Test: Surface Tension, Capillarity, Vapour Pressure & Cavitation - Mechanical Engineering MCQ

Explanation: Capillarity rise or fall
h=4*cosθ*σ/ρ*g*d
=4*cos130*0.51/13600*9.81*0.007
=140 mm.

Explanation: d=4*cosθ*σ/ρ*g*h
=4*1*0.073/1000*9.81*0.005
=5.95mm.

Explanation: Power lost= torque * angular velocity
= force* radius* angular velocity
= shear stress * area* radius* angular velocity
Shear Stress = viscosity* velocity gradient
Power lost= 7916.8*3.142*0.3*0.3*0.3*2*3.142*60
= 25.31 kW.

Explanation: h=4*cosθ*σ/ρ*g*d
=4*cos147*0.25/6.5*1000*9.81*0.03
=-0.44 mm i.e 0.44 mm fall.

Explanation: Capillary rise is given by
h=4*cosθ*σ/ρ*g*d
hence rise is inversely proportional to g
In space g is 0 m/s2
Hence, capillarity rise will occur finitely and will be the whole length of tube.

Explanation: P=4*σ/d
d= 4*.51/500
=4.08 mm.

Explanation: For soap bubble,
P=8*σ/d
For liquid jet,
P=2*σ/d
Hence, soap bubble will be having more pressure difference.

Explanation: Capillary rise is given by
h=4*cosθ*σ/ρ*g*d
Inside the earth, g (acceleration due to gravity) decreases. Hence, capillary rise will increase compared to that on the earth’s surface.

Explanation: Capillary rise is given by
h=4*cosθ*σ/ρ*g*d
As temperature increases, σ(surface tension) decreases. Therefore, correspondingly rise(or fall) will decrease as their is direct proportional relation between the two.

Explanation: Rough surfaced pipes have more friction with the fluid and hence possibility of cavitation is more pronounced.