Light as a Wave
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![Page 1: Light as a Wave](https://reader035.fdocuments.in/reader035/viewer/2022062221/56813521550346895d9c85b3/html5/thumbnails/1.jpg)
Light as a Wave OBJECTIVES:
• Describe the relationship between the wavelength and frequency of light.
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Electrons and Light After Bohr’s model, the mystery of the
atom was the nature of the electron cloud.
The study of light – particularly the wave nature of light – played a critical role in probing the nature of the electron cloud.
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Light and Energy are Linked Energy travels through space as light
waves. These Light waves are known as
Electromagnetic Radiation (EMR) EMR – defined as a form of energy
that exhibits wavelike behavior as it travels trough space.
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Types of EMR Visible Light is one type of EMR Others include x-rays, microwaves,
radiowaves, gamma rays, ultraviolet waves, infrared waves.
All electromagnetic radiation travels at this same rate.
This rate is the speed of light (c) c = 3.0 x 108 m/sec
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- Page 139
“R O Y G B I V”
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Basic Properties of Waves Wavelength (λ- lambda) – distance
between two crests of a wave. Units are usually meters.
Frequency (f or (nu) )- the number of wave cycles that pass a given point per unit time (usually seconds) Units are sec-1 = Hertz
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Parts of a wave
Wavelength
AmplitudeOrigin
Crest
Trough
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Wavelength and Frequency Are inversely related
• As one goes up the other goes down.
• c = or c = f
c = speed of light = 3.0 x 108m/s
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As frequency decreases, wavelength increases.
As frequency increases, the wavelength decreases.
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Different frequencies of light are different colors of light.
There is a wide variety of frequencies
The whole range is called a spectrum
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EM Spectrum
LOW
ENERGY
HIGH
ENERGY
R O Y G. B I V
red orange yellow green blue indigo violet
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Equation: E = hf
EE = Energy, in units of Joules (kg·m = Energy, in units of Joules (kg·m22/s/s22)) (Joule is the metric unit of energy)(Joule is the metric unit of energy)
hh = Planck’s constant (6.626 x 10 = Planck’s constant (6.626 x 10-34-34 J·s) J·s)
f f = frequency, in units of hertz (hz, sec= frequency, in units of hertz (hz, sec-1-1))
The energy (E ) of electromagnetic radiation is directly proportional to the frequency () of the radiation.
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Low ENERGYWaves
=Long
Wavelength=
Low Frequency
High ENERGYWaves
=Short
Wavelength=
High Frequency
Wavelength Table
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Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Low Frequency
High Frequency
Long Wavelength
Short WavelengthVisible Light
Low Energy
High Energy
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Behavior of Light That Supports Wave Theory
Reflection — Waves rebound from a collision with an even substance at the same angle which they approached it.
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Refraction — Waves change speed when they enter a new medium (from air to water).
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Refraction explains how a prism separates the colors that make up white light.
Each color will refract (or bend) to different degrees based on its characteristic wavelength
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Diffraction — Waves can interfere with other waves
They create diffraction patterns Constructive interference—occurs
when a crest meets a crest or a trough meets a trough
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Destructive interference—occurs when a crest meets a trough
For light waves, you see darkness with destructive interference.
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• Microwaves are used to transmit information.
Calculating Wavelength of an EM Wave
• What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz?
• Solve the equation relating the speed, frequency, and wavelength of an electromagnetic wave for wavelength (λ).
Electrons in Atoms: Basic ConceptsElectrons in Atoms: Basic ConceptsElectrons in Atoms: Basic ConceptsElectrons in Atoms: Basic ConceptsTopic 9Topic 9
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• Substitute c and the microwave’s frequency, , into the equation. Note that hertz is equivalent to 1/s or s–1.
Calculating Wavelength of an EM Wave
Electrons in Atoms: Basic ConceptsElectrons in Atoms: Basic ConceptsElectrons in Atoms: Basic ConceptsElectrons in Atoms: Basic ConceptsTopic 9Topic 9
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Examples2) What is the frequency of red light with a
wavelength of 4.2 x 10-5 m?
3) What is the energy of the photon above?
c = λf or f = c/λ
f = 3.0 x 108m/s
4.2 x 10-5 m= 7.1 x 1012 sec-1
E = hfE = (6.626 x 10-34 J sec) (7.1 x 1012 sec-1)
E = 4.73 x 10-21 Joules