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Lecture 3

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University of Toronto St. George
Jon Abott

CHM310 – Lecture 3 –  There’s been water on the surface of the earth for most part of the history.  The earth is warm enough to keep the water from freezing.  How much the planet is going to change from greenhouse effect? 1) What keeps the planet warm? a) Sun i) Even though it doesn’t necessarily have to be the sun ii) If you go down below the surface of the earth its hot, but its not the sun which is the source of it 2) Types of radiations we should be concerned about a) The visible spectrum is the most part associated with the sun 3) Slide 1 – a) A plot of intensity visible 400-700nm -2 -1 b) Intensity Wm A c) Within 400 and 700 we see the most of the radiation d) What can happen when radiation comes into earth i) It can excite electrons/molecules (A) st ii) 1 possibility : The photons are absorbed  the molecule gets excited  it is an electron so it changes its electron configuration (excitation)  the excited molecule A reacts/ releases energy  or gets down to ground state with the help of a buffer gas who takes away the extra energy iii) Another possibility is A = metastasis – break apart into parts 4) h2 + A  A+h(mu) – The direction of the photon is changed, scattering 5) The classic example of scattering is the reason the sky is blue. If you look at the sun it is white, but if you look away from the sun it is blue. 6) The efficiency of scattering is inversely proportional to the wavelength. That is why we see blue. Blue  low wavelength, high energy | Red  high wavelength, low energy Photons getting scattered from the beam of light 7) If we got a cloudy sky, why does it look white? Protons going into it that it bounces many many times and there are so much collisions so they all gets scattered many many times we het white 8) The blue gets scattered out and what’s left over is red that’s why sometimes we see the sky as red in the morning near the sun 9) There are two processes which could happen when light interacts with matter a) Scattering / reflection b) absorption 10) irradiation curve at sea level: why is it lower? a) Visible molecule don’t absorb all that much, few do. b) If it’s not absorbed, then it is scattered c) Scattering occurs when the scatterer/ the molecule is much more smaller than the wavelength of the light. The wavelength of the light is very small. d) If you look at the earth from space you will notice that most of the visible light is being scattered. 11) So these are what makes us warm 12) Peripheral Black Bodies 13) Black body : therotical entity which absorbs every photon hitting it. The light it emits =light absorbed 14) Emission of a black body: Sun is a whole lot hotter than 5900 C. the outermost layer of the sun is called photosphere. 15) The shape of the black body curve is very similar to the amount of radiation hitting the top of the atmosphere arriving from the sun 16) The first order we can approximately amount as arriving at the sun = energy given by the sun 17) This energy gets into the earth’s orbit 18) Assuming that the sun is a black body, how much energy does it send to the atmosphere pf the earth? a) The energy given by the black body = sigma T (Stephan Boltzmann law) i) Total amount of energy the BB spits out, only depends on its temp
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