Environmental Physics
Lecture 2
email: [email protected]
web: http://people.physics.anu.edu.au/~jps107/
Energy
Different kinds of energy
Potential
Chemical
Electric
Kinetic
Heat
Radiation
Mass
How much energy?
Light globe on for one hour
100W globe (incandescent)
25 W globe (compact flourescent)
Rice cooker
650 W, 45 mins
How much energy?
Car at 100km/h – kinetic energy
car = 1000 kg
Car travels 100km
8L petrol for 100km
Energy density of petrol approx. 45MJ/kg
1L petrol = .737 kg
How much energy?
Fusion reaction
2H
2H
+ 3H -> 4He + n + E
= 2.014 amu
3H = 3.016 amu
4He = 4.003 amu
n = 1.009 amu
1 amu = 1.66 × 10-27 kg
What is an atom?
Nucleus
Positively charged
Protons and neutrons
Electrons
In “clouds” around the nucleus
Same number as protons
Atom has no charge
Electron shells
Electrons have designated orbits – electron
shells
Shells fill up in order
How many electrons does
a carbon atom have?
What shells are they in?
Carbon atom
Outer shells are unfilled
Electrons can jump
between shells
Photons absorbed or
emitted
Electronic excitation
Energy levels
Electronic excitation can only happen at discrete
energies – energy levels
between around 25 eV and 1eV
or 50 nm and 1200 nm.
What is a molecule?
Two or more atoms joined together
O2, H2O, more...
Bonded together by some energy, energy is
required to break bonds
O2 – 5.2 eV, H2O – 4.82 eV, N2 – 9.8 eV
Also have electronic levels
Can also move in other ways
Vibration, rotation
Molecular energy levels
Electronic state energies
1 – 10 eV
1200 – 120 nm (IR to visible/UV)
Vibrational state energies
50 to 400 meV
25µm – 2480 nm (IR)
Rotational state energies
1 to 50 meV
1.2mm – 25 µm
What is a solid?
Array of atoms joined together
No longer has discrete energy states, but instead
has bands
Conduction band
Valence band
also has vibrational modes
phonons
The ozone layer
What is ozone?
O3
How is it formed?
O2 + hν (<240 nm) --> 2O
O + O2 --> O3
O3 + hν (310 – 200 nm) --> O2 + O
O3 + O- -> 2O2
Where is it? Why is it important?
The ozone layer
Absorption (arbitrary units)
The ozone layer
100
Ozone UV photon absorption spectrum
150
200
250
300
Wavelength (nm)
350
400
ChloroFlouroCarbons (CFCs)
Man-made chemicals
CFCl3 (Freon-11), CF2Cl2 (Freon-12)
Used in aircon, refrigerators, foam, solvents,
propellants
Long lifetime in atmosphere
CFCL3 – 45 yrs, CF2Cl2 – 100 years