Nokea
Which of the following is NOT a mode of heat transfer between a system and its surroundings?
- A. Conduction
- B. Convection
- C. Radiation
- D. Isothermalization
Correct Answer: A
Rationale: Isothermalization is not a mode of heat transfer. The three main modes of heat transfer are conduction (through direct contact), convection (through fluid motion), and radiation (through electromagnetic waves). In this question, choice A, conduction, is not a mode of heat transfer between a system and its surroundings. Conduction refers to heat transfer through direct contact between particles, without the movement of the particles themselves. Therefore, A is the correct answer. Choices B, C, and D are incorrect as they represent valid modes of heat transfer.
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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.
What is the purpose of a switch in a circuit?
- A. To reverse the direction of alternating current
- B. To increase the voltage of the battery or cell
- C. To increase the resistance of wires in the circuit
- D. To allow the circuit to open and close
Correct Answer: D
Rationale: The purpose of a switch in a circuit is to allow the circuit to open and close. When the switch is turned on, it provides a complete path for the current to flow through the circuit. When the switch is turned off, it breaks the circuit, stopping the flow of current. This function of opening and closing the circuit using a switch is essential for controlling the flow of electricity in various electrical devices and systems. Choices A, B, and C are incorrect because a switch does not reverse the direction of current, increase voltage, or increase resistance in a circuit; its primary function is to open and close the circuit.
Which of the following substances has the highest density?
- A. Mist
- B. Water
- C. Steam
- D. Ice
Correct Answer: B
Rationale: Water has the highest density among the options provided. Density is a measure of mass per unit volume. In this case, water in its liquid form is denser than mist, steam, and ice. Ice has a lower density than water because its crystalline structure causes it to be less dense. Mist and steam are forms of water vapor, which are much less dense than liquid water. Therefore, the correct answer is water (choice B).
What is the main difference between a reversible and irreversible process in thermodynamics?
- A. Reversible processes involve heat transfer, while irreversible processes do not.
- B. Reversible processes occur instantaneously, while irreversible processes take time.
- C. Reversible processes can be run in both directions with the same outcome, while irreversible processes cannot.
- D. Reversible processes violate the first law of thermodynamics.
Correct Answer: C
Rationale: A reversible process is an idealized process that can be reversed without leaving any change in either the system or the surroundings. In contrast, irreversible processes cannot be reversed and often involve entropy production or dissipation. Choice A is incorrect because both reversible and irreversible processes can involve heat transfer. Choice B is incorrect as the speed of a process does not determine its reversibility. Choice D is incorrect because reversible processes do not violate the first law of thermodynamics; they comply with it by maintaining a balance between energy inputs and outputs. Therefore, the correct answer is C, as it accurately captures the main difference between reversible and irreversible processes in thermodynamics.
Why doesn't a raindrop accelerate as it approaches the ground?
- A. Gravity pulls it down at a constant rate.
- B. Air resistance counteracts the gravitational force.
- C. Its mass decreases, decreasing its speed.
- D. Objects in motion decelerate over distance.
Correct Answer: B
Rationale: The correct answer is B. As a raindrop falls, it experiences air resistance which counteracts the gravitational force pulling it down. This balancing of forces prevents the raindrop from accelerating further as it approaches the ground. Choice A is incorrect because while gravity is pulling the raindrop down, air resistance opposes this force. Choice C is incorrect as the mass of the raindrop remains constant during its fall. Choice D is incorrect because objects in motion may decelerate due to various factors, but in this case, the focus is on why the raindrop doesn't accelerate.