A projection manometer is to be used for measuring the dynamic pressur...
Solution:
Given:
Least count of manometer scale = 0.1 mm
Specific gravity of alcohol = 0.8
Formula:
Dynamic pressure = ½ * ρ * V²
Where, ρ = density of air
V = velocity of air
Conversion factor: 1 mm of alcohol column = 0.8 mm of water column
Calculation:
1. The dynamic pressure of the airstream can be measured by the projection manometer.
2. The least count of the manometer scale is given as 0.1 mm.
3. The manometric liquid used is alcohol of specific gravity 0.8.
4. The lowest velocity that can be measured is to be calculated.
5. Let us assume that the height of the manometeric liquid column is ‘h’ mm.
6. The density of alcohol can be calculated as follows:
Density of water = 1000 kg/m³
Density of alcohol = 0.8 * 1000 = 800 kg/m³
7. The pressure difference between the two arms of the manometer can be calculated as follows:
Pressure difference = ρ * g * h
Where, g = acceleration due to gravity = 9.81 m/s²
8. The pressure difference can be converted to dynamic pressure as follows:
Dynamic pressure = Pressure difference / 2
9. Substituting the values in the formula, we get:
Dynamic pressure = (800 * 9.81 * 0.1) / (2 * 1000) = 0.03924 Pa
10. Let us assume that the velocity of the airstream is ‘V’ m/s.
11. The dynamic pressure can be calculated as follows:
Dynamic pressure = ½ * ρ * V²
12. Equating the two dynamic pressures, we get:
0.03924 = ½ * ρ * V²
13. Substituting the value of density of air (ρ = 1.225 kg/m³), we get:
0.03924 = ½ * 1.225 * V²
14. Solving for V, we get:
V = √(0.03924 / (½ * 1.225)) = 2/√3 m/s
Therefore, the lowest velocity that can be measured is 2/√3 m/s.
Answer: (B) 2/√3 m/s
A projection manometer is to be used for measuring the dynamic pressur...
Ans : B