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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
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!
Topics for MondayTopics for Monday
UV light and the Ozone LayerUV light and the Ozone Layer
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
Assignment #2Assignment #2
We crashed
the server!!!
Exam #2 MOVED!
NOW March 16 (not March 9)
Topics for TodayTopics for Today
Properties of LightProperties of Light
Sunscreen and the Ozone Layer!Sunscreen and the Ozone Layer!
Quiz #4Quiz #4
Light Can Be…Light Can Be…
Reflected
Transmitted
Absorbed
Light can be absorbed! The amount outgoing light is LESS than the incoming light.
Only for a particular energy (wavelength).
Do sunglasses
absorb light?
Where have we seen the
absorption of light in Chem 108?
NO2+O. NO
Visible light~600 nm
OO2 2 2O2O..
UV <242 nm
Where else will we see
absorption of light?
Lab Next Week!!
SpectrophotometrySpectrophotometry
SpectrophotometrySpectrophotometry
Measures the spectrum of light
SpectrophotometrySpectrophotometry
Measures the spectrum of light
How does spectrophotometry
work?
SpectrophotometrySpectrophotometry
Detector
Light SourceSample
(Absorbs Light)
The SpectrophotometerThe Spectrophotometer
Detector
The SpectrophotometerThe Spectrophotometer
Detector
This spectrophotometer has This spectrophotometer has twotwo light sources! light sources!
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?
This spectrophotometer has This spectrophotometer has twotwo light sources! light sources!
2) Visible Source2) Visible Source
HalogenHalogen Lamp Lamp
The SpectrophotometerThe Spectrophotometer
Detector
The sample holderThe sample holder Sample Cuvette
The SpectrophotometerThe Spectrophotometer
Detector
DetectorMeasures the light at each wavelength that passes through the sample!
And this leads to…
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
Figure 2.7Figure 2.7
p. 76p. 76
What is a nanometer
?
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!
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?
What is UV-A
and UV-B?
What does the SPF #
mean?
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…
Octinoxate (5.25%)
Oxybenzone (3.4%)
What energy does it
absorb?
Where is visible light?
200 nm 400 nm
VISIBLE
ULTRAVIOLET RADIATION
UV-AUV-BUV-C
320 nm280 nm
Which is the lowest energy?
200 nm 400 nm
ULTRAVIOLET RADIATION
UV-AUV-BUV-C
320 nm280 nm
UV-AUV-A
Wavelength = 320 – 400 nmWavelength = 320 – 400 nm
Responsible for suntanResponsible for suntan
What is a
suntan?
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!
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)
Although, there are ways to “reverse” the aging process…
?
Octinoxate (5.25%)
Does sunscreen
absorb UV-A?
Yes, some…
UVA
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.
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.
UV-AUV-A
““Black” LightBlack” Light
Rocks and MineralsRocks and Minerals
Optical Brighteners!Optical Brighteners!
blue lightblue light + + yellow lightyellow light = white light! = white light!white light!
FluorescenceFluorescenceWhat is
going on here?
Reflected
Transmitted
Absorbed
Which is it?
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