Surface Tension

Step 1: Surface Area Analysis
When small droplets coalesce into a single large drop, the total surface area decreases.
Step 2: Energy Relation
Surface energy is proportional to surface area ( ).
Step 3: Conclusion
Since the surface area decreases, surface energy is released (liberated).
Final Answer: (B)

Step 1: Concept
Surface tension decreases with increasing temperature.
Step 2: Analysis
At the critical temperature, the interface between liquid and vapor disappears.
Step 3: Conclusion
Hence, surface tension becomes zero at the critical temperature.
Final Answer: (C)

Step 1: Einstein’s photoelectric equation: .

Step 2: For , .

Step 3: Increase in kinetic energy is not directly proportional due to work function .

Step 4: Since , new speed is less than .

Step 1: Understanding the Concept:
Capillary rise . So .
Step 2: Detailed Explanation:
(A) Jupiter has higher decreases -- TRUE
(B) Lift moving up with acceleration : effective decreases -- TRUE
(C) Moon has lower increases -- TRUE
(D) Lift moving down with acceleration : effective increases (not decreases) -- FALSE
Step 3: Final Answer:
Statement (D) is false; in a downward accelerating lift, capillary rise increases.

Step 1: Understanding the Concept:
Energy needed = increase in surface energy.
Step 2: Detailed Explanation:
Initial surface energy = . Final surface energy = . Energy needed = final - initial = .
Step 3: Final Answer:
The energy needed is .