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LIGHT QUESTIONS and ANSWERS 1. What does it mean to say an atom is excited? An electron or electrons have more energy than their ground state, which is where they would be if they had not gained energy in some way. 2. How does the energy of the photon that is emitted by an electron jumping between two energy levels compare to the energy difference of the two energy levels? Exactly the same energy. 3. How is the energy of a photon related to its frequency? Higher energy means higher frequency: E = hf. 4. Which has the higher frequency, red or blue light? Which has the greater energy per photon, red or blue light? BLUE. 5. Why does the flame of a burning log have different colors in it? Different gases in the air have different emission spectra when excited, so the colors come from electrons jumping down from different energy levels in (possibly) different atoms. 6. When a gas glows, discrete colors are emitted. When a solid glows, the colors are smudged or continuous. Why? In the solid, the atoms are all connected to each other and the individual electrons from different atoms are interacting with each other in ways that prevent them from having distinct energy levels like we saw in gases. 7. How does an absorption spectrum differ in appearance from an emission spectrum? The absorption spectrum has dark lines which indicate which color photons were absorbed by the gas and able to excite photons up to higher levels. There are always less dark absorption lines than bright emission lines because the electrons can jump down to the ground state after being excited in many ways but can only jump up to a level from the ground state in one way. 8. How can astrophysicists tell whether a star is receding or approaching Earth?
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This note was uploaded on 02/10/2011 for the course PHYS 14 taught by Professor Physcs14 during the Spring '09 term at Santa Monica.

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