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Unformatted text preview: Quiz 4 Rubric Code: QQQQQQ Withheld Student ID:
DL Section #: 2 Last Name: I certify that I will abide by the UC Davis
Code of Academic Conduct Physics 7C Winter 2010 Martin First Name: Damien Signature: Lig m
ht Plopper the Pig is stranded in the desert. He thinks he sees a lake in the distance but, since he is a
smart pig, he knows it is only a mirage. What looks like a lake is actually the blue sky. The fact that it
looks like it is on the ground is an illusion created by refraction. Letʼs develop a simple model to
explain how mirages work.
of Note angle the same
(total internal reﬂection) sky Region 1 All normals
shown Region 2
Ground Apparent location of “lake” 1: It turns out that the index of refraction of air depends on the temperature of the air. In the picture above the
temperatures in each region go from cold in Region 1 to hot in Region 5. Mathematically: TRegion 1 < TRegion 2 <
TRegion 3 < TRegion 4 < TRegion 5. In order for the ray pictured to reach Plopperʼs eyes, rank the indices of
refraction for each region from the highest (slowest velocity of light) to the lowest (highest velocity of light).
Brieﬂy explain your decision. The light bends away from the normal as we go from region 1 to region 5.
Therefore the index of refraction is decreasing:
n_1 > n_2 > n_3 > n_4 < n_5
(Alternatively, just the T.I.R. between regions 4 & 5 tells me that region 5 must
have a smaller n than region 4)
2: Continue the ray from the patch of sky to Plopperʼs eyes in the illustration above showing how it bends at
each region boundary. Make sure to also draw the normal at the correct point at each boundary. (Hint: in order
for the “lake” to appear where it does in the illustration the ray needs to enter Plopperʼs eyes along the dotted
line. To do this, the ray needs to reﬂect at some point, and it canʼt reﬂect off the ground.) See ﬁgure 3: Plopper is nearsighted (he canʼt see objects far away very well) which is why he is wearing glasses in the
picture. What type of lenses, converging or diverging, are in his glasses to correct this problem? Describe
where the image needs to be formed; what sort of image it needs to be, and why the selected lens can do the
* The glasses need to create a virtual image between his near and far points.
(A real image would be on the "wrong side" and he could not focus on it)
* The far point is the issue. We need the virtual image to be closer than the object.
* Therefore the lens must be diverging (a virtual image from a converging lens is always further away
than the object) Image
(closer, virtual) Equations X F.P. Object ...
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This note was uploaded on 09/08/2010 for the course PHY7C 7C taught by Professor Neal/james during the Spring '10 term at UC Davis.
- Spring '10