Transcript Electromagnetic Spectrum and Quantized Energy

Electromagnetic Spectrum
and Quantized Energy
Why the electron is what it is
What is a wave?
A wave is a transfer of energy from
one point to another via a traveling
disturbance
A wave is characterized by its
wavelength, frequency, and
amplitude
Transverse
Waves that travel
perpendicular to
the direction of
motion
Examples: Light,
-p waves
for earthquakes,
Ocean waves
Wavelength (λ)
Distance from
successive crest to
crest or trough to
trough
Measured in
meters
Frequency
Number of crests
passing by per second
Measured in Hertz
(Hz) defined to be one
cycle per sec
Equal to the inverse of
the amount of time it
takes one wavelength
to pass by
Wave Speed
Traveling Waves move through space at a certain speed
 f v
Where,
v is the speed of the wave (m/s)
λ is the wavelength in meters (m)
f is the frequency in Hertz (cycle/s)
Matter / Quantum Waves
Electrons and other tiny particles show
wave-like properties
A particle moving close to the speed of
light (c) can diffract or bend around the
edges of objects
Also, particles do exhibit interference
which is a wavelike property
Any moving matter has wave
characteristics in theory BUT the
wavelength of any life-size particle, like a
golf ball, is so small that it is negligible
To learn about matter waves in depth go
on to the next slide.
If we can sometimes consider an
electron to be a wave, what is its
wavelength?
Its wavelength depends on its
momentum
p
or
h

h

mv
where p is momentum in kg*m/s, h is
Planck’s constant = 6.63 x 10-34 J, and λ
is the wavelength in meters
What is Planck’s constant?
Planck’s Constant is the size where
quantum mechanics becomes necessary
Since "Planck's Constant" (‘h’= 6.63 x 10 34 Js) is such a tiny number, quantum
mechanics is needed only at very small
scales
An electron also has spin that is quantized
in units of h.
These units (Joule-sec) are units of
angular momentum
Electromagnetic Waves
Waves of energy emitted from any accelerating
charges
Any object that is above absolute zero emits
electromagnetic waves
The entire range of possibilities is called the
“Electromagnetic Spectrum”
Still confused? Then click What are
electromagnetic waves?
To learn about the wavelength of photons click to
the next slide.
Electromagnetic Waves
Wavelength is :
c hc
 
f
E
Where,
c is the speed of light (3 x 108 m/s in a vacuum)
λ is the wavelength in meters
f is the frequency in Hertz
And
h is Planck’s constant (there it is again- do you remember its
value?)
E is the energy of a photon in Joules
What is this “photon” term you’re
throwing in there?
A photon is a bundle (quantum) of
light
A photon has energy equal to
E  h
Recall that
h is Plank’s constant
ν is the frequency of the radiation
(wave)
What does a photon do?
Both magnetic and
electric forces
involve the
exchange of
photons
The photon has
zero rest mass, but
has momentum,
can be deflected
gravity, and can
exert a force
X-RAYS
Emitted when an electron
moves from certain
excited states back down
to its ground state, or
when an electron that is
moving very quickly is
suddenly stopped
Two groups - long
wavelength (soft x-rays)
and shorter wavelength
(hard x-rays)
Used for radiography (xray photography) and to
look at materials in
industry for defects
Sources: emitted by
heavy atoms after
bombardment by an
electron
Above the color
violet
Three groups - UV A,
UV B, and UV C.
“A” type: longest
wavelength; least
harmful
UV B and UV C are
absorbed by DNA in
cells
Used by the body to
produce vitamin D, to
kill bacteria on
objects, and for sun
tanning
Sources: Ultra hot
objects 5000°C or
more
ULTRAVIOLET
VISIBLE LIGHT
White light:
combination of all
the colors
Rainbow: example
of white light that
has been separated
into a continuous
spectrum of colors
The names of colors
are assigned in
order of their
wavelengths
Used for
communications
(fiber optics)
Sources: very hot
objects
Color
Wavelength interval
red
~ 625 to 740 nm
orange ~ 590 to 625 nm
yellow
~ 570 to 590 nm
green
~ 490 to 570 nm
blue
~ 440 to 490 nm
Indigo
~ 420 to 440 nm
violet
~ 400 to 420 nm
INFRARED
Thought of as heat
but is not always
Far infrared energy is
heat energy.
All objects that have
warmth radiate
infrared waves
Easily absorbed and
re-radiated.
Used in remote
controls, surveillance,
therapy of muscles
Sources: Humans,
the sun
MICROWAVES
1 mm-1 dm in length
Absorbed by water
molecules – how
microwave ovens heat
food
Used in
telecommunications
and power
transmission
Sources: electric
circuits, many stars,
microwave ovens
10 cm100,000+m in
length
Only cosmic waves
the reach the
surface of the Earth
Cause of noise
Divided into smaller
frequency
dependent groups
called bands
Used
for communications
Sources: transmitt
ers and sparks from
motors
RADIO WAVES
So What is this Quantum Thing?
A Quantum is the Energy required to
jump an Electron from one orbit to
another.