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Surveying - Engineering

Q1:

Which of the following introduces an error of about 1 in 1000 if 20 m chain is used

A length of chain 20 mm wrong

B one end of the chain 0.9 m off the line

C one end of chain 0.9 m higher than the other

D middle of the chain 0.45 m off the line

E all the above.

ANS:E - all the above.

Slope Correction or error = h^2/2L.

Now we want to find the difference in height of chain ends for which 1 in 1000 or 20 mm in 20 m chain length will produce.

0.02 = h^2/(2 x 20),
h = 0.9 m,
So, option B along with A, C options is correct. Slope error= 20mm = h^2/2L.
Then, h=0.89m~0.9m.
i.e. one end is 0.9m higher/lower than another end. 1 in 1000 means 1000 m = 1m.
then 20 m = 1/1000* 20=20mm.