Fig.2.6 High E: High freq. & low Low E: Low freq. & high.
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Fig.2.6
High E: High freq. & low Low E: Low freq. & high
Radiation from the Sun (Fig 2.7)
(most intense) (most abundant)
(most damaging!)
(2.5) Radiation and Matter
“Particles” of Energy
Max Planck:Radiation is quantized – exists only at certain energy levels
Frequency
Energy
Radiation exists onlyat these energy levels
Not between
Einstein: One “step” = photon“bundle of light energy”
New way of thinking about light:Light is a particleHas no massMoves in waves
Calculating the Energy of Light:
Unit of energy: joule (J)
Accelerate a 1 kg mass
from 0 to 1 m/s
over a distance of 1 m
(1 heartbeat)
Equation: E=h
Planck’s Constant: 6.63 x 10-34 J·s
What is the energy of UV light with a frequency of 1.00 x 1015 s-1
E = h = (6.63 x 10-34 J·s)(1 x 1015 s-1)
E = 6.63 x 10-19 J
Compare to radio wave of 3 x 109 m
E = hc = (6.63 x 10-34 J·s)(3.00 x 108 m/s) 3 x 109 m
E = 6.63 x 10-35 J
Can also calculate energy from
E = hhc (since = c)
UV has 10 quadrillion times more energy!
What happens when light hits matter?
IR – molecules vibrate, matter heats up
Visible – excite electrons, chemical reactions can occur (photosynthesis)
UV – knock electrons off charged particles
High freq. UV – break covalent bonds (!)(disrupt biol. processes, damage tissues, cancer)
Fig.02.11≤
+
≤
+
Fig. 2.9:Chapman Cycle
(Ozone = steady state)
UV Absorption by O2 and O3
Oxygen: 200-242 nm
Ozone: 200-320 nm Why does ozone absorb a broader range?
It’s more reactive!
O O
O
O
O
“Bond-and a half” weaker than double bond Lower energy light can react
Fig. 2.10
DNADamage
Cause for Concern
• Short = massive DNA cleavage
• 280 nm is 100,000X more damaging than 320nm
• Ozone conc. has been dropping More short light gets thru More damage to organisms
1% decrease in O3 = 2% increase in skin cancer
Skin Cancer
• Awareness: increased
• Treatments: improved– Early detection
• Trend: on the rise!
Reasons
• Ozone depletion – partly responsible
• Geographic location
• More people in outdoor activities?
• Tanning beds?
Tanning
• Cosmetic benefit vs. cancer risk
• Cancer can occur after exposure has stopped
• Advance ageing process
• Highest risk: Fair hair & skin
• Winter– Snow-blindness, cataracts from UVB
Other facts
• Geographical location – big factor!• Sunblock helps
– Not immune!• UVB harms other organisms
– Plants– Marine life (phytoplankton)
• Ultimate food source for ocean life
• Absorb 80% of man-made CO2
–Greenhouse gas
Fig. 2.13
O3 Decline – Our Fault?
• Natural fluctuations:
– Seasonal variation in UV intensity
– Sunspot activity cycles (1-2% effect)
– Wind
– Random fluctuations
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