611. 1n an adjusted level, when the bubble is central, the axis of the bubble tube becomes parallel to
A. line of sight
B. line of collimation
C. axis of the telescope
D. None of these.

612. The imaginary line passing through the intersection of cross hairs and the optical centre of the objective, is known as
A. line of sight
B. line of collimation
C. axis of the telescope
D. none of these.

613. Cross hairs in surveying telescopes, are fitted
A. in the objective glass
B. at the centre of the telescope
C. at the optical centre of the eye piece
D. in front of the eye piece,

614. The real image of an object formed by the objective, must lie
A. in the plane of cross hairs
B. at the centre of the telescope
C. at the optical centre of the eye-piece
D. anywhere inside the telescope.

615. An internal focussing type surveying telescope, may be focussed by the movement of
A. objective glass of the telescope
B. convex-lens in the telescope
C. concave lens in the telescope
D. plano-convex lens in the telescope.

616. The tangent to the liquid surface in a level tube, is parallel to the axis of the level tube at
A. every point of the bubble
B. either end of the bubble
C. the mid-point of the bubble
D. no where.

617. The sensitiveness of a level tube decreases if
A. radius of curvature of its inner surface is increased
B. diameter of the tube is increased
C. length of the vapour bubble is increased
D. both viscosity and surface tension are increased.

618. In a constant level tube, size of the bubble remains constant because uppe ? wall is
A. of relatively larger radius
B. of relatively smaller radius
C. flat
D. convex downwards.

619. The line normal to the plumb line is known as
A. horizontal line
B. level line
C. datum line
D. vertical line.

620. In levelling operation,
A. The first sight on any change point is a back sight
B. The second sight on any change point is a fore sight
C. The line commences with a fore sight and closes with a back sight
D. The line commences with a back sight and closes with a foresight.

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