To identify an extensive property, we need to understand the definitions of extensive and intensive properties. Extensive properties depend on the amount of matter in a system, while intensive properties do not.
Correct Option: B) Heat capacity
The question asks about the Kelvin-Planck statement of the second law of thermodynamics. This law defines the limitations on converting heat into work in a cyclic process.
C) Conversion of heat into work — The Kelvin-Planck statement directly addresses the impossibility of a perfect conversion of heat into work in a cyclic process, highlighting the limitations of heat engines.
The question asks for the mechanism by which heat is conducted through liquids and gases. We need to recall how thermal energy is transferred at the molecular level in fluids and compare it with the conduction mechanisms in solids.
Identify the given information:
Recall the conduction mechanisms in solids:
In solids, heat is conducted by lattice vibrations (phonons) in all solids and, additionally, by the movement of free electrons in metals. Both mechanisms require a fixed crystal lattice or a sea of free electrons.
Recall the structure of liquids and gases:
In liquids and gases, the molecules are not held in a rigid lattice and are free to move randomly. There are also practically no free electrons available for carrying energy.
Identify the mechanism in fluids:
When one region of a fluid is hotter, its molecules move faster. These faster molecules collide with neighbouring slower molecules and transfer kinetic energy to them. Molecules also diffuse (migrate randomly) from hotter regions to cooler regions, carrying energy with them. Therefore, heat conduction in liquids and gases takes place through molecular collisions and diffusion.
Correct Option: C) Collisions and diffusion — In fluids, energy is passed on by collisions between randomly moving molecules and by their diffusion. Hence, Option C is the correct answer.
A) Lattice vibration: This is incorrect because lattice vibration is the conduction mechanism in solids, which have a fixed crystal lattice that liquids and gases do not possess.
B) Transportation of free electrons: This is incorrect because free-electron transport is the dominant conduction mechanism in metals, not in liquids and gases.
D) No heat conducted: This is incorrect because liquids and gases do conduct heat, although generally less effectively than solids.
Heat transfer is a fundamental concept in physics, describing the movement of thermal energy from one place to another. This movement is driven by a difference in temperature. Understanding the conditions necessary for heat transfer is crucial.
Correct Option: C) Temperatures of the two bodies must be different.
This is the essential condition for heat to be transferred from one body to another. Heat naturally flows from a region of higher temperature to a region of lower temperature. If there is no temperature difference, there is no driving force for heat transfer.
The question asks about the primary function of a silencer in an internal combustion engine. We need to identify which of the given options accurately describes its purpose or effect.
Correct Option: A) Reduces noise
The primary and most significant function of a silencer in an internal combustion engine is to reduce the loud noise produced by the expulsion of exhaust gases. It achieves this by dissipating the sound energy through various acoustic principles.
This question asks about the governing mechanism of diesel engines. Governing refers to the method by which the engine's power output and speed are controlled. Understanding the fundamental difference in fuel delivery between petrol (gasoline) and diesel engines is key to answering this.
A) Quality governed — Diesel engines control their power output by varying the amount of fuel injected into the combustion chamber, while the amount of air drawn in remains relatively constant. This method of controlling power by changing the fuel-to-air ratio (i.e., the "quality
The question asks for the theoretically correct (stoichiometric) air-fuel ratio for petrol (gasoline) in internal combustion engines. This ratio is crucial for complete combustion, maximizing efficiency, and minimizing emissions.
B) 15:1 — This is the widely accepted theoretical (stoichiometric) air-fuel ratio for complete combustion of petrol. While the exact value is closer to 14.7:1, 15:1 is the standard answer in most contexts.
The question asks about the primary application of the trepanning operation in machining. Trepanning is a specific machining process used for creating holes, and its suitability depends on the size of the hole required.
Correct Option: D) Producing large holes
The question asks about the shielding gases used in TIG (Tungsten Inert Gas) welding. TIG welding requires an inert atmosphere to protect the weld pool and tungsten electrode from atmospheric contamination. The choice of shielding gas is crucial for weld quality and process efficiency.
B) Argon and helium — Argon and helium are the primary inert gases used as shielding gases in TIG welding. They protect the weld area from atmospheric contamination, ensuring a high-quality weld.
The question asks about the use of cores in centrifugal casting. To answer this, one needs to understand the fundamental principle of centrifugal casting and how it forms hollow objects.
D) Cores are not used
In centrifugal casting, the centrifugal force itself forms the hollow section of the casting. The molten metal is flung outwards against the mold walls, and as it solidifies, it leaves a hollow interior. Therefore, there is no need for a physical core to create the internal cavity.