2011 Chapter 3 Exam Practice problems

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Unformatted text preview: pts) A He‐Ne laser operates continuously and emits a beam of photons with energy 1.96 eV. What is the wavelength of the He‐Ne laser? d) (6 pts) What is the magnitude of the electric field in the beam emitted from a 5 mW He‐Ne laser? Assume the beam has uniform intensity across its circular cross‐section of 100 m diameter. 4 of 20 e) (4 pts) Excimer lasers are powerful gas lasers used for material modification and Lasik eye surgery that emit coherent light in pulses of duration ~20 ns. If a KrF excimer laser emits photons at =248 nm and the total energy in a pulse is 0.5 J, what is the number of photons emitted in a single pulse? f) (4 pts) If the work function of a certain metal is 3 eV, which of these two types of lasers (KrF and/or He‐Ne) can produce a photocurrent if they irradiated a cathode of this metal in a vacuum? g) (5 pts) Calculate the de Broglie wavelength of the electrons photoemitted from this metal cathode for the laser(s) in the answer to part f) above. 5 of 20 2009 Exam 1, Problem 3 – Blackbody Radiation A dual‐color infrared (IR) pyrometer is an instrument that measures temperature of an object remotely by measuring the intensity of IR radiation at two wavelengths and calculating the temperature from the ratio of intensities assuming that the object emits as a blackbody. The spectral irradiance I() (power per unit area per wavelength) of a real object can be approximated by: 2 1 where is the emissivity (0 < a) (6 pts) A dual‐color pyrometer measures the incoming radiation from an object at 1250 nm and 1600 nm. If the object is at 800 C, calculate the ratio of power at 1250 to power at 1600 nm. 6 of 20 b) (4 pts) Give one reason why is it better for a pyrometer to measure at two wavelengths rather than just one. (25 words or fewer) 7 of 20 2009 Exam 2, Problem 1 – Wavefunctions and Hydrogenic Atoms j) (5 pts) What is a wavefunction for an electron? What information does it give us? What are its units in 3D? (30 words or fewer) k) (1 pts) How many quantum numbers need to be given to fully specify t...
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