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ELECTROMAGENTIC RADIATION
ELECTROMAGNETIC WAVES
Microwaves
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Electromagnetic spectrum
diameter of an atom ~ 10-10 m
Radiation
power lines
radio
AM FM
TV
microwaves
infrared
light
f (Hz)
50
 (m)
Photon
Energy
(eV)
6
-13
610
9
< 10
9
diameter of nucleus ~ 10-15 m
> 0.3
210
-6
< 410
-6
10
0.3
410
31011
110-3
110-3
11
-3
-3
310
110
110
41014
810-7
2
14
3.910
7.810
-7
2
3.910-7
3
ultraviolet
x-rays
810
410
3
31016
110-8
1102
16
-8
2
310
1020
-rays
-7
18
> 10
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110
110
310-12
4105
310

-10
Currents. Radiation emitted from 50
Hz power lines – are they dangerous?
Currents, electronic circuits. AM FM
radio, TV.
Magnetron.  ~ 10 mm to 30 m can
penetrate atmosphere – satellite
communications, mobile phones,
police radar, microwave cooking
(polar water molecule), medical –
diathermy.
Molecular vibrations & rotations, all
objects. Why do you get warm
standing in the sun? Thermography,
IR satellite images, detecting tumors
& cancers.
Outer electrons, incandescent lamps,
lasers, arcs. Eye sensitive to this
narrow band. White light mixture of
all colours of visible spectrum. TV
(red blue green). If a an uranium atom
enlarged to a size of a pea , red ~ 20
m long.
Sunlight ~ 1017 photons.s-1.m-2. Blue
light photons sufficient energy to
disrupt chemical bonds.
7.71014
-14
Comments
Inner & outer electrons. Ionising (4
eV photons break C-C bonds). Skin
cancers, tans the skin, vitamin D
synthesis, damage to eyes. O3 layer
absorbs UV – protection layer. Can
kill micro-organisms.
Inner electrons, x-ray tubes.
Diagnostic medical-rays. Computed
tomography CT scan. Crystal &
molecular structures.
> 410
3
Nuclei, accelerators. Sterlisation, food
preservation, cancer treatment,
medical diagnosis, flaw detection.
Very penetrating – can pass through
large thickness of concrete.
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MODELS FOR LIGHT
Wave model
c=f
speed of light c = 3.0108 m.s-1
Thomas Young & Augustin Fresnel emr waves
- diffraction & interference of light
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Emission and Absorption of electromagnetic radiation by atoms and
molecules
Most of the chemical and optical
properties of a substance are dependent
upon the outer most bound electrons in
atoms. Each electron is usually in its
ground state – the lowest energy state.
Only when an atom absorbs specific and
sufficient energy can the atom move to a
well-defined higher energy state (excited
state).
energy
excited states
ground state
Resonant Absorption
E2
E1
h f = E2 - E1
E2
E1
h f  E2 - E1
Spontaneous emission
E2
h f = E2 - E1
E1
Excited state
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Oscillating
mixed state
Ground state
~ 10-9 s later
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