Download Phys 209BH

Kuwait University
Faculty of Science
Physics Department
Modern Physics 209
First Midterm Examination
Date:
Name……………………………….. Student No. …………
1.
2.
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Solve all the given problems
Show detailed solution for each problem
Check the correct answer
Prob.
Marks
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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