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UPSC Civil Service Exam Questions - Engineering

Q1:

A 3000 m long line lying at an elevation of 450 m measures 10 cm on a vertical photograph.
The focal length of the camera is 21 cm. The scale of the photograph for the area having an elevation of 1000 m will be

A 1 : 27381

B 1 : 25008

C 1 : 20606

D 1 : 30421

ANS:A - 1 : 27381

Scale = 10/(3000 *100) = 1/30000.
Now,
1/30000 = 0.21/(H - 450).
You get flying height, H = 6750m.

For 2nd case.
Scale = f/(H - h).
Scale = 0.21/(6750 - 1000) = 1 in 27381.