climate and global change notes 4-1 energy and radiation energy energy types temperature driven heat...
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Climate and Global Change Notes
4-1
Energy and Radiation
Energy
Energy Types
Temperature Driven Heat Transport
Science Concepts
DefinitionPotentialKineticRadiant
RadiationWave EquationSpectrumStefan-Boltzmann LawWein’s Displacement Law
ConductionConvection
The Earth System (Kump, Kastin & Crane)
• Chap. 3 (pp. 34-41; pp. 45-46)
Climate and Global Change Notes
4-2
Energy
What happens when we drop an object?
What happens when water behind a dam spills to the river below?
What happens when wood burns?
What happens when we turn on a flashlight?
Climate and Global Change Notes
4-3
Energy
Definition
• Energy is the ability to do work
- Work = Force • Distance
- Units
> 1 calorie = energy required to heat 1 gm of water 1°C‡ Note: 1 Calorie (capital C) = 1000 calories = 1 kilocalorie
◊ Unit for food derived energy
Types of Energy
• Potential
- Chemical> Example: a fire
- Electrical> Voltage
‡ Example: a battery uses chemical potential energy to create a voltage and therefore electrical potential energy
Climate and Global Change Notes
4-4
Types of Energy (Con’t)
• Potential (Con’t)
- Gravitational
> Result of object's relative position‡ Example: a falling rock‡ Example: cold (dense) air (fluid) next to warm (less dense)
air (fluid)• Kinetic
- Result of an object's motion
- Large-scale motion
> Example: falling water (hydroelectric power generation)> Example: swinging hammer (drive nail)> Example: air motions, i.e., wind
- Micro-scale motion
> Example: molecular vibration or temperature. Also called thermal energy
Energy (Con’t)
Climate and Global Change Notes
4-5
Heat - Energy Transfer
Types of Energy (Con’t)
• Radiant
- Example: radiation from a fire in a fireplace
- Example: radiation from the Sun
Definition
• Heat - Energy in transit because of a temperature difference
“It is like the advent of thermodynamics … in about 1820. They knew there was something called ‘heat,’ but they were talking about it in terms that would later sound ridiculous.” In fact, he says, they weren’t even sure what heat was, much less how it worked. Most reputable scientists of the day were convinced that a red-hot poker, say, was densely laden with a weightless, invisible fluid known as caloric, which would flow out of the poker into cooler, less caloric-rich bodies at the slightest opportunity. Only a minority thought that heat might represent some kind of microscopic motion in the poker’s atoms. (The minority was right.)
Waldrop, M.M., 1992: Complexity-The Emerging Science at the Edge of Order and Chaos, Touchstone, pp. 297-298.
Climate and Global Change Notes
4-6
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Heat - Energy Transfer
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How about this one ?
And this one ?
Would walk up and pick up this frying pan?
Climate and Global Change Notes
4-7
Heat - Energy Transfer
Three Mechanisms
• Conduction - Objects in contact; molecules bouncing off each other; solids
• Convection - Motion; hot air rises; gases and liquids
• Radiation - Transfer without requiring a medium; vacuum; Electromagnetic waves
ConductionRadiationConvection
Climate and Global Change Notes
4-8
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Conduction - Objects in contact; molecules bouncing off each other; solids
- Caused by uneven temperature
> Examples: Heat conductivity
Material ( cal / s - cm - °C )Air (at 0°C) 0.000058Air (at 20°C) 0.0000614Dry soil 0.0006Dry sand 0.0013Water (at 10°C) 0.00143Concrete 0.0022Wet soil 0.0050Ice (at 0°C) 0.0054Steel 0.121Iron 0.161Aluminum 0.50Copper 0.918
Climate and Global Change Notes
4-9
Heat - Energy Transfer (Con’t)
• Conduction (Con’t)
- New fresh, light snow - Good insulator because of trapped air
- Older settled or wet snow - Not as good an insulator
0.001 0.002 0.003 0.004 0.005
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
0
Conductivity in Snow ( cal / s - cm - °C)
Sno
w D
ensi
ty (
g /
cm
3 )
Climate and Global Change Notes
4-10
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Convection - Motion; hot air rises; gases and liquids
- Caused by uneven heating of fluids
- Thermal circulations; Many sizes
> Clouds
‡ Convective clouds - cumulus cell
> Sea breeze
> Monsoon - India and Arizona
> Global circulation
Effect of convection on flames - Left image (with gravity, i.e., convection)
Right image (low gravity in space, i.e., little convection)
http://microgravity.grc.nasa.gov/combustion/cfm/cfm_index.htm
Factoid -
An oil lamp with a hollow wick burns 10 times brighter than a lamp with a solid wick
Climate and Global Change Notes
4-11
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Radiation
- Transfer without requiring a medium; vacuum; Electromagnetic waves
- All objects with temperature above absolute zero emit radiation
- The analogy of waves is often used to describe radiation
Height
Crest
Trough
Wavelength
Amplitude
Climate and Global Change Notes
4-12
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Radiation (Con’t)
- The analogy of waves is often used to describe radiation
> Wave Equation
‡ Example: Boat dock
‡ Speed of wave = wavelength * frequency
or
frequency = Speed of wave / wavelength
where ( Speed of wave ) for radiation is the speed of light which equals 3 x 108 m / s
Frequency Units -
RPM - Revolutions / minute
Hertz - cycles / sec
Climate and Global Change Notes
4-13
“He recognized the model, and knew it was a state-of-the-art microwave protection system. Mounted on each sturdy pole beneath an aluminum hood was a dieletric transmitter and a receiver; a 15 GHz signal was set to one of several selectable AM signal patterns.”
Ludlum, Robert, 2002: The Janson Directive. p. 449.
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)• Radiation (Con’t)
- Radiation from materials is emitted with a range of wavelengths, i.e., a spectrum of wavelengths
10 -14
10 -10
1
10 6
10 23
10 18
10 14
10 10
10 6
10 2
1
10 2
Frequency (hertz)
Wavelength(m)
GammaRays
Ultraviolet
Infrared
Microwaves
Short-wave
10 -2
10 -6
X Rays
Visible
TV
Broadcast Band TV - FM
Long - WaveRadio
NOTE:
GHz = gigahertz = 109 Hz
Climate and Global Change Notes
4-14
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Radiation (Con’t)
- Visible range from 0.4 to 0.7 microns
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http://observe.arc.nasa.gov/nasa/education/reference/reflect/ir.html
NOTE:
10-6 m = m= micron
Climate and Global Change Notes
4-15
Heat - Energy Transfer (Con’t)
Why is a red shirt red?
Why is a white shirt white?
Why is a black shirt black?
Why is a red flame red?
Why is a blue flame blue?
Climate and Global Change Notes
4-16
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Compare these two statements. Are they correct physics?
“The music was so loud, it was almost like no sound, like silence, in the same way that black is every color intensified into nothing.”
“K” is For Killer - Sue Grafton (p. 251)
“ ‘All colors taken together congeal to whiteness, the greatest part of space is black,’ say the journal notes.”
Golf in the Kingdom - Michael Murphy (p. 130)
Climate and Global Change Notes
4-17
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Radiation (Con’t)
- Ultraviolet (uv) C -Shortest wavelength; Most powerful; Filtered by the ozone layer
- uv B - Midrange uv; Less powerful; Produces both suntans and burns; Energy dissipated in outer layer of skin; Causes painful burns; Contributes to skin cancer; Do not penetrate glass
- uv A - Longer wavelength uv; Penetrates deeply into skin; causeslongterm damage; Causes premature aging; Adds to harmful effects of uv B; Can penetrate glass
Frequency (hertz)
Wavelength (m)
10-9
1018
1014
1013
Ultraviolet
10-5
10-6
Visible
0.20
0.320.29
uv C
uv B
uv A
ExpandedUltravioletWavelengths
Wavelength
(10 m)-6
0.40
Climate and Global Change Notes
4-18
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Radiation (Con’t)
- Radiation from materials is emitted with a range of wavelengths, i.e., a spectrum of wavelengths (Con’t)
10 20 30 40 50 60 70 80 90 1000
246
8
101214
16
1820
Exam Scores
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Climate and Global Change Notes
4-19
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Radiation (Con’t)
- What is the Sun’s spectrum?> Below is the Sun’s emitted radiation spectrum; assumes the Sun’s
outer surface temperature is 6000 K
Note: The Sun emits much of it’s radiation in the visible range with its wavelength of maximum emission, (max), is about 0.48 m, i.e., in the blue-green range
17,500
15,000
12,500
10,000
7,500
5,000
2,500
0 0.5 1.0 1.5 2.00.0
max
Wavelength (m)
Em
itte
d R
ad
iati
on
Per
Wav
ele
ng
th I
nte
rva
l(C
al -
cm
-2 -
min
- m
m -1
)
Visible Note: 1 calorie = energy required to heat 1 gm of water 1°C
Note: 1 Calorie (capital C; Unit used for food derived energy) = 1000 calories (lower case c) = 1 kilocalorie
95% of the Sun’s emitted radiation is in the region between 0.25 and 2.5 m
Climate and Global Change Notes
4-20
Heat - Energy Transfer (Con’t)
Three Mechanisms (Con’t)
• Radiation (Con’t)
- What is the Earth’s spectrum?> Below is the Earth’s emitted radiation spectrum; assumes the
Earth’s surface temperature is 288 K
Note: The Earth’s wavelength of maximum emission, (max), is about 9.8 m
95% of the Earth’s emitted radiation (gray area) is in the region between 2.5 and 25 m, i.e., at much longer wavelengths
0 10 20 300
0.025
0.050
Wavelength (m)
max
Em
itte
d R
ad
iati
on
Per
Wa
vele
ng
th I
nte
rval
(Cal
- c
m-2
- m
in -
mm
-1 )
Note: Energy amounts per wavelength interval much smaller than for the Sun
Climate and Global Change Notes
4-21
Heat - Energy Transfer (Con’t)
Stefan-Boltzmann Law
• The Total Radiation per unit area is directly proportional to the object’s absolute temperature to the fourth power, i.e.,
R = (Const) * T4 = (Const) * ( T * T * T * T )
where T is the temperature in Kelvin and the constant equals 5.67 x 10-8 watts / ( m2 K4 ).
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Ludwig Boltzmann 1844-1906http://www-groups.dcs.st-and.ac.uk/
~history//Mathematicians/Boltzmann.html
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Josef Stefan 1835-1893http://www-groups.dcs.st-and.ac.uk/~history//Mathematicians/Stefan_Josef.html
Climate and Global Change Notes
4-22
Heat - Energy Transfer (Con’t)
Stefan-Boltzmann Law
• Examples:
- For the Sun: T = 6000K
R(Sun) = 5.67 x 10-8 W / (m2 K4 ) * ( 6000K )4
= 7.35 x 107 W / m2
- For the Earth: T = 300K
R(Earth) = 5.67 x 10-8 W / (m2 K4 ) * ( 300K )4
= 4.6 x 102 W / m2
Climate and Global Change Notes
4-23
Heat - Energy Transfer (Con’t)
Wien's Displacement Law
• Wavelength of the maximum energy times the object’s temperature equals a constant
max* T = Const
where max is the wavelength of maximum energy, T is temperature in Kelvin and the constant equals 2.89 x 10-3 meter Kelvin.
Wilhelm Wien 1864-1928http://www-gap.dcs.st-and.ac.uk/~history/PictDisplay/Wien.html
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Climate and Global Change Notes
4-24
Heat - Energy Transfer (Con’t)
Wien's Displacement Law
• Examples:
- For the Sun: T = 6000K max (Sun) = Wavelength of maximum energy (Sun)
= ( 2.89 x 10-3 m K ) / ( 6000K ) = 0.48 x 10-6 m= 0.48 microns
- For the Earth: T = 300K
max(Earth) = ( 2.89 x 10-3 m K ) / ( 300K )= 9.6 microns
Climate and Global Change Notes
4-25
Heat - Energy Transfer (Con’t)
Summary
• Sun emits 1.6 x 105 more energy per area than the Earth emits
• The Sun’s energy spectrum is centered in the visible region while the Earth’s energy spectrum is centered in the infrared range
• 95% of the Sun’s radiation is in the region between 0.25 and 2.5 microns while 95% of the Earth’s radiation is in the region between 2.5 and 25 microns