Consider following statements: Choose the correct answer from the options given below:
- B, C, D Only
- C, D, E Only
- A, D, E Only
- A, B, C Only
Answer
(2) C, D, E Only
Solution
A: Molecules at the surface have extra (potential) energy compared with those in the interior, because they have fewer neighbours attracting them. This extra surface energy per unit area is the surface tension. The statement reverses this. Incorrect.
B: Viscosity of a liquid decreases as its temperature rises. Incorrect.
C: Viscosity of a gas increases with temperature (faster molecules transfer more momentum between layers). Correct.
D: Turbulence sets in when the Reynolds number Re = v d exceeds a critical value (about 2000 for flow in a pipe). Correct.
E: The tangent to a streamline gives the velocity at that point; if two streamlines crossed, the fluid would have two velocities at one point, which is impossible. Correct.
C, D and E only are correct.
Answer: (2)