Answer: (D)
Answer: (B)
CT-3. A two-slit interference pattern is viewed on
a screen. The position of a particular minimum
is marked. This spot on the screen is
further from the lower slit than from the top slit. How much further?
A) 2 l B) 1.5 l C)
3 l D) None of these
Answer: None of
these. The path difference is 2.5 l
As the technician
walks, she notes the tone from the radio is ...
A) very loud, all the time. B)
alternates loud and quiet as she walks.
C) very quiet, all the
time. D) quiet at first, and
then loud all the time
Answer: very quiet,
all the time. On the x-axis (to the
right of both), the more distant antenna is always 10.5 wavelengths further
than the closer antenna. So path difference is always 10.5 l, and the waves are always arriving at the
detector out of phase (destructive interference).
As the technician
walks, she notes the tone from the radio is ...
A) very loud, all the time. B) alternates loud and quiet as she
walks.
C) very quiet, all the
time. D)
quiet at first, and then loud all the time
Answer: very quiet
all the time. Although the path difference is zero, the two sources are emitting
out-of-phase, so the two waves arrive at the detector still out-of-phase:
destructive interference occurs always.
(We must assume that the technician does not get too close to the
antennas, so that the waves from the 2 antennas are moving in nearly the same
direction where the technician is.)
CT-6. A two-slit interference pattern is viewed on
a screen. The separation of the slits,
d, is slowly increased. What happens to
the pattern on the screen?
A) The fringes move
closer together. B) The
fringes move further apart.
C) There is no
change in the fringe separation. D) None
of these
Answer: The angular
separation of adjacent peaks is Dq = l /d . So as d
increases, Dq decreases, meaning the fringes move closer
together.
CT-7. A standard double-slit experiment is modified
by placing a small piece of glass in front the right slit (diagram below). The effect of the glass is to shift the phase
of the light from the right slit so that the two slits no longer emit
wavefronts in sync. Instead, the right slit emits a wavefront a little later
than the left slit.
After the glass is
inserted, the intensity pattern on the screen is...
A) unchanged B) shifts
to the right C) shifts left. D)
None of these.
Answer: the pattern
shifts to the right
CT-8. A standard double-slit experiment is modified
by placing a filter over one of the slits, which reduces the intensity of the
light from that slit by roughly a factor of 2.
After the one slit
is filtered, the new intensity pattern appears...
A) unchanged, same as before
D) None of these.
Answer: (B)
CT-9. Violet light of wavelength l passes through a single slit of width D and
forms a diffraction pattern on a screen.
If the violet light is replaced with red light of wavelength 2l, the original pattern on the screen is reproduced
if the slit width is changed to
A) D/2 B) D/4 C) 2D D) no change is necessary.
Answer: 2D. The angular width of the central max in a
single-slit diffraction pattern is Dq = 2l /D.
So if l doubles, D must be doubled to keep the ratio l/D constant.
CT-10. A
laser shines through a single slit and a diffraction pattern is seen on a
screen. Then a single thing about the
experiment is changed , so that the pattern looks
similar, but covers a smaller portion on the screen.
Select all
answers that could account for the smaller pattern.
1) The screen was
moved further away from the slit.
2) The wavelength of
the laser light was decreased.
3) The slit was
changed to a smaller width slit.
4) The laser was
moved closer to the slit.
A) 2 only B) all, 1234 C) No answer
is correct. D) 124
Answer: 2 only
s
A) Angle q is the same for both circles
B) Angle q is larger for the larger circle
C) Angle q is smaller for the larger circle
Answer: Angle q is the same for both circles
What is the phase
difference in radians?
A) 9p B)
18p C)
4.5p D) None of these
Answer: 9p One wavelength
corresponds to a 2p change in phase.
CT-13. A beam of white light shines thru a
diffraction grating, producing a rainbow spectrum. Which side of the spectrum is red?
A) The side furthest
from the central position
B) The side nearest
the central position.
Answer: The angle of the m=1 peak of light of
wavelength l is q = l/d. So larger wavelength means larger angle. The red light is
furthest from the central position.
CT-14. An aperture consists of an annular ring of
diameter d. The aperture is illuminated
with a plane wave. (The screen is far
away compared to d. ) Will there be a bright spot in
the middle of the screen?
Answer: (A) It is
called Poisson's bright spot.
A) d sinq B) d cosq C)
0 D) none of these
Answer: None of
these. The formula d sinq is the p.d. only in the special case that
the screen is very (infinitely) far away.
The correct formula for the path difference in this case is
CT-16. Two
slits, separated by a distance d = 0.15 m, are located a distance L = 850 mm
from a screen, in the usual double-slit geometry. The slits are illuminated by
a coherent plane wave of wavelength l = 600 nm.
A student is asked:
"What is the pathlength difference between the
two waves from the slits to the 1st minimum to one side of the
central maximum?
Is it possible to
answer this question immediately, without use of a calculator, or does the
student need to do a computation (such as the sine of some angle) to get the
answer?
A) Calculator not
necessary: can get answer by looking.
B) Calculator
necessary: almost no one can do that calculation in their head.
Answer: No
calculator necessary. The 1st minimum is where p.d. = l / 2 = 600/2 nm = 300 nm
CT-17. A laser beam shines through a diffraction grating and
forms a diffraction pattern on the screen, as shown. What is the orientation of the slits in the
grating?
Answer: The correct slit orientation is B.