B.2 Greenhouse effectIB Physics HL: Flashcards

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Define albedo.

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Define albedo.: Total scattered power ÷ total incident power.
Define emissivity.: Power radiated per unit area ÷ σT⁴ (the black-body value at the same temperature).
Why does the Earth's albedo vary from day to day?: Cloud cover changes, and clouds are highly reflective.
Why does albedo vary with latitude?: Polar snow and ice reflect strongly; tropical oceans and forests absorb more.
What is the solar constant?: The intensity of solar radiation at the Earth's mean distance, perpendicular to the rays (≈ 1361 W m⁻²).
Why is the mean incoming intensity S/4?: The Earth intercepts sunlight over πR² but has surface area 4πR².
Write the equilibrium condition for a planet.: (1 − albedo) × S/4 = eσT⁴.
Name the four main greenhouse gases.: Methane, water vapour, carbon dioxide and nitrous oxide.
Give a human source of methane.: Livestock, rice paddies, landfill or gas leaks.
Why do greenhouse gases absorb infrared but not visible light?: Infrared photon energies match the gaps between their vibrational energy levels; visible photons do not.
Explain the resonance model of the greenhouse effect.: IR frequencies match the natural vibration frequencies of the molecules, so they resonate and absorb energy.
In which direction do greenhouse molecules re-emit infrared?: In all directions, so some returns to the surface.
Define the enhanced greenhouse effect.: The increase in the greenhouse effect caused by human activities raising greenhouse-gas concentrations.