Question

Given below are two statements:
Statement (I): The axis of the bubble tube should be perpendicular to the vertical axis in dumpy level.
Statement (II): The line of collimation of the telescope of the dumpy level should be perpendicular to the axis of the bubble tube.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Check which axis should be perpendicular and which should be parallel to the line of collimation.

Answer 1

The Correct Option is C

Step 1: A dumpy level needs two permanent adjustments so that it gives a correct horizontal line of sight.
Step 2: The first adjustment requires the axis of the bubble tube to be perpendicular to the vertical axis of the instrument, so that the bubble stays centred while the telescope is swung all around, matching Statement (I), which is correct.
Step 3: The second adjustment requires the line of collimation to be parallel to the axis of the bubble tube, not perpendicular to it, so that the line of sight is horizontal whenever the bubble is centred. Statement (II) says this relation is perpendicular, which is wrong.
So Statement (I) is correct but Statement (II) is incorrect, which is option 3.