Kuwait University
Faculty of Science
Physics Department
Second Semester 2002-2003
Modern Physics 209
Final Examination
Date:
2002
Time: 12:30 - 14:00
Instructor: Dr. Hassan Raafat, Dr. Ali Rakhshani
Name……………………………….. Student No. …………
1.
2.
3.
4.
Solve all the given problems
Show detailed solution for each problem
Check the correct answer
Use the formula sheet.
Prob.
Marks
1
2
3
4
5
6
7
8
9
10
Total
1.
A spaceship approaches an observer from left and passes him to the
right with a constant speed. The light source of the spaceship appears to
the observer green (520 nm) in one situation and red a(650 nm) in the
other. W hat is the speed of the spaceship?
a ) 7 .9  1 0 6 m /s
2.
b ) 1 .5  1 0 5 m /s
c) 3 .1  1 0 8 m /s
d ) 3 . 9  1 0 7 m /s
A particle has a lifetime of 2 ns when it is at rest. How far can it travel
with a speed of 0.9 C in the laboratory frame?
a ) 0 .5 4 m
b ) 1 .0 8 m
c) 1.24 m
d ) 3 .7 2
3. A blackbody has a peak radiancy of R1 at 2500C and R2 at 4000C.
W hat is the ratio R2/R1 ?
a ) 1 0 .5
b ) 6 .6
c) 3.2
d ) 1 .6
4. An x-ray photon of wavelength 0.154 nm moves along the +x axis. It
undergoes scattering by a stationary electron. The electron gains 1%
of the incident photon energy. The scattered photon moves, with
respect to +x direction, at an angle of
a ) O
b) 69
c) 180
d) 55 
5. A beam of electrons accelerated through a potential difference of 80V
is incident perpendicularly on a metal surface that has an inter atomic
distance of 0.274 nm. At what angle, with respect to the metal surface,
the flux of diffraction electrons is maximum?
a) 60
b) 30
c) 45
d) 90 
6. The speed of the DeBroglie wave associated with a free proton is 1.1
C. W hat is the kinetic energy of this proton ?
a) 1.2 MeV
b) 940 MeV
c) 1.3 GeV
d ) 1 0 .2 Ge V
7. An electron beam produced by accelerating electrons through a
potential diffraction of 7V is incident on a barrier of 10 eV height and
0.2 nm thickness. The incident beam constitutes a current of 1 A.
Estimate the current associated with the tunneled electrons on the
other side of the barrier.
a)
b)
c)
d)
8. The wave function of a particle of mass m and energy E in the infinite
potential well shown below, is given as
Ψ (cx, t)  e -iωi (A e -ikx  B e -ikx ) where  = E/
1
and k = (2mE) 2 / .
On e )
Apply the boundary conditions and obtain the eigenvalues.
Two)
If the particle is electron and d = 0.2 nm, how much energy is
needed to excite the electron to its second excited state ?
a)
b)
c)
d)
9. Electromagnetic waves with certain wavelengths can be absorbed by
singly-ionized helium (E = 2) ions. W hat is the longest absorption
wavelength ?
a ) 3 0 .4 n m
10.
b ) 8 0 .5 n m
c) 120 nm
d( 20 0 nm
How much energy is required to transfer the electron in a hydrogen
atom from an orbit of radius 53 pm to another orbit with radius 477 pm ?
a ) 1 0 .2 e V
b ) 1 3 .6 e V
c) 12.1 eV
d) 0 E v
209 Test
1.
Nickel has a work function of 5.1 eV.
A ball of Nickel (work function, 5.1 eV) is suspended by an insulating
string in a vacuum chamber. It is illuminated with a UV light of
wavelength 200 nm.
On e )
W hat is the maximum speed of electrons expected from
nickel, as soon as the illumination begins?
Two)
W hat is the ultimate value for the electric potential that the ball
would acquire?
2.
An electron has been accelerated through a potential difference of
100 kV. W hat is the speed of the individual DeBroglie wave that forms
the wave packet associated with this electron?
a ) 3  1 0 8 m /s b ) 1 .6  1 0 8 m /s
c) 4.5  108 m/s
d ) 5 .6  1 0 8 m /s
3.
An electron is trapped in a one-dimensional infinite potential well,
extending from x = 0 to x = 0.2 nm. W hat is the probability of finding the
electron, that is in the 1st excited state, in the interval 0.05 < x < 0.1 nm ?
4.
A light beam of wavelength 800 nm can excite a simple harmonic
oscillator to its third excited state. W hat is the ground state angular
frequency of this oscillator ?