exam 4 - Chem 115a Exam 4 Thursday November 12, 2009...

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1 Chem 115a E x a m 4 Print Name Last, First Thursday November 12, 2009 Last 3 digits SID # Professor Anna Krylov TA Name/Lab Time: Questions Points Score Grader 1 12 2 8 3 12 4 12 5 10 6 12 7 10 8 12 9 12 Total 100 INSTRUCTIONS 1. You must show your work to receive credit. 2. If necessary, please continue your solutions on the back of the preceding page (facing you). 3. YOU MUST Use black or blue ink. (No pencil, no whiteout.) 4. There are 8 problems on 8 pages. Please count them before you begin. Please Sign Below: I certify that I have observed all the rules of Academic Integrity while taking this examination. Signature
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2 1. (12 pts) (i) (4 pts) For a certain photoelectric cell, it is known that green light is able to eject electrons from the material used. Which of the following statements must be true? a) Red light will not be able to eject electrons from this photocell. b) Blue light will be able to eject more electrons than the green light. c) Blue light will be able to eject electrons from this photocell. d) All of the above are true. (ii) (4 pts) When heated to approximately 500 o C, a tungsten filament emits predominantly red light. When the same filament is heated to 1000 o C, which of the following must be true? a) The emission should shift to shorter wavelength light. b) The overall intensity of the emission should be higher. c) The emission should cover a wider spectrum of wavelengths of light. d) All of the above are true. (iii) (4 pts) If a student performs an endothermic reaction in a calorimeter, how does the calculated value of H differ from the actual value if the heat exchanged with the calorimeter is not taken into account? a) H calc would be more negative because the calorimeter always absorbs heat from the reaction. b) H calc would be less negative because the calorimeter would absorb heat from the reaction. c) H calc would be more positive because the reaction absorbs heat from the calorimeter. d)
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exam 4 - Chem 115a Exam 4 Thursday November 12, 2009...

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