5.1 THE NATURE OF LIGHT
Chemistry
Ms. Pollock
2013 - 2014
INTRODUCTION
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Understanding of Rutherford’s model requires
understanding of light
1600s debate about how light travels
Isaac Newton – light beam of particles
● Christian Huygens – light wave of energy
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Neither hypothesis dominant until 1864 wave model
of light (James Clerk Maxwell) accepted by many
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Relationship between magnetism and electricity
● Debate renewed by Max Planck sixty years later
INTRODUCTION
Above left:
Newton;
above right:
Huygens;
below left:
Planck; below
right: Maxwell
THE WAVE FORM OF ENERGY
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Wave model of electromagnetic radiation similar to
waves on rope
Moving rope up and down with one end secured,
motion passed from one part of rope to next
Rope gains wave shape
THE WAVE FORM OF ENERGY
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Crest – highest point of
wave
Trough – lowest point
of wave
No horizontal motion of
particles
Wavelength – distance
from one crest to the
next crest; symbol λ
THE WAVE FORM OF ENERGY
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Amplitude – maximum
height of wave
Velocity – distance
traveled by wave in
one second (unit m/s,
symbol ν)
Frequency – number of
cycles that pass a
given point per unit of
time (unit 1/s or s-1)
Hertz – wave cycles
per second (symbol ƒ)
THE WAVE FORM OF ENERGY
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Velocity, wavelength and frequency related
ν = ƒλ
Velocity = frequency X wavelength
What is the wavelength of a water wave if its
velocity is 5.0 m/s and its frequency is 2.0 s-1?
λ = ν = 5.0 m/s = 2.5 meters
ƒ
2.0 s-1
ELECTROMAGNETIC WAVES
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Form of electromagnetic radiation with electric and
magnetic fields moving at the speed of light
Carry energy from one place to another and are like
waves on rope
Do not require medium
Energy traveling in straight line along path of wave
Associated oscillating electrical field and oscillating
magnetic field
ELECTROMAGNETIC WAVES
ELECTROMAGNETIC WAVES
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Light waves still characterized by wavelength,
frequency, and velocity
Velocity of all electromagnetic waves in vacuum
same value (3.00 X 108 m/s), symbolized by c
c = ƒλ
What is the wavelength of an electromagnetic wave
traveling in air whose frequency is 1.00 X 10 14 s-1?
λ = c = 3.00 X 108 m/s = 3.00 X 10-6 m
ƒ 1.00 X 1014 s-1
THE ELECTROMAGNETIC SPECTRUM
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Frequency related to energy and amplitude of
electromagnetic waves
Frequency able to be converted to energy by
multiplying by Planck’s constant (h = 6.6 X 10-34J⋅s)
E = hƒ
Wide range of frequencies, wavelengths, and
energies in spectrum
Electromagnetic spectrum – range of all
possibilities of electromagnetic radiation
THE ELECTROMAGNETIC SPECTRUM