm.

    We can use:

    E = h c λ
  2. E = h c λ = ( 6 , 626 × 10 - 34 ) 3 × 10 8 200 × 10 - 9 = 9 , 939 × 10 - 10 J
Got questions? Get instant answers now!

Exercise - particle nature of em waves

  1. How is the energy of a photon related to its frequency and wavelength?
  2. Calculate the energy of a photon of EM radiation with a frequency of 10 12  Hz.
  3. Determine the energy of a photon of EM radiation with a wavelength of 600 nm.

Questions & Answers

how is ester formed
Aubrey Reply
how is n ester formed
Aubrey
Alcohol reacts with a carboxylic acid
Texas
an athlete with a mass of 70kg runs at a velocity of 45km . determine the athlete's momentum
Lesedi Reply
Is that a velocity or something else
msawenkosi
45km/h i guess
Texas
Change to m/s
Texas
45km/h = 12.5 m/s p=mv =70×12.5 =875 kg.m/s
Thato
what are the measures of the rates of reaction
Lesego Reply
Volume Concentration Temperature Pressure Surface Area
Thato
the principle of superposition of waves
Sfundo Reply
what is work
Kool Reply
is this a group chat
Nobuhle Reply
Hey can y'all define newton's 2nd law
mthebzification
If a resultant force act on an object...the object will accelerate in the direction of a resultant force,the acceleration of the object is directly proportional to the net force and inversely proportional to the mass of the object
mosa
how do you calculate tension force
Bulumko
use the formula Fnet=ma if there is tension connecting two objects
Sboniso
to calculate Tension, usually calculate acceleration first Draw separate free body diagrams for each body. Apply Fnet = ma to calculate Tension
Kevin
Hi people
Paul
how does temperature affect the equilibrium position
Blessing Reply
an increased temperature increases the average kinetic energy thus in turn increases the number of effective collisions........
Lwando
so...which reaction is favored between endothermic and exothermic .when temperature is increased..?
Blessing
exothermic reaction because energy is realised to the surroundings as heat and light energy ....graphical so much energy is realised as reactants to form product and because temperature is high rate of reaction is fast which means there is a successful collision
Code
INTEMENDO - INCREASE IN TEMPERATURE FAVOURS ENDOTHERMIC DETEMEXO - DECREASE IN TEMPERATURE FAVOURS EXOTHERMIC
Thato
an object will continue in a state of rest unless it is acted upon an unbalanced force
Junior Reply
Newton's Law 1
Code
First Newton's Law
Azola
Newton's first law
Surprise
newton first law
Thinavhuyo
Newton's first law
Blessing
when pressure is increased what happen to volume
Siphelo Reply
decreases
Code
care to explain?
Mpati
if pressure is applied to a pistol , the volume will decrease and particles will collide more frequently with the wall of a container .Each time they collide with the wall they exert a force on them .More collision means more force and the pressure will increase , that Boyle's Law
Code
Because the volume has decreased , the particle will collide more frequently with the wall of a container and each time they collide with the wall of a container they exert a force on them.More collision means more force so the pressure will increase , that Boyle's Law
Code
what is the difference between momentum and a change in momentum?
Chavonne Reply
How to name a branched molecule from right or left?
Vadin Reply
What's Free Fall
Senzo Reply
Free Fall means there is no acting force on that object.
Dingaletu
only gravitational force
Dingaletu
no external force acting on an object
Sphiwe
by only force of gravite
Sello
but gravitational force
Sphiwe
true
Lucky
a motion in which the only force acting is gravitational force
Blessing
and an object experiencing free fall is referred as a projectile
Blessing
Do polymers form restrictedly only if compound is saturated, only?
milani Reply
what is a free fall?
Beyanca Reply
is when The Only Force acting On an Object is Gravitational Force
Madman
Thats right
Beyanca
then Why ask when you Know the answer?
Madman
She's just helping those who forgot it...bro
Thato
guys I need help on Getting ready for a last minute test
Kenelioe Reply
what help you need
Neil
we'll I'm in grade 12 so we doing this topic about upac thing
Kenelioe
on What?
Madman
the organic molecule section
Kenelioe
IUPAC NAMING WHICH FUNCTIONAL GROUP YOU CANNOT NAME?SO I COULD HELP YOU
Madman
ester
Sboniso
you should also look at structural isomers. Its crucial that they might add that one. also try and write down the structural formula of all the given compounds on the table
milani

Get the best Siyavula textbooks: gr... course in your pocket!





Source:  OpenStax, Siyavula textbooks: grade 12 physical science. OpenStax CNX. Aug 03, 2011 Download for free at http://cnx.org/content/col11244/1.2
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Siyavula textbooks: grade 12 physical science' conversation and receive update notifications?

Ask