# Surveying Questions and Answers – Levelling – Curvature and Refraction

This set of Surveying Multiple Choice Questions & Answers (MCQs) focuses on “Levelling – Curvature and Refraction”.

1. Horizontal line departs from a level surface because of _____________
a) Refraction
b) Radius of earth
c) Curvature of earth
d) Parallelism

Explanation: From the definition of level surface and a horizontal line it is evident that a horizontal line departs from a level surface because of the curvature of the earth.

2. In the long sights, the horizontal line of sight doesn’t remain straight but it slightly bends downwards having concavity towards earth due to ____________
a) Refraction
b) Radius of earth
c) Curvature of earth
d) Parallelism

Explanation: Due to refraction, in the long sights, the horizontal line of sight doesn’t remain straight but it slightly bends downwards having concavity towards earth.

3. Find the correction for curvature for a distance 1200 m?
a) 0.113 m
b) 0.131 m
c) 0.133 m
d) 0. 313 m

Explanation: Correction for curvature is 0.07849 d2. Therefore, here 0.07849*(1.2)2 = 0.113 m.

4. Find correction for refraction for a distance of 1200 m?
a) 0.0106 m
b) 0.0160 m
c) 0.0016 m
d) 0.0116 m

Explanation: Correction for refraction is correction for curvature/7.
Therefore, here (0.07849 * (1.2)2)/7 = 0.016 m.

5. Find the correction for curvature for a distance 2.48 km?
a) 0.483 m
b) 0.434 m
c) 0.443 m
d) 0. 403 m

Explanation: Correction for curvature is 0.07849 d2. Therefore, here 0.07849*(2.48)2 = 0.483 m.
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6. Find correction for refraction for a distance of 2.48 km?
a) 0.0066 m
b) 0.0160 m
c) 0.069 m
d) 0.096 m

Explanation: Correction for refraction is correction for curvature/7. Therefore, here (0.07849 * (2.48)2)/7 = 0.069 m.

7. Find combined correction for curvature and refraction for 3400 m?
a) 0.078 m
b) 0.778 m
c) 0.709 m
d) 0.786 m

Explanation: Combined correction for curvature and refraction is given by 0.06728 d2. Therefore, here 0.06728 (3.4)2 = 0.778 m.

8. Find combined correction for curvature and refraction for 1.29 km?
a) 0.112 m
b) 0.128 m
c) 0.212m
d) 0.221 m

Explanation: Combined correction for curvature and refraction is given by 0.06728 d2. Therefore, here, 0.06728(1.29)2 = 0.112 m.

9. In order to find the difference in elevation between two points P and Q, a level was set upon the line PQ, 30 m from P and 1280 m from Q. The reading obtained on staff kept at P and Q were respectively 0.545 m and 3.920 m. Find the true difference in elevation between P and Q?
a) 3.226 m
b) 3.343 m
c) 3.265 m
d) 3.345 m

Explanation: Since the distance of P from an instrument is small, the correction for curvature etc is negligible. Combined correction for Q is 0.06728 (1.28)2 = 0.110 m. Correct staff reading at Q = 3.920 – 0.110 = 3.810 m. Difference in elevation between P and Q = 3.810 – 0.545 = 3.265 m.

10. A light house is visible just above the horizon at a certain station at the sea level. The distance between the station and light house is 10 km. Find the height of the light house?
a) 0 6728 m
b) 0.06728 m
c) 67.280 m
d) 6.728 m

Explanation: Combined correction for curvature and refraction is given by 0.06728 d2. Therefore, here 0.06728 (10)2 = 6.728 m.

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