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hey rc

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maihuna Legendary Member Default Avatar
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hey rc

Post Sun Sep 13, 2009 5:30 am
In 1975 Chinese survey teams
remeasured Mount Everest, the highest
of the Himalayan mountains. Like the
Line British in 1852, they used the age-old
(5) technique of “carrying in” sea level:
surveyors marched inland from the
coast for thousands of miles, stopping
at increments of as little as a few feet
to measure their elevation, and mark-
(10) ing each increment with two poles.
To measure the difference in elevation
between poles, surveyors used an
optical level-a telescope on a level
base-placed halfway between the
(15) poles. They sighted each pole, reading
off measurements that were then
used to calculate the change in elevation
over each increment. In sight of
the peaks the used theodolites-
(20) telescopes for measuring vertical and
horizontal angles-to determine the
elevation of the summit.
The Chinese, however, made
efforts to correct for the errors that
(25) had plagued the British. One source
of error is refraction, the bending of
light beams as they pass through air
layers of different temperature and
pressure. Because light traveling.
(30) down from a summit passes through
many such layers, a surveyor could
sight a mirage rather than the peak
itself. To reduce refraction errors, the
Chinese team carried in sea level to
(35) within five to twelve miles of Everest’s
summit, decreasing the amount of air
that light passed through on its way to
their theodolites. The Chinese also
launched weather balloons near their
(40) theodolites to measure atmospheric
temperature and pressure changes
to better estimate refraction errors.
Another hurdle is the peak’s shape.
When surveyors sight the summit.
(45) there is a risk they might not all
measure the same point. In 1975
the Chinese installed the first survey
beacon on Everest, a red reflector
visible through a theodolite for ten
(50) miles, as a reference point. One
more source of error is the unevenness
of sea level. The British
assumed that carrying in sea level
would extend an imaginary line from
(55) the shore along Earth’s curve to a
point beneath the Himalaya. In
reality, sea level varies according
to the irregular interior of the planet.
The Chinese used a gravity meter to
correct for local deviations in sea level.
-------------------------------------------------------------------------------------------------------
Q32
It can be inferred from the passage that
refraction would be most likely to cause
errors in measurements of a mountain’s
elevation under which of the following
conditions?
A. When there are local variations in sea
level
B. When light passes through humid air
C. When theodolites are used relatively far
from the mountain peak.
D. When weather balloons indicate low air
temperature and pressure.
E. When sea level has been carried in to
Within five to twelve miles of the summit.

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ballubalraj Senior | Next Rank: 100 Posts
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Post Mon Feb 15, 2010 7:15 pm
I will go with 'C'

To reduce the refration error, Chinese used their theodolites closer to the mountain. Hence, the error is more likely when the theodolites are far.

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ajith Legendary Member
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Post Fri Jan 29, 2010 1:09 pm
maihuna wrote:
Q32
It can be inferred from the passage that
refraction would be most likely to cause
errors in measurements of a mountain’s
elevation under which of the following
conditions?
A. When there are local variations in sea
level
B. When light passes through humid air
C. When theodolites are used relatively far
from the mountain peak.
D. When weather balloons indicate low air
temperature and pressure.
E. When sea level has been carried in to
Within five to twelve miles of the summit.
IMO C

refraction, the bending of light beams as they pass through air layers of different temperature and pressure
As the distance increases variation in pressure and temperature increases

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sanp_l Master | Next Rank: 500 Posts Default Avatar
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Post Sun Sep 13, 2009 1:16 pm
I feel Option D as an answer is direct.
Whats the OA?

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kiennguyen Senior | Next Rank: 100 Posts Default Avatar
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Post Wed Nov 04, 2009 11:40 pm
IMO B

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tanviet Legendary Member Default Avatar
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Post Mon Jan 11, 2010 9:10 pm
IMO C. I infer from " within 5 to 12 miles of thorodoir"

this is hard

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bln123 Senior | Next Rank: 100 Posts Default Avatar
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Post Tue Jan 12, 2010 2:07 am
My opinion is C

A -> not an issue
B -> type of air that would cause disturbance is not mentioned
D -> see B
E -> confuses info (see C)

C -> "To reduce refraction errors, the Chinese team carried in sea level to within five to twelve miles..." so they needed to get close to get a good measurement

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raisethebar Senior | Next Rank: 100 Posts Default Avatar
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Post Thu Jan 21, 2010 4:27 am
IMO C.
plz provide OA

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Post Thu Jan 28, 2010 10:39 pm
C for me too...

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gmatmachoman Legendary Member Default Avatar
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Post Fri Jan 29, 2010 2:14 am
bln123 wrote:
My opinion is C

A -> not an issue
B -> type of air that would cause disturbance is not mentioned
D -> see B
E -> confuses info (see C)

C -> "To reduce refraction errors, the Chinese team carried in sea level to within five to twelve miles..." so they needed to get close to get a good measurement
Fantastic inference bro
!!

IMO C

Maihuna is not there on the forum ...so OA may not be available..But my guess is C....

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bhavesh_09 Junior | Next Rank: 30 Posts Default Avatar
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Post Fri Jan 29, 2010 11:12 am
It should be B

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surfer123 Junior | Next Rank: 30 Posts Default Avatar
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Post Tue Nov 23, 2010 3:14 pm
I think it is c too. Where is this question from?

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mundasingh123 Legendary Member Default Avatar
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Post Tue Nov 23, 2010 10:04 pm
ballubalraj wrote:
I will go with 'C'

To reduce the refration error, Chinese used their theodolites closer to the mountain. Hence, the error is more likely when the theodolites are far.
Chinese team carried in sea level to
(35) within five to twelve miles of Everest’s
summit, decreasing the amount of air
that light passed through on its way to
their theodolites. The Chinese also
launched weather balloons near their
The telescopes were not brought closer to the peak, the sea level is brought closer.
Refraction occurs when light passes though different layers of air having different temperatures and pressures.
When light passes though humid air, temperature and pressure changes

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frank1 Legendary Member Default Avatar
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Post Thu Nov 25, 2010 3:41 am
Well
Down to B and C
I think B is what manhattan calls 'one word wrong'
I think word humid is nowhere in passage...
We will be using our external knowledge of subject if we think humid air has higher density and all....

and with c
down from a summit passes through many such layers


Larger distance means more layers...and higher chances of refrac errors
more over
what they do to correct them
make closer points...

so C sounds logical from most angles.

thanks

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mundasingh123 Legendary Member Default Avatar
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Post Thu Nov 25, 2010 3:53 am
frank1 wrote:
Well
Down to B and C
I think B is what manhattan calls 'one word wrong'
I think word humid is nowhere in passage...
We will be using our external knowledge of subject if we think humid air has higher density and all....

and with c
down from a summit passes through many such layers


Larger distance means more layers...and higher chances of refrac errors
more over
what they do to correct them
make closer points...

so C sounds logical from most angles.

thanks
Farther distance from the peak means more layers of air (with different temperature and pressure or same temperature and pressure ) ? we need to clarify this.When its already mentioned that refraction takes place due to temperature and pressure change , we know that humid air means temperature and pressure change .This makes use of info given in passage itself and no outside knowledge , does it?

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