light & the electromagnetic spectrum
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Light & the Electromagnetic Spectrum. What do you see?. Old woman? Or young girl?. Question. Is turning a light on and off a chemical or physical change? Physical change What creates light?. UV Light. Bohr Model – electrons are found in nrg levels. Visible Light. Infrared Light. - PowerPoint PPT PresentationTRANSCRIPT
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Light & the Electromagnetic Spectrum
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What do you see?Old woman? Or young girl?
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Is turning a light on and off a chemical or physical change?◦ Physical change
What creates light?
Question
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Bohr Model – electrons are found in nrg levels UV
Light
Visible Light
Infrared Light
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Niels Bohr
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1913, looked at a hydrogen atom
Suggested an e- could move between nrg levels if discrete photons or nrg (amounts of nrg) were absorbed or emitted by the e-
e- falls from high low nrg = photon emission◦ Photon has a frequency, or color, that matches the
e- fall
Niels Bohr
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When an electron moves from an excited state to its ground state, light nrg is given off.◦ Excited atom~ e- not in lowest possible nrg
state They have absorbed nrg and jumped to a further nrg
level The color of the light depends on the
amount of nrg. The more nrg levels jumped, the greater the
nrg of light.
Light
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e- at higher nrg states are not stable
These e- want to return to their ground state to become stable◦ Lowest possible nrg level
Distance between nrg levels is NOT all the same.
Light
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R O Y G B I V Blue light has a higher frequency than
red.
Electromagnetic Spectrum
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Frequency – the # of wave cycles passing a point in a period of time.
As frequency increases, wavelength decreases.
wavelength
frequency
lightofspeedc __
sm81000.3
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Planck assumed energy can be released and absorbed in discrete packets called quanta.
The energy of one quanta is:
Where,
known as Planck’s constant.
Max Planck
hE
sJh 341063.6
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Light of a particular wavelength (λ) has a particular frequency (ν) and nrg (E).
If ν, λ or E are known, the other 2 can be calculated.
hE c
smc 81000.3
sJh 341063.6
speed of light
Planck’s constant
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Yellow light given off by a sodium vapor lamp has a wavelength of 589 nm. What is the frequency of this radiation?
Practice
c
smc 81000.3
nmsm
589
1000.3 8
mnm1109
s11009.5 14
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Unit for frequency (ν)◦ Hertz
Unit for wavelength (λ) ◦ Meter (m) or nanometer (nm)
Unit for energy (E)◦ Joule ( J )
Beware of UNITS!
Hzss
11
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Calculate the energy of one photon of yellow light whose wavelength is 589nm.
Practice
hE
ssJ 11009.51063.6 1434
nmsm
589
1000.3 8
mnm1109
s11009.5 14
sJh 341063.6J191037.3
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What do the following symbols stand for? What are their units?
ν
λ
h
c
E
Pop Quiz!
Frequency
Wavelength
Planck’s ConstantSpeed of Light
Energy
ssHz 11
nmm,
sJ
sm
J
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Light’s wave nature is seen as its ability to diffract, reflect, refract.
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Planck stated that nrg is radiated in discrete packets called quanta.
A photon is a quantum of light having the energy
Light’s particle nature is seen by the emission spectra of elements.
Wave Particle Duality of Light
h
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Why each element produces a unique line spectra.
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Eventually leads to a very famous equation by a very famous scientist.
2cmE
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