Physics 2B Exam 3
Name: _________________________________________
Rules: Work Alone. You may refer to our textbook, your notes and the online course materials ONLY.
Do your own work. Turn in this test along with the extra pages you may have for the long problems. You
can edit this document to give you more space to write your solutions so they fit on the exam. Make it neat
and complete!! Make it beautiful. I grade on neatness and completeness! Email me if you have any
questions. HAVE FUN! Due May 11th in lecture. Photocopy your exam to keep a copy to study with for
the final!!! Give me solutions you wish I’d give you!!! ;-)
Conceptual Questions Circle the Best Answer. (1 point each.)
1. A person spearfishing from a boat sees a stationary fish a few meters away in a direction about 30
degrees below the horizontal. To spear the fish (assuming it doesn’t change direction when it enters the
water), should the person aim
a) above where he sees the fish
b) precisely at the fish?
c) below the fish?
2. Light passes from a material with index of refraction 1.3 into one with index of refraction 1.2.
Compared to the incident ray, the refracted ray
A. bends toward the normal
B. is undeflected
C. bends away from the normal
3. Suppose the viewing screen in the figure is moved closer to the
double slit. What happens to the interference fringes?
A.
They get brighter but otherwise do not change.
B.
They get brighter and closer together.
C.
They get brighter and farther apart.
D.
They get out of focus.
E.
They fade out and disappear.
4. Car headlight reflected off the road is:
A. unpolarized
B. vertically polarized
C. horizontally polarized
5. Therefore, the polarization axes of Polaroid sunglasses is
D. unpolarized
E. vertically polarized
F. horizontally polarized
6.
Light produced by the sun is
a) polarized
b) unpolarized
7. Light produced by an incandescent light bulb is a) polarized
b) unpolarized
8. Which color bends more during refraction in glass?
a) red
b) blue
c ) green
9. Which color bends more through a diffraction slit?
a) red
b) blue
c ) green
10. Light of wavelength 1 illuminates a double slit, and interference fringes are observed on a screen.
When the wavelength is changed to 2, the fringes get closer together. How large is 2 relative to 1?
2 is larger than 1.
B)
2 is smaller than 1.
C) Not enough information to answer.
Long Problems. (30 pts each) Edit this handout to give enough room to solve the problems or use
additional paper and be generous with drawings!!
1. A narrow beam of white light enters a prism made of crown glass at 45.0 degrees incident angle as
shown.
A) At what angles do the red (660 nm) and violet (410 nm) components of the light emerge from the
prism relative the normal of the right side?
B) What is the angular deviation for the red and violet wavelengths?
The indices of refraction for red and violet light in
crown glass are 1.512 and 1.530, respectively.
Redraw the prism large enough to have room to
label rays and angles.
Justify your geometry!!
2. Light of wavelength 650.0 nm falls illuminates a double slit of slit spearation 0.255mm and forms
an interference pattern on a screen located 2.50 m behind the double slit. Sketch the situation and
include each part below and label everything carefully. Do NOT assume small angle
approximations.
a) Find the angle to the 3rd dark fringe above the center of the double slit.
b) Find the distance above the central bright maximum to the 3rd dark fringe.
c) Find the path difference for two waves traveling from each slit to the 3rd dark fringe.
d) Find the phase difference for two waves traveling from each slit to the 3rd dark fringe.
3. A hydrogen atom is in its 4th excited state (n=5). Using the Bohr model of the atom, calculate
a) the orbital speed, de Broglie wavelength, angular momentum kinetic energy and total energy of the
electron. Find the ionization energy of the 4th excited state.
b) Now the electron emits a photon and jumps down to the ground state. Recalculate all the parts in a)
for the electron and find the energy, wavelength and frequency of the emitted photon. What part of
the spectrum (visible, UV, X-Ray, etc) and which series is this photon from (Lyman, Balmer,
etc)?
c) Is energy conserved? Is angular momentum conserved? How did things change? Did the electron
speed up? Slow down? Discuss your results.
Show all your calculations and box your answers so that it is really easy to find and grade.