Topics for Today Properties of Light Sunscreen and the Ozone Layer! Quiz #4.
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Transcript of Topics for Today Properties of Light Sunscreen and the Ozone Layer! Quiz #4.
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Topics for TodayTopics for Today
Properties of LightProperties of Light
Sunscreen and the Ozone Layer!Sunscreen and the Ozone Layer!
Quiz #4Quiz #4
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Readings for TodayReadings for Today
What is the difference
between UV-A, UV-B, and UV-
C?
Section 2.4 Waves of LightSection 2.4 Waves of Light
Section 2.7 Biological Effects of Radiation!Section 2.7 Biological Effects of Radiation!
Spectro-photometry
: Figure 5.23!
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Topics for MondayTopics for Monday
UV light and the Ozone LayerUV light and the Ozone Layer
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Readings for MondayReadings for Monday
Section 2.6 The oxygen / ozone Section 2.6 The oxygen / ozone sunscreensunscreen
Section 2.8 Stratospheric Ozone Section 2.8 Stratospheric Ozone DestructionDestruction
Section 2.10 The Antarctic Ozone Hole: A Section 2.10 The Antarctic Ozone Hole: A Closer Look Closer Look
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Assignment #2Assignment #2
We crashed
the server!!!
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Exam #2 MOVED!
NOW March 16 (not March 9)
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Topics for TodayTopics for Today
Properties of LightProperties of Light
Sunscreen and the Ozone Layer!Sunscreen and the Ozone Layer!
Quiz #4Quiz #4
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Light Can Be…Light Can Be…
Reflected
Transmitted
Absorbed
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Light can be absorbed! The amount outgoing light is LESS than the incoming light.
Only for a particular energy (wavelength).
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Do sunglasses
absorb light?
Where have we seen the
absorption of light in Chem 108?
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NO2+O. NO
Visible light~600 nm
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OO2 2 2O2O..
UV <242 nm
Where else will we see
absorption of light?
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Lab Next Week!!
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SpectrophotometrySpectrophotometry
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SpectrophotometrySpectrophotometry
Measures the spectrum of light
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SpectrophotometrySpectrophotometry
Measures the spectrum of light
How does spectrophotometry
work?
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SpectrophotometrySpectrophotometry
Detector
Light SourceSample
(Absorbs Light)
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The SpectrophotometerThe Spectrophotometer
Detector
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The SpectrophotometerThe Spectrophotometer
Detector
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This spectrophotometer has This spectrophotometer has twotwo light sources! light sources!
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This spectrophotometer has This spectrophotometer has twotwo light sources! light sources!
1)1) The UV SourceThe UV Source
DeuteriumDeuterium lamp lamp
Hmmm…What must
be true of the quartz
casing?
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This spectrophotometer has This spectrophotometer has twotwo light sources! light sources!
2) Visible Source2) Visible Source
HalogenHalogen Lamp Lamp
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The SpectrophotometerThe Spectrophotometer
Detector
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The sample holderThe sample holder Sample Cuvette
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The SpectrophotometerThe Spectrophotometer
Detector
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DetectorMeasures the light at each wavelength that passes through the sample!
And this leads to…
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The Spectrum!The Spectrum!
The computer output that allows us to visualize how much light was absorbed (or transmitted) at each wavelength.
Wavelength (nm)
Abs
orba
nce
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Figure 2.7Figure 2.7
p. 76p. 76
What is a nanometer
?
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1 nanometer (nm) = 1 x 101 nanometer (nm) = 1 x 10-9 -9 meters = 1 meters = 1 billionth of a meter.billionth of a meter.
1 nm is to 1 meter as1 nm is to 1 meter as
1 foot is to 190,000 miles!1 foot is to 190,000 miles!
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Topics for TodayTopics for Today
Properties of LightProperties of Light
Sunscreen and the Ozone Layer!Sunscreen and the Ozone Layer!
Quiz #4Quiz #4
What do sunscreen and the ozone layer
have in common?
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What is UV-A
and UV-B?
What does the SPF #
mean?
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SUN ALERT: Limiting sun exposure, wearing protective clothing, and using sunscreens may reduce the risks of skin aging, skin cancer, and other harmful effects of the sun
The fine print…
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Octinoxate (5.25%)
Oxybenzone (3.4%)
What energy does it
absorb?
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Where is visible light?
200 nm 400 nm
VISIBLE
ULTRAVIOLET RADIATION
UV-AUV-BUV-C
320 nm280 nm
Which is the lowest energy?
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200 nm 400 nm
ULTRAVIOLET RADIATION
UV-AUV-BUV-C
320 nm280 nm
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UV-AUV-A
Wavelength = 320 – 400 nmWavelength = 320 – 400 nm
Responsible for suntanResponsible for suntan
What is a
suntan?
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An increase in melanin in
your skin
Melanin = Pigmentation = Suntan!
Why does your body produce melanin when
exposed to UV?
PROTECTION from the UV radiation!
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Penetrates deeply into the skin (low energy)Penetrates deeply into the skin (low energy)
Causes “premature aging” in skin (wrinkles)Causes “premature aging” in skin (wrinkles)
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Although, there are ways to “reverse” the aging process…
?
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Octinoxate (5.25%)
Does sunscreen
absorb UV-A?
Yes, some…
UVA
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Even careful tanning kills skin cells, damages DNA and causes permanent changes in skin connective tissue which leads to wrinkle formation in later life. There is no such thing as a safe tan.
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UV-AUV-A
Burns your eyes. Effects usually are Burns your eyes. Effects usually are temporarytemporary
Chronic Exposure can result in a damaged Chronic Exposure can result in a damaged retina or cataracts.retina or cataracts.
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UV-AUV-A
““Black” LightBlack” Light
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Rocks and MineralsRocks and Minerals
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Optical Brighteners!Optical Brighteners!
blue lightblue light + + yellow lightyellow light = white light! = white light!white light!
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FluorescenceFluorescenceWhat is
going on here?
Reflected
Transmitted
Absorbed
Which is it?
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A A two-steptwo-step process!! process!!
1) Incoming wavelength is 1) Incoming wavelength is absorbedabsorbed
2) Light of a LOWER energy is 2) Light of a LOWER energy is re-emittedre-emitted
FluorescenceFluorescence