Question

A bubble tube with divisions of 2 mm and a radius of 10 m has the sensitivity of about :

1. 40''
2. 80''
3. 2''
4. 20''
5.

Answer 1

Correct Answer - Option 1 : 40''

Explanation:

Senisitivity (α) is given by:

\({\rm{α }} = \frac{{\rm{S}}}{{\rm{D}}} = \frac{{{\rm{nl}}}}{{\rm{R}}}\)

Where,

S = difference between two staff readings, n = no. of divisions of bubble,

and α = sensitivity of bubble tube.

Now,

l = length of one division of bubble tube = 2 mm

R = Radius of bubble tube = 10 m = 10000 mm

∴ l/R = 1 × 2/10000 = 1/5000 

we know l/nR = S/nD = 1/5000

Sensitivity of bubble tube, \(α = \frac{S}{{nD}} \times 206265\;seconds\)

\(α = \frac{1}{{5000}} \times 206265\;seconds =41.2 sec\)

∴ Closest Option is Option (1)

The sensitivity of a level tube is the angle in seconds subtended at the centre by an arc of the level tube equal to one division of the tube.

The sensitivity of a bubble tube can be increased by –

1. Increasing the length of the level tube
2. Increasing the diameter of the tube
3. Increasing the internal radius of the level tube
4. Decreasing the viscosity of the liquid used in the tube
5. Decreasing the roughness of the walls of the level tube

Hence, The sensitivity of a level tube increases with an increase in the radius of curvature of the bubble tube and The smoothness of the finish of the inner surface of the bubble tube.

Sensitivity of bubble tube, \(α = \frac{S}{{nD}} \times 206265\;seconds\)

Where, s = staff intercept

n = no of divisions of bubble deviated

D = distance between staff and instrument station