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1870 Dec F13 Review questions.pdf

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York University
Natural Science
NATS 1870
Robin Kingsburgh

TERM EXAM: SUNDAY DEC 15, 10am-12noon, TC Rexall Centre All topics since beginning of course More emphasis on topics post-midterm (65-70%) Mixed format: mult choice, short answer (more short answer than on midterm) OFFICE HOURS FOR EXAM: Thur Dec 12, 1:30-2:30pm, or by appointment REVIEW QUESTIONS: 1. WHAT’S THE DIFFERENCE BETWEEN FLUORESCENCE & PHOSPHORESCENCE? o when a UV source that is causing fluorescence is removed, a fluorescent objects stops glowing, and a phosphorescent one keeps glowing 2. Explain the process for fluorescence o 3 steps: o 1. UV photon is absorbed and an e- jumps to a higher level o 2. e- drops to slightly lower level, and no visible radiation is emitted o 3. e- returns to the lowest state, it emits a visible wavelength photon 3. What process involves luciferin& luciferase? o Bioluminescence: o How is bioluminescent emission produced?  chemical reaction involving luciferin, luciferase, and oxygen; this results in the luciferin being in an excited state (e- is in a high level); when the e- drops to a lower level, a photon is emitted -> that is bioluminescence (typically blue) o How does Green fluorescent protein in jellyfish produce green light?  protein absorbs the blue bioluminescent emission; fluorescence occurs, and the longer wavelength green light is emitted 4. Why do colourless substances absorb UV? o for the human eye to see a substance with colour, the substance needs to absorb in the 400-700nm range; when the absorption is in the UV, there is a large energy jump, and the substance is colorless 5. What sort of molecular structures commonly can absorb in this range and are present on colorants? o eg carotene family: conjugated bonds (alternating double and single bonds) o eg porphyrins – chlorophyll – extended ring structure, with a heavy metal in the middle o eg- adding atoms/ atom groups to molecules – Martius yellow 6. What are ionic and colvalent bonds? 7. Why does changing a molecule’s structure change the colour of the substance? o by changing the structure, the energy level spacing is changed o the wavelengths that the e- absorbs to jump energy levels changes o the remaining wavelengths change o the perceived colour changes 8. What is the law of reflection? o incoming angle = outgoing angle 9. Define specular and diffuse reflection 10.What is refraction? o the slowing down and bending of light as it moves from a less dense to a denser medium 11.What is total internal reflection? o when a light beam reflects at the interface of 2 mediums instead of refracting and exiting the medium (see diagram from notes) 12.What is scattering? o the redirection of a light beam by particles o Rayleigh: involves small particles that re-direct the shortest wavelengths  know why the sky is blue, and why sunsets are red o Mie: involves larger particles that re-direct all wavelengths – combine to white in
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