Topics for Today Properties of Light Sunscreen and the Ozone Layer! Quiz #4

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