Nokea
Capillarity describes the tendency of fluids to rise or fall in narrow tubes. This phenomenon arises from the interplay of:
- A. Buoyancy and pressure differentials
- B. Density variations and compressibility of the fluid
- C. Viscous dissipation and inertial effects
- D. Surface tension at the liquid-gas interface and intermolecular forces
Correct Answer: D
Rationale: Capillarity occurs due to surface tension and intermolecular forces between the liquid and the walls of the narrow tube. These forces cause the liquid to rise or fall depending on the cohesion and adhesion properties. Surface tension at the liquid-gas interface and intermolecular forces are responsible for capillary action, making choice D the correct answer. Choices A, B, and C are incorrect as they do not directly relate to the specific forces involved in capillarity.
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When a junked car is compacted, which statement is true?
- A. Its mass increases.
- B. Its mass decreases.
- C. Its density increases.
- D. Its density decreases.
Correct Answer: C
Rationale: When a junked car is compacted, its volume decreases while its mass remains the same. As a result, the car's density increases because density is mass divided by volume. Choice A is incorrect because the mass of the car remains the same. Choice B is incorrect because the mass does not decrease. Choice D is incorrect because the density increases as the volume decreases, not decreases.
Sublimation is the change in matter from solid to gas or gas to solid without passing through a liquid phase. Outside of the laboratory, which solid provides the best example of this?
- A. Iron
- B. Silver
- C. Salt crystal
- D. Dry ice
Correct Answer: D
Rationale: Dry ice (solid carbon dioxide) provides the best example of sublimation outside of the laboratory. When dry ice is exposed to normal atmospheric conditions, it changes directly from a solid to a gas without passing through a liquid phase. This process is commonly observed in everyday situations such as creating 'smoke' or 'fog' effects. Choices A, B, and C (Iron, Silver, and Salt crystal) do not undergo sublimation. Iron and Silver melt and then vaporize, while Salt crystal dissolves in water, and the resulting solution evaporates, which involves a liquid phase.
A Carnot cycle is a theoretical ideal heat engine operating between two heat reservoirs at different temperatures. Which of the following statements is NOT true about a Carnot cycle?
- A. The efficiency of a Carnot cycle is solely dependent on the absolute temperatures of the hot and cold reservoirs.
- B. It is a reversible cycle, meaning the process can be run in both directions with the same efficiency.
- C. It operates isothermally at the hot and cold reservoir temperatures.
- D. It is the most efficient heat engine operating between the same two reservoir temperatures.
Correct Answer: C
Rationale: The statement that is NOT true is C. Although part of the Carnot cycle operates isothermally, not the entire cycle operates isothermally. The Carnot cycle consists of both isothermal and adiabatic processes. Choice A is incorrect because the efficiency of a Carnot cycle is indeed solely dependent on the absolute temperatures of the hot and cold reservoirs. Choice B is correct as a Carnot cycle is reversible, allowing the process to be run in both directions with the same efficiency. Choice D is also true as the Carnot cycle is the most efficient heat engine operating between the same two reservoir temperatures. Therefore, the correct answer is C.
Bernoulli's principle for an incompressible, inviscid fluid in steady flow states that the mechanical energy, consisting of:
- A. Pressure (P) only, remains constant along a streamline.
- B. Velocity (v) only, remains constant along a streamline.
- C. P + ½Ïv² (total mechanical energy), remains constant along a streamline
- D. Density (Ï) only, remains constant along a streamline.
Correct Answer: C
Rationale: Bernoulli's principle states that the sum of pressure energy (P), kinetic energy per unit volume (½Ïv²), and potential energy per unit volume remains constant along a streamline in an incompressible, inviscid fluid. This means the total mechanical energy of the fluid is conserved, making Choice C the correct answer. Choices A, B, and D are incorrect because Bernoulli's principle involves the conservation of the total mechanical energy, not just pressure, velocity, or density alone.
In terms of electrical conductivity, semiconductors fall between
- A. Conductors and insulators
- B. Conductors and superconductors
- C. Insulators and dielectrics
- D. Superconductors and insulators
Correct Answer: A
Rationale: Semiconductors have electrical conductivities that lie between those of conductors (high conductivity) and insulators (low conductivity). This positioning makes choice A, 'Conductors and insulators,' the correct answer. Choice B, 'Conductors and superconductors,' is incorrect because superconductors have perfect conductivity, not intermediate like semiconductors. Choice C, 'Insulators and dielectrics,' is incorrect because dielectrics are a type of insulator, so it doesn't show the progression from high to low conductivity. Choice D, 'Superconductors and insulators,' is incorrect because superconductors have the highest conductivity, opposite to the role of semiconductors.