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Highway Engineering PYQ – TN TRB Lecturer

      

41. A bubble tube of a level has a sensitiveness of 20” per 2 mm division. Find the error in the reading on the staff held at a distance of 100 m from the level when the bubble is deflected by two divisions from the centre.

[TN TRB 2021: 2 Marks]

  1. 0.19 cm 
  2. 0.019 cm
  3. 0.19 m
  4. 0.019 m
Answer: Option D
Explanation:
Let,
S – Error (or difference) in staff intercept (in m)
n – Number of divisions travelled by air bubble
D – Horizontal distance between staff station & instrument station (in m)

Sensitivity of a bubble tube, α =

S

nD

x 206265 sec

⇒ 20 =

S

2 x 100

x 206265

⇒ S = 0.019 m

42. The distance between two stations was 1200 m when measured with a 20 m chain. The same distance when measured with a 30 m chain was found to be 1195 m. If the 20 m chain was 0.05 m too long, what was the error in the 30 m chain ?

[TN TRB 2021: 2 Marks]

  1. – 0.3 m
  2. + 0.3 m
  3. – 0.20 m
  4. + 0.20 m
Answer: Option D
Explanation:
Consider 20m chain,
Nominal length of chain, l1 = 20 m
Actual length of chain, l1‘ = 20.05 m
Measured length using 20m chain, L1’ = 1200 m

Thus, correct length between stations, L1 =

l1‘

l1

x L1’ =

20.05

20

x 1200

⇒ L1= 1203 m
Now, consider 30m chain,
Nominal length of chain, l2 = 30 m
Measured length using 30m chain, L2’ = 1195 m
Correct length between stations, L2 = 1203 m

⇒

l2‘

l2

x L2’ = 1203 m

⇒

l2‘

30

x 1195 = 1203

⇒ l2’ = 30.20 m
Hence, the 30 m long chain is 0.2 m too long. (i.e., +0.20 m)

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