Physics MCQ Quiz
Explanation:
The correct answer is Increases.
Surface tension is caused by the cohesive forces between liquid molecules. As temperature decreases, the kinetic energy of molecules decreases, allowing intermolecular forces to become more significant. This results in an increase in surface tension.
The other options are incorrect because:
- Decreases: This would be true if temperature was increasing
- Remains constant: Surface tension is temperature-dependent
- First increases then decreases: No such pattern is observed
Explanation:
The correct answer is Shear strain, rate of shear strain.
For solids with elastic modulus of rigidity (like most solid materials), the shearing force is proportional to the shear strain (Hooke's Law). For fluids, the shearing force is proportional to the rate of shear strain (Newton's Law of Viscosity).
The other options are incorrect because:
- Shear strain, shear strain: Incorrect for fluids
- Rate of shear strain, shear strain: Reversed relationship
- Rate of shear strain, rate of shear strain: Incorrect for solids
Explanation:
The correct answer is Gases, liquids.
For gases, viscosity increases with temperature because higher temperatures increase molecular motion and momentum transfer between layers. For liquids, viscosity decreases with temperature because higher temperatures reduce the intermolecular forces that create viscosity.
The other options are incorrect because:
- Liquids, gases: Reversed relationship
- Both liquids, both gases: Doesn't account for the different behaviors
- Both gases, both liquids: Incorrect categorization
Explanation:
The correct answer is Greater.
For a scaled-down model in a wind tunnel, turbulence occurs at a greater speed than for the actual aircraft because the Reynolds number (which depends on characteristic length) is smaller for the model. To match the Reynolds number of the actual aircraft, the model would need to be tested at a higher velocity.
The other options are incorrect because:
- Lesser: Would be true if the model was larger than actual aircraft
- Equal: Only possible if model was same size as actual aircraft
- Sometimes greater, sometimes lesser: Not a consistent pattern
Explanation:
The correct answer is Conservation of mass, Bernoulli's principle.
The increase in flow speed at constrictions is due to conservation of mass (continuity equation) - the same mass flow rate must pass through a smaller area, requiring higher velocity. The decrease in pressure comes from Bernoulli's principle, which states that as velocity increases, pressure must decrease to conserve energy.
The other options are incorrect because:
- Bernoulli's principle, conservation of mass: Reversed relationship
- Both from Bernoulli's principle: Doesn't account for continuity
- Both from conservation of mass: Doesn't account for energy conservation
