Boundary layer separation is characterised by one of the conditions given below, where 'Re' is the Reynolds number for the flow. Select the appropriate conditions.

Velocity of liquid hydrocarbon fuels in a pipeline can not be measured by magnetic flowmeters, because their __________ is very low/small.

A. Thermal conductivity

B. Electrical conductivity

C. Specific gravity

D. Electrical resistivity

For turbulent fluid flow in pipe, the expression for Prandtl one seventh power law is (where, r = pipe radius, x = distance).

A. $$\frac{{\text{V}}}{{{{\text{V}}_{\max }}}} = {\left( {\frac{{\text{x}}}{{\text{r}}}} \right)^{\frac{1}{7}}}$$

B. $$\frac{{\text{V}}}{{{{\text{V}}_{\max }}}} = {\left( {\frac{{\text{r}}}{{\text{x}}}} \right)^{\frac{1}{7}}}$$

C. $$\frac{{\text{V}}}{{{{\text{V}}_{\max }}}} = {\left( {{\text{x}} \times {\text{r}}} \right)^{\frac{1}{7}}}$$

D. None of these

Capillary rise of mercury in a small diameter tube is proportional to (where, d = diameter of the tube, σ = surface tension of mercury)

A. d

B. $$\frac{1}{{\text{d}}}$$

C. $$\sigma $$

D. $$\frac{l}{\sigma }$$

What is the force required (in Newtons) to hold a spherical balloon stationary in water at a depth of H from the air-water iterface? The balloon is of radius 0.1 m and is filled with air.

A. $$\frac{{4\pi {\text{g}}}}{3}$$

B. $$\frac{{0.01\pi {\text{gH}}}}{4}$$

C. $$\frac{{0.01\pi {\text{gH}}}}{8}$$

D. $$\frac{{0.04\pi {\text{gH}}}}{3}$$