JEE MAIN - Physics (2025 - 28th January Morning Shift - No. 5)
Consider following statements:
A. Surface tension arises due to extra energy of the molecules at the interior as compared to the molecules at the surface, of a liquid.
B. As the temperature of liquid rises, the coefficient of viscosity increases.
C. As the temperature of gas increases, the coefficient of viscosity increases
D. The onset of turbulence is determined by Reynold's number.
E. In a steady flow two stream lines never intersect.
Choose the correct answer from the options given below:
Explanation
(A) Surface tension arises due to the extra potential energy of the molecules at the surface of a liquid compared to the molecules in the interior.
(B) When a liquid is heated, the kinetic energy of it molecules increases, causing them to move more freely and overcome the intermolecular forces that contribute to viscosity, thus lowering it.
(C) Higher temperature in gas means faster moving molecules, resulting in more collisions and therefore an increase in viscosity.
(D) Reynold's number $$ = {{Inertial\,force} \over {Visous\,force}}$$
$${R_e} = {{\rho VD} \over \mu }$$,
v = velocity of flow
D = Diameter of pipe
If, $R_e < 2000$, flow is laminar flow
$2000 < R_e < 3000 \Rightarrow$ transition region
$R_e > 3000 \Rightarrow$ turbulant flow.
(E) Tangent at a point to the streamline gives the direction of net velocity of the flow. If the two streamlines intersect each other. It signifies two directions of velocity which cannot be possible. Thus, two streamlines cannot intersect each other. Hence, option 2 is correct.
Comments (0)
