Question 1

In the context of simple machines, an axe used for cutting wood is mainly an example of which type of simple machine?

Accepted Answer

Introduction / Context: Simple machines are basic mechanical devices that help us do work more easily by changing the magnitude or direction of an applied force. Common simple machines include levers, wedges, screws, inclined planes, pulleys, and wheel and axle systems. Everyday tools such as axes, knives, and chisels are based on one or more of these basic ideas. This question asks you to identify the main simple machine principle behind an axe used for splitting or cutting wood. Given Data / Assumptions: The tool considered is a common axe with a sharp blade and a handle. The axe is used to cut or split wood by striking it. We need to classify it according to the standard types of simple machines. We focus on the blade shape and force action, not the handle grip alone. Concept / Approach: A wedge is a simple machine that consists of two inclined planes placed back to back. It converts an applied force on its blunt end into forces that act sideways and separate material at the sharp edge. The blade of an axe has a triangular cross section, essentially functioning as a wedge. When the axe is driven into wood, the wedge shaped blade forces the wood fibers apart. Although the handle might give some lever like advantage, the primary simple machine embodied in the axe head is the wedge. Step-by-Step Solution: Step 1: Observe the shape of the axe head. It is thicker at the back and narrows to a sharp cutting edge, forming a wedge shape. Step 2: When a person swings the axe, the kinetic energy and force are directed into the wedge shaped blade. Step 3: As the blade penetrates the wood, the sloping surfaces of the wedge push the wood apart, increasing the splitting force compared to the applied force. Step 4: This is exactly how a wedge operates, converting a force applied along its length into forces perpendicular to its surfaces. Step 5: Therefore, in simple machine classification, an axe is mainly considered a wedge. Verification / Alternative check: Textbooks that introduce simple machines often list axes, knives, chisels, and nails as familiar examples of wedges. They emphasise that any device with a sharp edge created by two sloping surfaces is a wedge. While the handle can be analysed as a lever in detailed mechanics, the question usually focuses on the primary function of the cutting edge, which supports the classification as a wedge. Why Other Options Are Wrong: Lever: The swinging motion uses the arm as a lever, but the axe head itself acts as a wedge during cutting. Screw: A screw is an inclined plane wrapped around a cylinder, which does not match the geometry of an axe blade. Inclined plane: A wedge can be thought of as two inclined planes together, but the specific simple machine for cutting tools like axes is the wedge, not a single stationary inclined plane. Common Pitfalls: Some learners choose lever because they concentrate on the handle and human arm movement instead of the cutting action. Others may confuse different simple machines that share similar principles. A good strategy is to focus on how the tool actually interacts with the material being worked on. For an axe, the spread of the blade inside the wood is the key, which is characteristic of a wedge. Final Answer: An axe used for cutting wood is mainly an example of a wedge as a simple machine.

Question 2

In electricity and magnetism, the quantity ampere second (A·s) is the unit of which physical quantity?

Accepted Answer

Introduction / Context: In basic electrical science, many derived units are formed by combining base units like ampere, second, metre, and volt. Understanding what each combination represents helps in interpreting formulas and circuit calculations correctly. The product ampere second (A·s) appears often when relating current and time. This question asks which physical quantity has ampere second as its unit in the SI system. Given Data / Assumptions: The unit considered is ampere multiplied by second, written as A·s. We assume standard SI definitions. Possible physical quantities listed include power, energy, conductance, and electric charge. We recall the basic relationships between current, charge, and time. Concept / Approach: Electric current is defined as the rate of flow of electric charge through a conductor. Mathematically, current I equals charge Q divided by time t, or I = Q / t. Rearranging this gives Q = I * t. If current is measured in amperes (A) and time in seconds (s), then Q is measured in ampere seconds, which is equal to coulombs (C). Therefore, ampere second is the unit of electric charge. Power, energy, and conductance have different unit combinations and do not match A·s. Step-by-Step Solution: Step 1: Recall the definition of current: I = Q / t, where Q is electric charge and t is time. Step 2: Rearrange this expression to obtain Q = I * t. Step 3: Note that in SI, current I is measured in amperes (A) and time t in seconds (s). Step 4: Substitute units into Q = I * t to get units of Q as A * s, which is ampere second. Step 5: Recognise that one ampere second is equal to one coulomb, the standard SI unit of electric charge, so ampere second represents charge. Verification / Alternative check: Check other quantities. Power P is defined as energy per unit time, and in SI its unit is watt, where 1 watt = 1 joule per second. Energy has units of joules, which can be expressed as volt coulomb or newton metre, but not simple ampere second. Conductance is the reciprocal of resistance and has SI unit siemens, which is ampere per volt. None of these match A·s. This confirms that ampere second is associated with electric charge only. Why Other Options Are Wrong: Power: Its unit involves joules per second, not ampere second. Energy: Measured in joules, which correspond to newton metre or volt coulomb, not directly A·s. Electrical conductance: Measured in siemens (A/V) rather than ampere second. Common Pitfalls: Learners sometimes see ampere and immediately think of current, forgetting that ampere second arises when integrating current over time. Another confusion is between coulomb and volt, where coulomb measures amount of charge and volt measures potential difference. Keeping track of basic formula I = Q / t and its unit analysis helps avoid these errors and solidifies understanding of derived units. Final Answer: The quantity whose SI unit is ampere second is electric charge.

Question 3

The rate of flow of electric charge through a conductor is called electric current. This rate is measured in which SI unit?

Accepted Answer

Introduction / Context: Electric current is one of the fundamental concepts in circuits and electronics. It describes how much electric charge passes through a cross section of a conductor in a given time. Knowing the correct SI unit for current is essential when interpreting circuit diagrams, using ammeters, or applying Ohm law. This question asks which unit is used to measure the rate of flow of electric charge. Given Data / Assumptions: Electric current is defined as charge flowing per unit time. The symbol for current is I, for charge is Q, and for time is t. The options include ampere, coulomb, ampere per coulomb, and ampere coulomb. We assume standard SI definitions for electrical quantities. Concept / Approach: By definition, electric current I equals Q divided by t. In SI, the base unit for current is the ampere, which is one of the seven base units of the International System of Units. One ampere is defined as one coulomb of charge passing through a cross section in one second. Coulomb represents the quantity of charge, not the rate. Combinations like ampere per coulomb or ampere coulomb are not standard physical units of basic quantities and are not used for current. Step-by-Step Solution: Step 1: Write the definition of current: I = Q / t, where Q is charge and t is time. Step 2: Recognise that the SI base unit for current is called the ampere, symbol A. Step 3: Note that one ampere corresponds to the flow of one coulomb of charge per second, so 1 A = 1 C / s. Step 4: Understand that coulomb by itself measures total charge, not the rate at which it flows. Step 5: Therefore, the rate of flow of charge, that is electric current, is measured in amperes. Verification / Alternative check: All circuit diagrams and electrical instruments label current in amperes or multiples like milliampere. Ammeters are calibrated in amperes, while voltmeters measure voltage in volts and energy meters in kilowatt hour. These practical conventions align with the theoretical definition that the SI unit of current is ampere. No instrument measures current directly in coulombs or in combinations like ampere coulomb in common practice. Why Other Options Are Wrong: Coulomb: This is the unit of electric charge, representing the quantity of charge, not its flow per second. Ampere per coulomb: This combination does not have a standard physical meaning for basic electrical quantities and is not used for current. Ampere coulomb: This product would represent a mixed unit with no simple interpretation as a basic electrical quantity. Common Pitfalls: Students sometimes confuse coulomb and ampere because they both appear in formulas about current. A useful memory aid is that coulomb measures “how much charge” there is, whereas ampere tells you “how fast the charge is flowing” through a conductor. Always associate current with rate and ampere, and charge with amount and coulomb. Final Answer: The rate of flow of electric charge, or electric current, is measured in ampere in the SI system.

Question 4

Which one of the following types of waves cannot propagate through vacuum and always requires a material medium for transmission?

Accepted Answer

Introduction / Context: Waves can be broadly classified into mechanical waves and electromagnetic waves. Mechanical waves require a material medium such as air, water, or solid matter for their propagation, while electromagnetic waves can travel through vacuum. Understanding this distinction is fundamental in physics and explains why we can receive sunlight from the Sun through empty space but cannot hear sounds from outer space. This question asks which listed wave cannot travel through vacuum. Given Data / Assumptions: We are comparing electromagnetic waves, light waves, sound waves, and heat radiation. Vacuum is a region with no matter, so no particles to vibrate. Mechanical waves need particle vibrations, but electromagnetic waves do not. Light and thermal infrared radiation are forms of electromagnetic waves. Concept / Approach: Sound waves are longitudinal mechanical waves resulting from pressure variations in a medium such as air or water. They rely on molecules colliding and transferring energy. Without molecules, as in vacuum, sound cannot propagate. Electromagnetic waves, including visible light and infrared radiation responsible for heat transfer by radiation, are oscillations of electric and magnetic fields and can propagate through vacuum at the speed of light. Therefore, among the options, sound waves are the only type that cannot travel through vacuum. Step-by-Step Solution: Step 1: Identify sound waves as mechanical pressure waves in a medium, requiring molecules or atoms to transmit disturbances. Step 2: Recognise that in vacuum there are no particles, so pressure variations cannot be transmitted and sound dies out. Step 3: Recall that electromagnetic waves such as radio waves, microwaves, infrared, visible light, ultraviolet, X rays, and gamma rays can all travel through vacuum. Step 4: Note that light waves and heat radiation are specific forms of electromagnetic waves, so they also propagate through vacuum. Step 5: Conclude that sound waves are the only listed waves that cannot propagate through vacuum. Verification / Alternative check: Astronauts in space rely on radios to communicate because sound cannot travel through the vacuum between spacecrafts. However, sunlight and thermal radiation reach Earth through the vacuum of space, demonstrating that electromagnetic waves do propagate without a medium. These observations match the theoretical classification and support the conclusion that sound waves need a material medium, while electromagnetic waves do not. Why Other Options Are Wrong: Electromagnetic waves: By definition, they can travel through vacuum at the speed of light. Light waves: Visible light is an electromagnetic wave that travels from the Sun through space to Earth. Heat radiation: Thermal infrared radiation from the Sun and other bodies reaches us through vacuum, so it does not require a material medium. Common Pitfalls: A common mistake is to assume that all waves need a medium because we experience sound in air. Another confusion arises between conduction, convection, and radiation as modes of heat transfer. Conduction and convection require matter, but radiation can occur through vacuum. Remember the simple rule: mechanical waves like sound need a medium, electromagnetic waves like light do not. Final Answer: The waves that cannot be transmitted through vacuum and always need a material medium are sound waves.

Question 5

Which of the following measurements depends on the value of the local gravitational field and therefore can change from place to place?

Accepted Answer

Introduction / Context: In mechanics, it is important to distinguish between mass and weight. Mass is an intrinsic property of matter, while weight is the gravitational force acting on that mass. This distinction explains why an object would "weigh" less on the Moon even though the amount of matter in it does not change. This question asks which measurement depends directly on the gravitational field strength and can vary from place to place. Given Data / Assumptions: Mass is the amount of matter in a body. Weight is the force due to gravity acting on that mass. Height is a geometric length measured along the vertical direction. Gravitational acceleration g can vary between planets and slightly on Earth. Concept / Approach: The weight W of a body is given by W = m * g, where m is mass and g is the local acceleration due to gravity. Mass does not depend on g and remains the same whether the object is on Earth, the Moon, or in space. Height is a length measurement and is not directly determined by gravitational acceleration, although gravity influences growth and structures in broader ways. Since weight is directly proportional to g, any change in g leads to a change in weight, making weight the measurement that depends on the local gravitational field. Step-by-Step Solution: Step 1: Write the formula for weight: W = m * g. Step 2: Note that mass m is an intrinsic property of the body and does not change with location. Step 3: Recognise that g is different on Earth, Moon, and other planets. For example, g on the Moon is about one sixth of that on Earth. Step 4: Since W depends on g, the same body has different weights at locations with different gravitational acceleration. Step 5: Height is measured as a length and does not have g in its definition, so it is not directly dependent on gravitational field strength. Verification / Alternative check: A person who has a weight of 600 newton on Earth will have a weight of about 100 newton on the Moon if mass is constant. Bathroom scales measure weight and give different readings when g changes. However, if you measure the mass of the same object using a balance that compares it with standard masses, the mass will be found unchanged. This practical observation confirms that weight depends on g, not mass or pure length. Why Other Options Are Wrong: Mass: It is independent of the gravitational field and remains constant for a body everywhere. Height: It is a measure of length and does not involve g in its basic definition. All of the above: This is incorrect because only weight directly depends on g among the listed quantities. Common Pitfalls: A frequent mistake is to use the words mass and weight interchangeably in daily language, which leads to confusion in physics. Another misconception is to think that a body "loses mass" on the Moon because the weighing scale reading changes. To avoid this, remember that mass measures quantity of matter, while weight measures gravitational force, and only weight involves the factor g explicitly. Final Answer: The measurement that depends on the value of the local gravitational field is weight.

Question 6

The depth of the ocean at a given location is commonly measured by which specialised oceanographic instrument?

Accepted Answer

Introduction / Context: Measuring the depth of oceans and seas is essential for navigation, laying submarine cables, studying marine life, and understanding the structure of the ocean floor. Special instruments and methods are used to determine how far the seabed is below the water surface. This question asks you to identify the instrument commonly used for depth measurement in oceanography. Given Data / Assumptions: We are interested in measuring vertical depth from the sea surface to the seabed. The instruments listed include anemometer, areometer, seismometer, and fathometer. Each of these instruments measures a different physical quantity in practice. We assume standard textbook definitions for these devices. Concept / Approach: A fathometer is a type of echo sounding device used to measure water depth. It sends sound pulses downward and measures the time taken for the echo to return from the seabed. Using the speed of sound in water, the instrument calculates the depth. An anemometer is used to measure wind speed, an areometer measures the relative density of liquids, and a seismometer records vibrations inside the Earth due to earthquakes. Only the fathometer is directly designed for ocean depth measurement. Step-by-Step Solution: Step 1: Recall that ocean depth is commonly determined by echo sounding, where sound waves travel to the bottom and reflect back. Step 2: The device that performs this function by generating and detecting sound pulses in water is called a fathometer. Step 3: Use the relation depth = (speed of sound in water * time taken for echo to return) / 2 to understand how the measurement works. Step 4: Recognise that an anemometer is a meteorological instrument used on land or at sea to measure wind speed, not depth. Step 5: Identify areometer as a device for measuring specific gravity of liquids, and seismometer as an instrument for recording seismic waves, neither of which is used for depth measurement. Verification / Alternative check: Marine charts and nautical maps often mention soundings taken by echo sounders or fathometers. Ships and submarines are equipped with depth sounding systems based on this principle. In contrast, wind reports from ships give readings in nautical knots measured by anemometers, and earthquake observatories use seismometers to record ground motion. This separation of roles among instruments confirms that the fathometer is associated with ocean depth. Why Other Options Are Wrong: Anemometer: Measures wind speed and sometimes wind direction, not water depth. Areometer: Used to measure relative density of liquids, such as in battery acid testing, not the depth of oceans. Seismometer: Records seismic vibrations inside the Earth due to earthquakes or explosions, not ocean depth. Common Pitfalls: Learners may mix up instrument names because many end with the suffix meter. A good strategy is to remember the root words: anemo relates to wind, hydro or phono often relate to water or sound, and seismo connects to earthquakes. The term fathometer comes from fathom, a unit of depth used in marine contexts, which hints clearly at its purpose. Final Answer: The depth of the ocean is commonly measured by a fathometer.

Question 7

In electronics and computing, analog synthesis refers to a technology based on which of the following principles?

Accepted Answer

Introduction / Context: In audio technology and electronic music, the terms analog and digital describe two different ways of representing and generating signals. Analog synthesis was widely used in early synthesizers and still has an important place in sound design. Understanding what makes a system analog helps in distinguishing it from digital sampling or purely numerical processing. This question focuses on the basic principle behind analog synthesis technology. Given Data / Assumptions: The context is synthesis of signals or sounds in electronics and computing. Four descriptions are given, some relating to digital sampling and some to analog representation. Analog systems use continuous physical quantities, while digital systems use discrete numbers. We are looking for the statement that best captures the analog principle. Concept / Approach: Analog synthesis involves generating and processing electrical signals that vary continuously in time and amplitude. These signals directly correspond to physical quantities such as voltage or current in circuits. In contrast, digital systems represent signals as sequences of numbers and operate using discrete steps. Sample based synthesis that stores brief digital recordings is a digital technique, even if controlled by a keyboard. Interfacing equipment is a general concept that does not define analog representation. Therefore, the correct description of analog synthesis is one that mentions representing data as measurable physical quantities that can vary in a continuous range. Step-by-Step Solution: Step 1: Recall that in analog electronics, information is carried by continuous signals, such as a voltage that can take any value within a range, not just fixed levels. Step 2: In analog synthesizers, oscillators, filters, and amplifiers shape electrical waveforms that correspond directly to the sound waves produced by speakers. Step 3: Recognise that placing short digital recordings under keyboard control is sample based digital synthesis, not analog synthesis. Step 4: Interfacing synthesizer equipment is related to connectivity and control but does not define the fundamental nature of analog representation. Step 5: Identify that representing data in terms of measurable physical quantities that vary continuously is the essence of analog technology, making this the correct option. Verification / Alternative check: Definitions of analog systems in standard electronics texts describe them as systems where signal variables are continuous in both time and amplitude and directly relate to the physical quantity being measured or generated. In contrast, digital systems are defined by discrete time and amplitude levels and representation using numbers. Sound synthesizers that use voltage controlled oscillators and filters are classic analog devices, matching the idea of continuous physical representations. Why Other Options Are Wrong: Placing short digital recordings under keyboard control: This is sample based digital synthesis, not analog synthesis. Interfacing multiple synthesizer devices: This is about connectivity and control, not how signals are represented internally. Representing physical quantities as discrete numbers only: This describes digital systems, not analog systems. Common Pitfalls: Students may think that any system related to music synthesis is analog if it uses knobs and keys, but the real difference lies in how signals are represented and processed. Another confusion is to equate analog with old and digital with new, which does not help conceptually. Always focus on continuity versus discreteness when deciding whether a system is analog or digital. Final Answer: Analog synthesis is based on representing data in terms of measurable physical quantities that vary continuously.

Question 8

In fluid mechanics, a Pitot tube inserted into a flow is primarily used to measure which quantity at the stagnation point?

Accepted Answer

Introduction / Context: Pitot tubes are widely used in aerodynamics, hydraulics, and industrial fluid systems to measure flow conditions. They can be seen on aircraft, inside pipelines, and in wind tunnels. The Pitot tube relies on converting the kinetic energy of the moving fluid into a pressure reading at a stagnation point. This question asks which specific pressure or quantity is measured directly by a Pitot tube inserted into a flow. Given Data / Assumptions: A Pitot tube is placed facing into the flow so that the fluid comes to rest at the tube opening. The fluid is assumed incompressible at moderate speeds for simplicity. Static pressure, dynamic pressure, and stagnation pressure are defined as in Bernoulli theory. We consider the basic form of a Pitot tube, not a combined Pitot static probe. Concept / Approach: When fluid enters the mouth of a Pitot tube that faces directly into the flow, it slows down and finally comes to rest at the stagnation point inside the tube. According to Bernoulli equation, the total pressure at this point is the sum of the static pressure and the dynamic pressure of the upstream flow. This total is called stagnation pressure or total pressure. The Pitot tube opening senses this stagnation pressure. Static pressure is usually measured separately by side ports, and dynamic pressure is then obtained as the difference between stagnation and static pressures. Step-by-Step Solution: Step 1: Recall that static pressure is the pressure felt by a fluid at rest or measured by a probe aligned parallel to flow without disturbing it significantly. Step 2: Dynamic pressure is given by (1/2) * rho * v^2, where rho is density and v is flow speed, and represents kinetic energy per unit volume. Step 3: Stagnation pressure equals static pressure plus dynamic pressure, and is the pressure at a point where the fluid velocity is brought to zero isentropically. Step 4: A Pitot tube facing the flow creates such a stagnation point at its entrance, so the pressure measured by the Pitot port is the stagnation pressure. Step 5: Dynamic pressure is calculated later by subtracting the separately measured static pressure from the Pitot stagnation pressure. Verification / Alternative check: Flow velocity in many practical setups is obtained by combining a Pitot tube with a static pressure tap, forming a Pitot static tube. The manometer connected between the stagnation port and the static port reads the difference, which equals dynamic pressure. That process confirms that the Pitot port itself measures stagnation pressure, not dynamic pressure directly. Aircraft airspeed indicators work in exactly this way. Why Other Options Are Wrong: Static pressure only: Static pressure is measured by separate static ports, not by the Pitot port itself. Velocity directly at the stagnation point: At the stagnation point the velocity is zero by definition, so velocity is not measured directly; it is calculated from pressures. Dynamic pressure directly: Dynamic pressure is obtained by subtracting static pressure from stagnation pressure, so it is not sensed directly by a single Pitot opening. Common Pitfalls: Students often confuse dynamic and stagnation pressure because both appear together in Bernoulli equation. It is helpful to remember that Pitot tubes stop the flow locally, so they must sense the combined effect of static and dynamic pressures, which is the stagnation pressure. Dynamic pressure is always a derived quantity, not something measured directly by a single simple port. Final Answer: A Pitot tube primarily measures the stagnation pressure (total pressure) of the flow at the stagnation point.

Question 9

In a standard engine lathe, the internal taper provided on the lathe spindle nose corresponds approximately to which taper ratio?

Accepted Answer

Introduction / Context: In manufacturing and machine tool technology, tapered holes and shafts are used to align and hold tools accurately. Engine lathes have a tapered hole in the spindle nose and tailstock to accept standard taper shanks for centres and tooling. This question asks about the approximate taper ratio provided on a typical lathe spindle, which is linked to a commonly used standard taper system. Given Data / Assumptions: The machine under consideration is a standard engine lathe used in workshops. The spindle nose has an internal taper to receive centres or tool holders. Several taper ratios like 1 in 10, 1 in 20, 1 in 15, and 1 in 25 are listed. We assume reference to common self holding tapers such as Morse taper. Concept / Approach: Morse taper is widely used in machine tools for holding drills, centres, and other tools. The approximate standard taper for Morse tapers is about 1 in 20, meaning that for every 20 units of length, the diameter changes by 1 unit. This gentle taper provides a good balance between self holding friction and easy removal. Lathe spindles and tailstock sockets typically use such a taper for proper alignment and torque transmission. Step-by-Step Solution: Step 1: Recall that Morse tapers are common in lathe spindle and tailstock design for holding centres and tool shanks. Step 2: The Morse taper system has a standard taper of approximately 1 in 20 for its self holding tapers. Step 3: A 1 in 10 taper would be much steeper and may not provide the same self holding characteristics suitable for general lathe spindle applications. Step 4: Ratios like 1 in 15 or 1 in 25 are not standard for Morse tapers and do not match the common workshop reference. Step 5: Therefore, the closest correct taper ratio for the lathe spindle is 1 in 20. Verification / Alternative check: Machine tool handbooks and engineering data tables list Morse taper specifications, with the taper per unit length corresponding approximately to 1 in 20. The slight variations in exact angles and diameters among different Morse sizes do not change the general approximation used in many examination questions. Since engine lathes almost universally use these standard tapers, this value is considered correct for general knowledge questions. Why Other Options Are Wrong: 1 in 10: This is a much steeper taper, more common in quick release or non self holding applications, and not typical of standard Morse taper spindles. 1 in 15: This does not match the widely accepted Morse taper approximation and is not the standard training value. 1 in 25: This is a milder taper than most self holding tapers used in spindles and is not the common reference value. Common Pitfalls: Learners may try to memorise many different taper ratios used in machine tools and then mix them up in exams. A practical strategy is to remember the approximate 1 in 20 value associated with Morse taper, since it appears frequently in lathe related questions. It is also helpful to distinguish self holding tapers like Morse from self releasing tapers used in milling machine spindles, which have different standard angles. Final Answer: The taper on a standard lathe spindle is approximately 1 in 20.

Question 10

What type of electromagnetic radiation is commonly used in the hand held remote control unit of a television set?

Accepted Answer

Introduction / Context: Television and other consumer appliances are often controlled from a distance using small hand held remote controls. These devices send signals wirelessly to the television, but the form of electromagnetic radiation used is not always obvious to users because the beam is invisible. This question tests your knowledge of which part of the electromagnetic spectrum is used in typical television remote controls. Given Data / Assumptions: We are dealing with common household television remote control units. The remote must transmit commands wirelessly over a short distance. The radiation is usually invisible to the human eye. Available choices are ultraviolet, visible light, infrared, and none of the above. Concept / Approach: Most television remotes use infrared light emitting diodes to send coded pulses to a receiver on the television. Infrared radiation lies just beyond the red end of the visible spectrum and is not visible to the human eye, but can be detected by suitable sensors. It is safe at the low power levels used and works reliably over the short distances found in living rooms. Ultraviolet radiation can be harmful at higher intensities, visible light would be distracting, and radio waves are more common in other wireless devices like Wi Fi and some advanced remotes. Step-by-Step Solution: Step 1: Recall that when you press a button on a remote, a small light emitting diode at the front of the remote flashes, though you may not see it with your eyes. Step 2: The invisible flashes are in the infrared region of the spectrum and are detected by a sensor on the television. Step 3: Ultraviolet radiation is higher in energy than visible light and is not commonly used for simple remote control links due to safety and design considerations. Step 4: Visible light could also carry information, but bright flashing lights from every key press would be inconvenient and easily disturbed by room lighting. Step 5: Therefore, the best match from the options for the radiation used in TV remotes is infrared radiation. Verification / Alternative check: If you point a television remote at a digital camera or smartphone camera and press a button, you can often see a faint blinking spot on the camera screen, because many digital sensors are sensitive to near infrared radiation. This simple experiment confirms that the remote is emitting infrared, not visible light. Technical specifications and diagrams in service manuals also describe remote control receivers as infrared sensor modules tuned to specific infrared wavelengths and modulation frequencies. Why Other Options Are Wrong: Ultraviolet radiation: Rarely used in consumer remotes because it can be harmful and is not needed for short range signalling. Visible light: Would be noticeable and distracting to users, and room lighting could interfere with the signal. None of the above: Incorrect, since infrared radiation is indeed the standard technology used. Common Pitfalls: Some learners might assume that because radio waves are widely used in wireless systems, TV remotes must also use radio frequencies. While some advanced remotes do use radio technologies like Bluetooth, the typical simple remote uses infrared. Another mistake is to pick visible light because of the idea of a flashing lamp. Remember that the beam from a standard TV remote is invisible, which matches the infrared part of the spectrum. Final Answer: A television remote control commonly uses infrared radiation to send signals to the television.

Question 11

Which of the following temperature scales is the SI absolute temperature scale that starts at absolute zero?

Accepted Answer

Introduction / Context: Temperature can be measured in several scales, including Celsius, Fahrenheit, Kelvin, and Rankine. In physics and engineering, absolute temperature scales that start at absolute zero are particularly important because many gas laws and thermodynamic relationships are simplest in these units. This question asks you to identify the SI absolute temperature scale that begins at absolute zero. Given Data / Assumptions: Absolute zero is the theoretical temperature at which the thermal motion of particles is minimal. Celsius and Fahrenheit are relative scales with arbitrary zero points based on water properties. Kelvin and Rankine are absolute scales starting at absolute zero, but differ in step size. The SI system adopts one of these as its official base unit for temperature. Concept / Approach: The Kelvin scale is the SI base unit of thermodynamic temperature. It starts at absolute zero, which corresponds to 0 kelvin, and uses the same size degree as the Celsius scale. Rankine is an absolute temperature scale used mainly in some engineering contexts that also starts at absolute zero but uses the Fahrenheit degree size. Celsius and Fahrenheit have zero at the freezing point of water and at a chosen scale point, respectively, so they are not absolute. Since the question explicitly asks for the SI absolute scale, the Kelvin scale is the correct answer. Step-by-Step Solution: Step 1: Recall that absolute zero is defined as 0 K in the Kelvin scale. Step 2: Understand that the Kelvin scale is built so that 0 K corresponds to minus 273.15 degree Celsius approximately. Step 3: Recognise that the Celsius scale uses 0 degree at the freezing point of water and 100 degree at the boiling point at standard pressure, so it is not an absolute scale. Step 4: Note that the Fahrenheit scale uses 32 degree for the freezing point of water and 212 degree for boiling, also not absolute. Step 5: Rankine is absolute but is not the SI base unit, so when the question emphasises SI absolute scale, Kelvin is the required choice. Verification / Alternative check: Thermodynamics equations such as the ideal gas law PV = n R T require temperature in an absolute scale, usually Kelvin, in standard physics courses. Scientific literature and data tables always report fundamental thermodynamic properties in kelvin. The official SI brochure lists kelvin as one of the seven base units, confirming its status as the SI absolute temperature scale. Why Other Options Are Wrong: Rankine scale: It is an absolute scale, but based on Fahrenheit and is not the SI base unit for temperature. Celsius scale: It is a relative scale with zero at the freezing point of water and does not start at absolute zero. Fahrenheit scale: It is also a relative scale and not used as an absolute thermodynamic scale. Common Pitfalls: Students may know that both Kelvin and Rankine start at absolute zero and become unsure which one to choose. The key hint is the word SI in the question, pointing to Kelvin. Another confusion is mixing up degree symbols; Kelvin is now written simply as K without the word degree, reflecting its status as an absolute thermodynamic scale. Final Answer: The SI absolute temperature scale that starts at absolute zero is the Kelvin scale.

Question 12

In electrical energy calculations, 1 watt hour (1 Wh) is equal to how many joules of energy?

Accepted Answer

Introduction / Context: Electric energy consumption is often expressed in units such as watt hour and kilowatt hour on electricity bills. In physics, the joule is the SI unit of energy. Converting between watt hour and joules is a common task when solving numerical problems about electrical appliances, power ratings, and energy usage. This question focuses on the basic conversion for 1 watt hour. Given Data / Assumptions: Power P in watts is defined as energy per unit time, P = E / t. 1 watt equals 1 joule per second. 1 hour equals 3600 seconds. We want energy corresponding to 1 watt used for 1 hour. Concept / Approach: A watt hour is the energy consumed by a device that uses one watt of power for one hour. Since watt is joule per second, multiplying by time in seconds gives energy in joules. Therefore, 1 Wh equals 1 W multiplied by 1 hour in seconds. Knowing that 1 hour equals 3600 seconds, the calculation becomes straightforward: 1 Wh = 1 J/s times 3600 s, giving 3600 J. This relationship is the basis for scaling up to kilowatt hours, where 1 kWh equals 3.6 million joules. Step-by-Step Solution: Step 1: Start with the definition of power: P = E / t, so E = P * t. Step 2: For 1 Wh, take P = 1 watt and t = 1 hour. Step 3: Recall that 1 watt = 1 joule per second, so 1 W = 1 J/s. Step 4: Convert 1 hour to seconds: 1 hour = 60 minutes and 1 minute = 60 seconds, so 1 hour = 60 * 60 = 3600 seconds. Step 5: Calculate energy: E = (1 J/s) * 3600 s = 3600 J. Verification / Alternative check: As a cross check, consider a 100 W bulb running for 10 hours. In watt hour, energy is 100 W * 10 h = 1000 Wh, which is 1 kWh. In joules, that should be 1000 * 3600 J = 3.6 * 10^6 J. Textbook values confirm that 1 kWh equals 3.6 megajoules. Dividing by 1000 returns 3600 J per 1 Wh, confirming the conversion factor. Why Other Options Are Wrong: 360 joules: This is smaller by a factor of 10 and does not match the correct conversion. 36000 joules: This is larger by a factor of 10 and therefore incorrect. 36 joules: This is off by a factor of 100, far from the correct value. Common Pitfalls: A common mistake is to forget that there are 3600 seconds in an hour, leading to errors by factors of 60 or 600. Another confusion arises between watt hour and kilowatt hour, which differ by a factor of 1000. Remember the basic chain: 1 W = 1 J/s, 1 h = 3600 s, so 1 Wh = 3600 J, and 1 kWh = 3.6 * 10^6 J. Final Answer: One watt hour is equal to 3600 joules of energy.

Question 13

If the velocity of a moving body remains constant in both magnitude and direction with time, what is its acceleration?

Accepted Answer

Introduction / Context: Acceleration describes how quickly the velocity of an object changes with time. If velocity changes in magnitude or direction, the object is said to be accelerating. Many problems in kinematics involve recognising when acceleration is zero and when it is not. This question asks what the acceleration is if the velocity remains constant in both magnitude and direction as time passes. Given Data / Assumptions: The object has a velocity vector that does not change with time. Magnitude of velocity (speed) is constant. Direction of motion is also constant. We use the standard definition of acceleration as rate of change of velocity. Concept / Approach: Acceleration is defined as the time rate of change of velocity. If velocity is constant, then its value at any two instants is the same. The change in velocity over any time interval is zero, so the acceleration, which is change in velocity divided by time, must be zero. Non zero acceleration would imply that either the speed or the direction of motion changes. Since the question states that both are constant, acceleration must be zero. Step-by-Step Solution: Step 1: Write the definition of average acceleration: a = (v2 minus v1) / (t2 minus t1). Step 2: For constant velocity, v2 equals v1 for all time intervals, so the numerator v2 minus v1 is zero. Step 3: This gives a = 0 / (t2 minus t1) = 0, so average acceleration is zero over any time interval. Step 4: Instantaneous acceleration is the limit of average acceleration as the time interval becomes very small, which remains zero if velocity does not change. Step 5: Therefore, if velocity remains constant in both magnitude and direction, acceleration is zero. Verification / Alternative check: Consider a car moving in a straight line at 60 km per hour without speeding up, slowing down, or turning. Speedometer reading stays fixed, and there is no sideways or forward jerk felt by passengers. This real world example represents zero acceleration. In contrast, a car going around a circular track at constant speed experiences centripetal acceleration because direction changes, even though speed is constant. That situation does not match the condition given in this question, which specifies constant direction as well. Why Other Options Are Wrong: Constant but non zero: This would imply velocity is changing steadily with time, which contradicts the condition of constant velocity. Increasing with time: This suggests a growing acceleration and therefore a changing velocity, again contradicting the problem statement. Infinite: Infinite acceleration is not physically realistic in this context and would correspond to an instantaneous change in velocity, not constant motion. Common Pitfalls: Some learners think that any moving object must have some acceleration, confusing motion with change of motion. It is crucial to remember that acceleration is related to change in velocity, not just to velocity itself. If there is no change in speed or direction, there is no acceleration. Also, be careful to distinguish between constant speed with changing direction (which has centripetal acceleration) and constant velocity in a straight line, which has zero acceleration. Final Answer: If velocity is constant in both magnitude and direction, the acceleration of the body is 0.

Question 14

For an ideal synchronous motor supplied from a constant frequency source, what is the percentage speed regulation?

Accepted Answer

Introduction / Context: Speed regulation of an electric motor indicates how much the speed changes between no load and full load conditions. It is usually expressed as a percentage of full load speed. Understanding the speed characteristics of different motor types is important for selecting the right motor for applications requiring constant speed or variable speed. This question focuses on the speed regulation of an ideal synchronous motor supplied by a constant frequency AC source. Given Data / Assumptions: The motor considered is a synchronous motor. The supply frequency is constant. We assume ideal conditions without slip or significant frequency variation. Speed regulation is defined in the usual way as percentage change in speed from no load to full load. Concept / Approach: A synchronous motor runs at a speed exactly tied to the frequency of the AC supply and the number of poles in the machine. The synchronous speed Ns is given by Ns = 120 * f / P, where f is the frequency and P is the number of poles. For an ideal synchronous motor, the rotor locks in with the rotating magnetic field and runs at Ns regardless of load, as long as the motor remains in synchronism. Therefore, the speed does not drop from no load to full load, leading to zero speed regulation in the ideal case. Step-by-Step Solution: Step 1: Write the expression for synchronous speed: Ns = 120 * f / P. Step 2: Note that f and P are fixed for a given motor on a given supply, so Ns is constant. Step 3: In a synchronous motor, the rotor speed equals Ns when the motor is running in synchronism. Step 4: Define speed regulation as (N no load minus N full load) divided by N full load, all multiplied by 100 percent. Step 5: For an ideal synchronous motor, N no load equals N full load equals Ns, so the numerator is zero and speed regulation becomes zero percent. Verification / Alternative check: In contrast, induction motors exhibit slip, meaning that rotor speed is slightly less than synchronous speed and decreases further under higher load, leading to non zero speed regulation. This difference is often highlighted in textbooks to show why synchronous motors are preferred in applications that demand constant speed, such as certain synchronous condensers and power factor correction devices. This comparison supports the conclusion that synchronous motors ideally have zero speed regulation. Why Other Options Are Wrong: 1%: This might be typical for high quality induction motors but does not describe the ideal synchronous motor. 25%: This is far too high and would indicate significant speed variation with load, which is not characteristic of synchronous machines. 0.5%: This suggests a small but non zero change in speed; for an ideal synchronous motor the theoretical value is exactly zero. Common Pitfalls: Learners sometimes confuse synchronous motors with induction motors and apply the concept of slip incorrectly. Another misunderstanding is to assume some small variation in speed must always be present. While real machines have minor deviations due to practical factors, examination questions about ideal synchronous motors take speed as perfectly constant and therefore assign zero speed regulation. Final Answer: For an ideal synchronous motor on a constant frequency supply, the percentage speed regulation is zero.

Question 15

A manometer is an instrument that is commonly used in laboratories and industry to measure which physical quantity?

Accepted Answer

Introduction / Context: Many industrial and laboratory processes require accurate measurement of pressure in gases and liquids. Devices that use columns of liquid or mechanical sensors to compare pressures are called manometers. Understanding what a manometer measures is essential in fluid mechanics, chemistry, and engineering practice. This question asks you to identify the physical quantity that a manometer is designed to measure. Given Data / Assumptions: The instrument considered is a manometer. Typical manometers include U tube manometers and inclined tube manometers. The listed options include earthquake vibrations, pressure, temperature, and density of solids. We assume standard usage in fluid systems and laboratories. Concept / Approach: A manometer consists of a tube, often U shaped, partially filled with a liquid such as mercury or water. When connected to a system where pressure is to be measured, the difference in liquid column heights indicates the pressure difference between the system and a reference, often atmospheric pressure. The height difference is proportional to pressure difference, given by delta P = rho * g * h. Therefore, the primary physical quantity measured by a manometer is pressure, not temperature, density of solids, or ground motion. Step-by-Step Solution: Step 1: Recall that manometers are frequently mentioned in context with gas pressure measurement in chemistry labs and in fluid mechanics problems. Step 2: Understand that they use a liquid column whose height difference corresponds to pressure difference via the relation delta P = rho * g * h. Step 3: Note that earthquake vibrations are measured by seismometers, not by manometers. Step 4: Temperature is measured by thermometers, thermocouples, or other temperature sensors, not by manometers. Step 5: Density of solids is determined by other methods such as Archimedes principle or direct mass and volume measurements, not by manometers. Verification / Alternative check: In fluid mechanics laboratories, manometers are connected to pipelines, Venturi meters, or orifice meters to determine pressure differences across components. In chemistry, gas collection experiments use manometers to compare gas pressure with atmospheric pressure. These uses consistently involve pressure measurement. Manuals and textbooks describe manometers as pressure measuring instruments, confirming the correct association. Why Other Options Are Wrong: Earthquake vibrations: Recorded by seismographs or seismometers, not by manometers. Temperature: Measured by thermometers and similar instruments, not by liquid columns calibrated for pressure. Density of solids: Determined using mass and volume methods or dedicated density meters, not by manometers. Common Pitfalls: Students can confuse manometers with other instruments because many scientific devices end with the suffix meter. It is helpful to associate the root word mano, related to pressure, with this instrument. Remember that barometers and manometers are both pressure instruments, with barometers measuring atmospheric pressure and manometers measuring general pressure differences in fluids. Final Answer: A manometer is used to measure pressure.

Question 16

In power system protection, high voltage circuit breakers usually interrupt fault currents during which part of the short circuit current waveform?

Accepted Answer

Introduction / Context: In electrical power systems, circuit breakers are critical safety devices that interrupt fault currents such as those caused by short circuits. When a short circuit occurs, the current waveform is not immediately steady; it contains decaying components and passes through different states known as sub transient, transient, and steady state. Understanding at which stage circuit breakers typically operate is important for selecting and designing protection equipment. This question focuses on that aspect. Given Data / Assumptions: A short circuit occurs in an alternating current power system. The resulting current has an alternating component and a direct current offset component. The waveform evolves through sub transient, transient, and steady states as time passes. We are asked when circuit breakers usually interrupt the fault current. Concept / Approach: Immediately after a short circuit, the current rises to a high value that includes sub transient and transient effects due to machine reactances and the presence of a direct current component. The direct current component decays over a few cycles, and the current then approaches a steady state alternating value. Circuit breakers are designed to clear faults quickly, often within a few cycles of the power frequency, in order to limit damage and maintain system stability. Therefore, they typically interrupt the current while the waveform is still in its transient state, before the direct current component has completely decayed and before a steady state is reached. Step-by-Step Solution: Step 1: Recognise that the short circuit current at the instant of fault has a large alternating component plus a direct current offset, giving an asymmetrical waveform. Step 2: The initial very high current that decays quickly over the first few cycles is termed sub transient, and the subsequent period where the current is still higher than steady state but decaying more slowly is the transient state. Step 3: After sufficient time, the direct current offset nearly disappears and the current settles to a steady state symmetrical alternating value. Step 4: Protection relays and circuit breakers are coordinated to detect and clear faults in a small number of cycles, often well before the current reaches pure steady state but after the very first instant of sub transient behaviour. Step 5: Therefore, breakers usually operate during the transient state of short circuit current, when both alternating and residual direct current components are still present but decaying. Verification / Alternative check: Manufacturers specify breaking capacity for circuit breakers based on the expected current at the time of interruption, which includes the effect of transient and direct current offset. Time current characteristics of protection relays typically result in operating times of a few cycles for serious faults, which coincide with the transient period. This behaviour confirms that operation is associated with the transient state rather than waiting for steady state conditions. Why Other Options Are Wrong: After the direct current component has completely ceased: Waiting for the direct current component to vanish would delay fault clearing too long, increasing damage and instability. During the sub transient state only: Sub transient effects are extremely short lived, and breakers cannot usually detect and interrupt faults within this very brief window. During the steady state of the short circuit current: Clearing faults only after reaching steady state would be unsafe, as currents and mechanical forces would remain high for too long. Common Pitfalls: Students may assume that equipment should operate when conditions are steady because steady state is easier to analyse. In reality, protection devices must act quickly, and their operation often occurs when transients are still significant. It is important to distinguish between analytical convenience and actual operation times required for safety and reliability. Final Answer: Circuit breakers usually operate and interrupt fault currents during the transient state of the short circuit current.

Question 17

In the MKS system of units (metre–kilogram–second), which of the following is the standard unit of energy?

Accepted Answer

Introduction / Context: Different unit systems have been used historically in physics, such as the CGS system and the MKS system. The modern SI system is built on the MKS base units. Knowing which unit belongs to which system is important when reading formulas, converting units, and solving numerical problems. This question asks for the standard unit of energy in the MKS system. Given Data / Assumptions: The MKS system uses metre, kilogram, and second as base units. Energy is a derived quantity related to work, force, and distance. Options include joule, ohm, erg, and volt. Ohm and volt are known electrical units, and erg is associated with the CGS system. Concept / Approach: In the MKS and SI systems, the unit of energy is the joule. One joule is defined as the work done when a force of one newton moves a body through one metre in the direction of the force. In base units, this corresponds to kg * m^2 / s^2. The erg is a much smaller unit of energy used in the CGS system, where base units are centimetre, gram, and second. Ohm is the unit of electrical resistance, and volt is the unit of electric potential difference, not energy. Step-by-Step Solution: Step 1: Recall that in the MKS system, force is measured in newtons, with 1 N = 1 kg * m / s^2. Step 2: Work or energy is defined as force times distance, so W = F * s, giving units of kg * m^2 / s^2. Step 3: The name assigned to the unit kg * m^2 / s^2 in the MKS and SI systems is joule, symbol J. Step 4: Erg is the CGS unit of energy and equals 10^-7 joule, so it is not the MKS unit. Step 5: Ohm and volt are units of electrical resistance and potential difference respectively, and do not directly represent energy. Verification / Alternative check: All modern physics textbooks and scientific references express mechanical, electrical, and thermal energy in joules when using SI units. For example, electrical energy may be written as E = V * I * t in joules when V is in volts, I in amperes, and t in seconds. Historical literature using the CGS system expresses the same quantity in ergs, but that system has largely been replaced by MKS and SI units in education and industry. Why Other Options Are Wrong: Ohm: Measures electrical resistance, defined as volt per ampere, and not an energy unit. Erg: The CGS unit of energy, not the standard unit in the MKS system. Volt: Measures electric potential difference or electromotive force, not energy itself. Common Pitfalls: Some learners see ohm or volt in energy related formulas and mistakenly think they are energy units. It helps to remember that energy usually appears with the symbol J in SI, representing joules. Another confusion is between MKS and CGS systems, where the same physical quantity has different named units; understanding the base units behind each system clarifies these differences. Final Answer: In the MKS system of units, the standard unit of energy is the joule.

Question 18

The energy that ultimately drives global wind patterns in the Earth atmosphere comes primarily from which source?

Accepted Answer

Introduction / Context: Wind is the large scale movement of air in the atmosphere, and it plays a major role in weather, climate, and renewable energy generation. Understanding what powers the wind helps explain patterns such as trade winds, monsoons, and local breezes. This question asks which source ultimately provides the energy that generates wind patterns on Earth. Given Data / Assumptions: Wind refers to horizontal movement of air masses in the atmosphere. The Sun continuously supplies energy to Earth in the form of solar radiation. Ocean currents redistribute heat in the oceans but are influenced by wind and solar heating. Anemometers are instruments, not energy sources. Concept / Approach: The primary driver of wind is uneven heating of the Earth surface by solar radiation. Different regions receive different amounts of solar energy due to latitude, time of day, seasons, and surface properties. This leads to temperature differences, which cause pressure differences in the atmosphere. Air moves from regions of high pressure to low pressure, creating wind. While ocean currents and Earth rotation influence wind patterns, the original energy that sets the system in motion comes from the Sun, not from instruments or currents alone. Step-by-Step Solution: Step 1: Recognise that when solar radiation heats the Earth surface unevenly, some areas become warmer than others. Step 2: Warmer air expands and becomes less dense, rising and creating regions of lower pressure. Step 3: Cooler, denser air from surrounding higher pressure regions flows in to replace the rising warm air, creating wind. Step 4: The continuous input of solar energy maintains this cycle of heating, expansion, and air movement at global and local scales. Step 5: Anemometers only measure wind speed, and ocean currents themselves are partly driven by wind and density differences that originate from solar heating. Verification / Alternative check: Climate and meteorology textbooks consistently state that the general circulation of the atmosphere is driven by solar heating and the resulting temperature gradients. Diagrams of the global energy balance show solar radiation as the main incoming energy source, with a portion converted into kinetic energy of winds and ocean currents. While Earth rotation and topography modify wind patterns, they do not supply the energy; that role belongs to the Sun. Why Other Options Are Wrong: Anemometers: These are instruments used to measure wind speed and direction; they do not generate wind. Ocean currents alone: Ocean currents are influenced by winds, temperature differences, and salinity, and are not the primary source of energy for atmospheric wind. None of the above: Incorrect, because solar radiation is clearly the primary energy source driving winds. Common Pitfalls: Learners sometimes focus on immediate local causes like pressure differences without tracing them back to their root cause in uneven solar heating. Others may confuse cause and effect between wind and ocean currents. To avoid this, remember that the Sun is the main external energy source for the climate system, and wind is one way that this energy is redistributed around the planet. Final Answer: The energy that generates wind ultimately comes from solar radiation from the Sun.

Question 19

In typical room air conditioners and domestic refrigeration systems, which type of compressor is most commonly used in the vapour compression cycle?

Accepted Answer

Introduction / Context: Most household refrigerators and many room air conditioners use the vapour compression refrigeration cycle to transfer heat from a cooler space to a warmer environment. A key component in this cycle is the compressor, which raises the pressure and temperature of the refrigerant. Different types of compressors are used in industry, but small domestic units favour certain designs. This question asks which compressor type is usually used in common air conditioning and refrigeration applications. Given Data / Assumptions: The context is room air conditioners and domestic refrigeration systems. These systems operate at relatively low capacities compared to large industrial chillers. Compressor types listed include centrifugal, rotary, reciprocating, and axial flow. We consider traditional and widely used designs in small capacity units. Concept / Approach: Reciprocating compressors use a piston moving back and forth inside a cylinder to compress the refrigerant gas. They are widely used in small and medium capacity refrigeration and air conditioning units because they are robust, relatively simple to manufacture, and can achieve high pressure ratios. Centrifugal and axial compressors are more common in large capacity systems and gas turbines, while rotary compressors such as scroll or rotary vane types are also used but are often classified separately or considered more specialised in some basic examination questions. The safest general answer for typical small air conditioners is reciprocating compressor. Step-by-Step Solution: Step 1: Identify reciprocating compressors as piston cylinder machines that compress gas through the reciprocating motion of the piston. Step 2: Recognise that most small domestic refrigerators and many room air conditioners traditionally use hermetically sealed reciprocating compressors. Step 3: Centrifugal compressors use a rotating impeller to impart kinetic energy to the fluid and are generally adopted for high flow rate, large capacity systems. Step 4: Axial flow compressors use a series of rotating and stationary blades and are mainly found in gas turbines, not in small vapour compression units for homes. Step 5: While rotary compressors are used in some modern air conditioners, basic general knowledge questions usually highlight reciprocating compressors as the standard type for domestic refrigeration. Verification / Alternative check: Looking at specifications of common domestic refrigerators, one finds sealed reciprocating compressors specified in many models. Textbooks on refrigeration and air conditioning list reciprocating compressors as the most common type for small tonnage systems, with rotary and scroll compressors as alternatives in special designs. Large central air conditioning plants and industrial refrigeration often employ centrifugal compressors, confirming that the compressor type strongly depends on capacity and application. Why Other Options Are Wrong: Centrifugal compressor: Generally used in large scale refrigeration or air conditioning plants, not in small domestic units. Rotary compressor: Used in some air conditioners but not universally dominant at the basic level; examination keys typically emphasise reciprocating compressors for domestic equipment. Axial flow compressor: Common in gas turbines and jet engines, not in household vapour compression refrigeration systems. Common Pitfalls: Students may be aware that newer split type air conditioners sometimes advertise rotary or scroll compressors and thus may be tempted to choose rotary. However, many text based general knowledge questions still focus on traditional designs, where reciprocating compressors are cited as the usual choice for domestic applications. It is important to align your answer with the level and context of the exam while still understanding that technology evolves. Final Answer: The compressor usually used in typical room air conditioners and domestic refrigerators is the reciprocating compressor.

Question 20

In sound waves, which physical quantity primarily determines the pitch, that is, how high or low a sound is perceived by the human ear?

Accepted Answer

Introduction / Context: This question checks your understanding of the basic characteristics of sound waves and how human hearing interprets them. In physics, a sound wave can be described by its frequency, amplitude and wavelength. In everyday life we describe sounds as high pitched or low pitched. To answer correctly, you must connect the subjective idea of pitch with the correct physical parameter of the wave. Given Data / Assumptions: We are dealing with ordinary audible sound waves in air. Pitch refers to how high or low a sound seems to the listener. Amplitude, frequency, loudness and wavelength are given as options. The ear is assumed to be normal, with a typical audible range of about 20 Hz to 20000 Hz. Concept / Approach: Pitch is the sensation that allows us to order sounds on a scale from low to high. In physics, pitch is mainly linked to the frequency of the sound wave. A wave with higher frequency produces a higher pitched sound (like a whistle), while a wave with lower frequency produces a lower pitched sound (like a drum). Amplitude is related to the intensity of the sound and is perceived as loudness, not pitch. Wavelength is inversely related to frequency, but pitch is defined more directly in terms of frequency. Therefore, frequency is the correct choice. Step-by-Step Solution: Step 1: Recall that frequency is the number of complete vibrations or cycles per second and is measured in hertz (Hz). Step 2: Understand that when the frequency increases, the sound is perceived as higher in pitch, and when frequency decreases, the sound is perceived as lower. Step 3: Recognise that amplitude measures the maximum displacement of particles from their rest positions and is linked to sound intensity and loudness. Step 4: Note that loudness is a psychological response mainly dependent on amplitude, not on frequency, although the ear sensitivity also plays some role. Step 5: Observe that wavelength and frequency are related by the formula v = f * λ for a given medium, but our ears respond directly to frequency as pitch. Step 6: Conclude that frequency is the physical quantity that primarily determines pitch. Verification / Alternative check: Think of a musical instrument such as a guitar. When you tighten a string, its frequency of vibration increases and the note becomes higher pitched. The loudness does not necessarily change unless you pluck harder, which affects amplitude. Different musical notes in a scale are distinguished mainly by their frequencies. This everyday experience supports the idea that pitch depends on frequency, not directly on amplitude or wavelength. Why Other Options Are Wrong: Amplitude is associated with sound intensity and loudness, so a larger amplitude produces a louder sound, not necessarily a higher pitched one. Loudness is a perception related mainly to amplitude; it describes how strong a sound feels, not how high or low it sounds. Wavelength is linked to frequency through the speed of sound, but pitch is defined more directly in terms of frequency; different media can change wavelength without changing pitch if frequency stays constant. Common Pitfalls: Students sometimes confuse loudness and pitch because both are subjective qualities of sound. A louder sound can feel more intense but is not necessarily higher in pitch. Another mistake is to choose wavelength because of its mathematical relation to frequency, without remembering that the ear responds to how many cycles reach it per second. Focusing on the definitions helps avoid these errors: pitch corresponds to frequency, and loudness corresponds primarily to amplitude. Final Answer: The physical quantity that primarily determines the pitch of a sound is its Frequency.

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