ConcepTest 6.4a
Parallel light rays cross interfaces
from air into two different media,
1 and 2, as shown in the figures
below. In which of the media is
the light traveling faster?
Refraction I
a) medium 1
b) medium 2
c) both the same
2
ConcepTest 6.4a
Parallel light rays cross interfaces
from air into two different media,
1 and 2, as shown in the figures
below. In which of the media is
the light traveling faster?
Refraction I
a) medium 1
b) medium 2
c) both the same
The greater the
difference in the speed
of light between the two
media, the greater the
bending of the light
2
2
rays.
Follow-up: How does the speed in air compare to that in 1 or 2?
ConcepTest 6.4b
Refraction II
Parallel light rays cross interfaces
a) n1 > n2 > n3
from medium 1 into medium 2 and
b) n3 > n2 > n1
then into medium 3. What can we say
c) n2 > n3 > n1
about the relative sizes of the index of
d) n1 > n3 > n2
refraction of these media?
e) none of the above
1
2
3
ConcepTest 6.4b
Refraction II
Parallel light rays cross interfaces
a) n1 > n2 > n3
from medium 1 into medium 2 and
b) n3 > n2 > n1
then into medium 3. What can we say
c) n2 > n3 > n1
about the relative sizes of the index of
d) n1 > n3 > n2
refraction of these media?
The rays are bent toward the normal
when crossing into #2, so n2 > n1.
But rays are bent away from the
normal when going into #3, so n3 < n2.
How to find the relationship between
#1 and #3? Ignore medium #2! So the
rays are bent away from the normal if
they would pass from #1 directly into
#3. Thus, we have: n2 > n1 > n3 .
e) none of the above
1
2
3
ConcepTest 6.5a
To shoot a fish with a gun,
should you aim directly at the
image, slightly above, or slightly
below?
Gone Fishin’ I
a) aim directly at the image
b) aim slightly above
c) aim slightly below
ConcepTest 6.5a
To shoot a fish with a gun,
should you aim directly at the
image, slightly above, or slightly
below?
Due to refraction, the image will
appear higher than the actual
fish, so you have to aim lower to
compensate.
Gone Fishin’ I
a) aim directly at the image
b) aim slightly above
c) aim slightly below
ConcepTest 6.5b
Gone Fishin’ II
To shoot a fish with a laser gun,
should you aim directly at the
a) aim directly at the image
image, slightly above, or slightly
b) aim slightly above
below?
c) aim slightly below
ConcepTest 6.5b
Gone Fishin’ II
To shoot a fish with a laser gun,
should you aim directly at the
a) aim directly at the image
image, slightly above, or slightly
b) aim slightly above
below?
c) aim slightly below
The light from the laser beam
will also bend when it hits the
air-water interface, so aim
directly at the fish.
ConcepTest 6.5 Heat Insulation
Imagine you are an alien from another planet with infrared eyes.
What do you see when you look around the room?
a) Bright spots where the bodies are and dark elsewhere.
b) Dark spots where the bodies are and bright elsewhere.
c) The same as what we see, only everything looks red.
d) The same as what we see, except that red is invisible.
ConcepTest 6.5 Heat Insulation
Imagine you are an alien from another planet with infrared eyes.
What do you see when you look around the room?
a) Bright spots where the bodies are and dark elsewhere.
b) Dark spots where the bodies are and bright elsewhere.
c) The same as what we see, only everything looks red.
d) The same as what we see, except that red is invisible.
Bodies are sources of heat and
therefore emit infrared radiation.
An alien with an instrument to
detect infrared would see these
sources as bright spots.
Infrared photo of a building to check
the heat insulation – where are the
problem spots in this case?
ConcepTest 6.6 Superman
Since Superman is from the planet
Krypton his eyes are sensitive to the
entire electromagnetic spectrum.
Does that mean he can use x-ray
vision to see that Lois Lane is being
kidnapped in the other room?
a) Yes, no problem
b) Nope, he can’t
c) Need more information
ConcepTest 6.6 Superman
Since Superman is from the planet
Krypton his eyes are sensitive to the
entire electromagnetic spectrum.
Does that mean he can use x-ray
vision to see that Lois Lane is being
a) Yes, no problem
b) Nope, he can’t
c) Need more information
kidnapped in the other room?
X-ray vision means that Superman’s eyes
can receive x-rays, but not send them!
So what would have to happen for him to
see Lois Lane being kidnapped?