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Kuwait University Faculty of Science Physics Department Modern Physics 209 First Midterm Examination Date: Name……………………………….. Student No. ………… 1. 2. 3. Solve all the given problems Show detailed solution for each problem Check the correct answer Prob. Marks 1 2 3 4 5 6 Total Phys 209 1. The maximum kinetic energy of the photoelectrons released from a metal surface when exposed to 492 nm light is 9.9 10-20 J. Energy drops to 3.8 10-20 J if the wavelength is changed to 579 nm. Use this data to calculate plank’s constant h and work function . 2. On e ) Show that W ein’s Law of max t = 0.201 hc/k can be derived from Plank’s Radiation Law ( ) Two) 8π hc 1 hc/kT 5 λ 1 e Using W ein’s Law calculate the temperature of a blue star. 3. A -ray of wavelength 0.01 nm collide with an electron at rest. If the ray is scattered through 180 by collision with an electron, calculate On e ) Two) 4. Wavelength of scattered -ray Kinetic energy and momentum of scattered electron Determine the angle for first order diffraction of thermal neutrons at room temperature scattered from NaCl crystal with inter plane separation 3 of 2.82 10-10 m. (At Room temperature the kinetic energy = kT ). 2 5. 6. A * particle has a rest energy of 1385 MeV and lifetime of 2 10-23 s. What is the typical result of measurement of its rest mass energy ? Show that group velocity and phase velocity are related by group phase λ d λ phase dλ