GPHY 314 Chapter 3: Radiation and Energy Balance

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29 Dec 2020
CHAPTER 2: Radiation and Energy Balance
Temperature and Energy
Energy: capacity to do work, represented in unit of joule (J)
o 1J ~amount of energy needed to lift 100g about 1m
o Power: rate at which energy flows, usually expressed in watts (W)
1W = 1J/sec, so 60-W bulb consumes 60J of energy ever second
A gallon is a quantity i.e. gallon of water -> Akin to joule
o Rate at which water flows through pipe measured in gallons per minute
Rate at which energy flows is the power, measured in watts (J per s)
Internal energy: how fast the atoms and molecules in the object are moving
o If water molecules moving slowly in one glass, it has less internal energy than water
moving on other glass
o In solid, movements of atoms are approx. fixed in space by intermolecular forces
But atoms can still move small distances around their fixed position
Faster atoms move about their fixed position, the more internal energy
Temperature: measure of internal energy of an object
o As internal energy increases and molecules of object speed up, temperature of object also
o Kelvin scale: equal to temperature in degrees Celsius plus 273.15
Freezing temperate of 8°C is equal to 273.15K
Room temperature is ~22°C = 295K
Most temperatures found in Earth’s atmosphere between 200K and 300K,
average surface temperature ~288K
Preferred by physicists -> Temperature K proportional to internal energy
If temperature doubles from 200K to 400K, internal energy of object also
0K is absolute zero -> Temperature at which molecules have zero internal energy
and cease moving; coldest possible temperature
Electromagnetic Radiation
Energy transported from Sun to Earth by electromagnetic radiation (visible light, X-rays,
radio-frequency waves)
o Stream of photons: small discrete packages of energy
o As photons travel from point A to B, each carries small amount of energy
Photons have characteristic size referred to as wavelength, which determines how photos interact
with world
o Photons with wavelengths between 0.3-0.8 microns (millionth of a meter) can be seen
with the human eye -> Refer to as visible photons
In visible range, different wavelengths appear as different colours
0.4 = blue, 0.6 = yellow, 0.8 = red
o Photons with wavelengths from 0.8-1000 microns are beyond the red end of the visible
spectrum, invisible to humans -> Refer to as infrared photons
Play important role in Earth’s climate and our everyday lives
o Photons with wavelengths just below human detection limit of 0.3 are beyond the violet
end of the visible spectrum -> Refer to as ultraviolet photons
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