Up: Old P120 Homework Questions
Previous: INTERFERENCE & DIFFRACTION
- 1.
- A certain fluid has a density of 0.8 g/cm3,
an index of refraction of 1.2 and is immiscible with water.
Suppose that 1 cm3 of this fluid is spilled into
a circular pool of water 2.2 m in diameter and spreads
evenly over the entire surface of the pool, which then calms
to a mirror-like smoothness.
You now kneel by the edge of the pool and look down at it
from a height of 50 cm. The pool is illuminated
with diffuse white light [all wavelengths coming from all directions].
- (a)
- What colour does the edge of the pool appear directly beneath you?
(Give the exact wavelength as well as a qualitative description.)
- (b)
- Draw a sketch of the appearance of the pool's surface
indicating the dominant wavelengths (colours) of the light
reflected from different (specified) regions.
Note: Don't forget about refraction.
- 2.
- In fairly bright light the pupil of your eye will contract
to a diameter of about 4 mm. Under these conditions,
assuming that you have ``perfect'' vision,
- (a)
- how far from your eye can you hold a book
and still be able to resolve two lines separated by
70 m
using green light with
nm?
- (b)
- Describe what you would see at this distance
when observing the same two lines with white light
(all wavelengths).
- 3.
- A laser operating at a wavelength of
0.6
m emits a beam which is a perfectly plane wave
(apart from diffraction effects) as it leaves the aperture of a
1.5
m diameter telescope coupled to the laser.
The beam is aimed at a
0.75
m diameter retro-reflector array
sitting on the surface of the Moon. The reflected pulse
is detected by the same Earth-based telescope
that emitted the original beam.
- (a)
- If the laser emits an average power of
20
mW [milliwatts], what is the average power
in the detected return signal?
- (b)
- How many photons per second does this represent
for the system described above?
Optional: The solar light flux in the vicinity of the Earth
is about
W/m2. If the Earth's albedo
(reflectivity) is 0.1, estimate the light flux reflected from the Earth
as it arrives at the Moon's surface: this ``Earthshine'' is what faintly
illuminates the Moon when it is ``new'' (i.e. dark) as seen from the Earth.
If the albedo of the Moon is 0.3 and our telescope looks at 1% of
the lunar hemisphere when seeking the laser signal, how much light
(in watts) does it intercept from the Earthshine-lit Moon?
How does this compare with the intensity of the returning laser signal?
- 4.
- An x-ray beam of wavelength
1
Å [Angstroms -- 1 Å
m]
is incident upon a crystal as shown below
(viewed ``end-on'' along an orthogonal symmetry axis).
At what angle
will the beam undergo
its first reflection maximum
from the indicated ``[3,1,0]'' planes?
Up: Old P120 Homework Questions
Previous: INTERFERENCE & DIFFRACTION