Waves… a review
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Most waves are either longitudinal or transverse.
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Sound waves are longitudinal.
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But all electromagnetic waves are transverse…

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Electromagnetic waves
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Produced by the movement of electrically charged particles
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Can travel in a “vacuum” (they do
NOT need a medium
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Travel at the speed of light
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Also known as EM waves

Wave-particle Duality
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Light can behave like a wave or like a particle
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A “particle” of light is called a photon

Radio waves
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Longest wavelength EM waves
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Uses:
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TV broadcasting
AM and FM broadcast radio
Avalanche beacons
Heart rate monitors
Cell phone communication

Microwaves
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Wavelengths from 1 mm- 1 m
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Uses:
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Microwave ovens
Bluetooth headsets
Broadband Wireless Internet
Radar
GPS

Infrared Radiation
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Wavelengths in between microwaves and visible light
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Uses:
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Night vision goggles
Remote controls
Heat-seeking missiles

Visible light
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Only type of EM wave able to be detected by the human eye
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Violet is the highest frequency light
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Red light is the lowest frequency light

Ultraviolet
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Shorter wavelengths than visible light
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Uses:
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Black lights
Sterilizing medical equipment
Water disinfection
Security images on money

Ultraviolet (cont.)
UVA UVB and UVC
Energy Highest of UV waves
Health risks
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Extremely low risk for
DNA damage
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Can destroy
Vitamin A in skin
Lower than UVA
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Can cause DNA damage, leading to skin cancer
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Responsible for sunburn

X-rays
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Tiny wavelength, high energy waves
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Uses:
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Medical imaging
Airport security
Inspecting industrial welds

Gamma Rays
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Smallest wavelengths, highest energy EM waves
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Uses
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Food irradiation
Cancer treatment
Treating wood flooring

Calculations with Waves
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Frequency: number of wave peaks that occur in a unit of time
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Measured in Hertz (Hz)
Represented by nu (v)
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Wavelength: the distance between wave peaks
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Represented by lambda (λ) c= λv, c=3.0 x 10 8 m/s

Understanding
Wavelength/Frequency
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If the wavelength is longer, the frequency is low
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If the wavelength is shorter, the frequency is high

Practice
A certain green light has a frequency of 6.26 x 10 14 Hz.
What is its wavelength?

Max Planck
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Assumed energy was given off in little packets, or quanta (quantum theory)
He called these quanta photons.
He determined the energy of this quanta of light could be calculated
E=hv
E: quantum of energy h: constant, 6.626 x 10 -34 J/Hz v: frequency of the wave

Practice
What is the energy content of one quantum of the light in the previous problem?

Bohr Model of Atom
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Proposes that the atom is
“quantized”
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As electrons move around the nucleus, they have specific energies
Only certain electron orbits (energy levels) are allowable

Bohr Model
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Atoms are most stable when their electrons are orbiting around the atom with the lowest possible energies. This lowest energy state is the ground state.
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If the electrons absorb energy, the atom can leave the ground state and jump to a higher energy state called the excited state.

Bohr Model
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The electron jump (a quantum leap) occurs when an atom absorbs a packet of electromagnetic energy called a photon.
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Only photons of certain energies are absorbed during this process

Quantum Leaps
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Create a high energy state for the atom which is not favored by nature and is unstable
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Electrons immediately release the energy that they absorbed to return back to ground state

Energy Released
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The energy is released as specific energies of visible light which we see as different colors

Types of Spectra
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Absorption (dark-line) spectra appear as a rainbow of colors with dark lines in it. Each dark line represents a specific amount of energy that an electron absorbs as it quantum leaps into a higher energy orbit

Types of Spectra
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Emission (bright-line) spectra appear as a dark background with lines of color in it. Each colored line represents a specific amount of energy that an electron releases as it quantum leaps back to its original orbit.

What do you notice?

Analyzing Spectra
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Analysis of the spectra of different substances is the basis for spectroscopy
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The study of the energy which is given off and absorbed when atoms go from the ground state to the excited state and back again

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Image credits
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http://www.antonineeducation.co.uk/New_items/MUS/images/Making6.gif
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http://abyss.uoregon.edu/~js/glossary/wave_particle.html
http://www.astro.princeton.edu/~gk/A402/electromagnetic_spe ctrum.jpg
http://science.hq.nasa.gov/kids/imagers/ems/radio.html
http://www.nentjes.info/Palace/radio-6.gif
http://www.mobilewhack.com/motorola-h12-bluetoothheadset.jpg
http://www.stuffintheair.com/radar-real-time-weather.html
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http://www.georgiaprismaward.com/The_Prism_Story_files/PRI
SM%20brand%20imagemed.jpg
http://science.hq.nasa.gov/kids/imagers/ems/uv.html

Image Credits
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http://farm3.static.flickr.com/2385/2381723771_12548f
4bd1.jpg?v=1217429879 http://intamod.com.au/images/uv2.JPG
http://science.hq.nasa.gov/kids/imagers/ems/xrays.html
http://www.sciencelearn.org.nz/var/sciencelearn/storage
/images/contexts/see_through_body/sci_media/neck_x_r ay/17945-5-eng-NZ/neck_x_ray_full_size_portrait.jpg
http://www.epinion.eu/wordpress/wpcontent/uploads/2008/05/airport-security1.jpg
http://science.hq.nasa.gov/kids/imagers/ems/gamma.ht
ml http://www.aboutnuclear.org/print.cgi?fC=Food http://www.roswellpark.org/files/1_2_1/brain_spinal/ga mma%20knife%204c.jpg