Topics for Today

1
Topics for Today

• Properties of Light
• Sunscreen and the Ozone Layer!
• Quiz 4

2
Readings for Today
Spectro-photometry Figure 5.23!
Section 2.4 Waves of Light Section 2.7
Biological Effects of Radiation!
What is the difference between UV-A, UV-B, and
UV-C?
3
Topics for Monday

• UV light and the Ozone Layer

4
Readings for Monday

• Section 2.6 The oxygen / ozone sunscreen
• Section 2.8 Stratospheric Ozone Destruction
• Section 2.10 The Antarctic Ozone Hole A Closer
  Look

5
Assignment 2
We crashed the server!!!
6
Exam 2 MOVED! NOW March 16 (not March 9)
7
Topics for Today

• Properties of Light
• Sunscreen and the Ozone Layer!
• Quiz 4

8
Light Can Be
9
Light can be absorbed! The amount outgoing light
is LESS than the incoming light. Only for a
particular energy (wavelength).
10
Do sunglasses absorb light?
Where have we seen the absorption of light in
Chem 108?
11
Visible light 600 nm

O.
NO2
NO
12
Where else will we see absorption of light?
UV lt242 nm
O2 2O.

13
Lab Next Week!!
14
Spectrophotometry
15
Spectrophotometry
Measures the spectrum of light
16
Spectrophotometry
Measures the spectrum of light
How does spectrophotometry work?
17
Spectrophotometry
Detector
Sample (Absorbs Light)
Light Source
18
The Spectrophotometer
Detector
19
The Spectrophotometer
Detector
20

• This spectrophotometer has two light sources!

21

• This spectrophotometer has two light sources!
• The UV Source
• Deuterium lamp

Hmmm What must be true of the quartz casing?
22

• This spectrophotometer has two light sources!
• 2) Visible Source
• Halogen Lamp

23
The Spectrophotometer
Detector
24
Sample Cuvette

• The sample holder

25
The Spectrophotometer
Detector
26
And this leads to
Measures the light at each wavelength that passes
through the sample!
Detector
27
The Spectrum!
Absorbance
Wavelength (nm)
The computer output that allows us to visualize
how much light was absorbed (or transmitted) at
each wavelength.
28
What is a nanometer?
Figure 2.7 p. 76
29

• 1 nanometer (nm) 1 x 10-9 meters 1 billionth
  of a meter.
• 1 nm is to 1 meter as
• 1 foot is to 190,000 miles!

30
Topics for Today
What do sunscreen and the ozone layer have in
common?

• Properties of Light
• Sunscreen and the Ozone Layer!
• Quiz 4

31
What does the SPF mean?
What is UV-A and UV-B?
32
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
33
What energy does it absorb?
Octinoxate (5.25)
Oxybenzone (3.4)
34
(No Transcript)
35
ULTRAVIOLET RADIATION
UV-A
UV-B
UV-C
VISIBLE
200 nm
400 nm
320 nm
280 nm
Which is the lowest energy?
Where is visible light?
36
ULTRAVIOLET RADIATION
UV-A
UV-B
UV-C
200 nm
400 nm
320 nm
280 nm
37
UV-A
What is a suntan?

• Wavelength 320 400 nm
• Responsible for suntan

38
PROTECTION from the UV radiation!
Why does your body produce melanin when exposed
to UV?
An increase in melanin in your skin
Melanin

Pigmentation

Suntan!
39

• Penetrates deeply into the skin (low energy)
• Causes premature aging in skin (wrinkles)

40
Although, there are ways to reverse the aging
process
?
41
Yes, some
Octinoxate (5.25)
Does sunscreen absorb UV-A?
UVA
42
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.
43
UV-A

• Burns your eyes. Effects usually are temporary
• Chronic Exposure can result in a damaged retina
  or cataracts.

44
UV-A

• Black Light

45
Rocks and Minerals
46

• Optical Brighteners!
• blue light yellow light white light!

white light!
47
(No Transcript)
48
Fluorescence
What is going on here?
Which is it?
49
Fluorescence

• A two-step process!!
• 1) Incoming wavelength is absorbed
• 2) Light of a LOWER energy is re-emitted