Question 1

Which of the following is an electrical safety device specifically designed to protect sensitive electrical equipment from sudden voltage spikes and surges in the supply?

Accepted Answer

Introduction / Context: Modern homes and offices use many electronic devices such as computers, televisions, routers, and chargers that can be damaged by sudden voltage spikes on the power line. Electrical engineering and basic physics general knowledge questions often ask about the specific devices used to guard against such overvoltage events. This question focuses on identifying the correct protective device from a set of similar sounding options. Given Data / Assumptions: - Electrical devices are connected to a power supply that may experience voltage spikes.- The goal is to protect the equipment from damage due to transient overvoltages.- Several device names are listed, but only one is a standard term used in power protection. Concept / Approach: Voltage spikes, also called surges, are short duration increases in voltage that can occur due to lightning strikes, switching of heavy loads, or faults in the power system. A surge protector is a device specifically designed to limit the voltage supplied to an electrical appliance by either blocking or shorting to ground any unwanted voltages above a safe threshold. The other names in the options are either not standard terms or refer to different kinds of protection and therefore do not correctly describe the device used against voltage spikes. Step-by-Step Solution: 1. Recognise that the key phrase in the question is voltage spikes and the need to protect devices.2. Recall that the widely used term for such equipment is surge protector, often seen as power strips with built in protection.3. Compare this with the other options, which do not correspond to common industry terminology.4. Identify surge protector as a device specifically engineered to handle voltage surges.5. Conclude that surge protector is the correct choice that matches the description in the question. Verification / Alternative check: If you look at the specifications on many power strips or extension boards sold for computer equipment, they are labelled surge protectors and list a surge energy rating in joule. This marketing and technical usage confirms that the accepted name for devices protecting against voltage spikes is surge protector. No standard product is sold as a voltage unloader or current unloader in this context, which supports the identification of the correct option. Why Other Options Are Wrong: - Voltage unloader: This term is not a standard electrical engineering term and does not correspond to a recognised protective device.- Heat protector: This might describe thermal cut outs or thermostats that respond to temperature, not directly to voltage spikes.- Current unloader: Again, this is not a commonly used term and does not specifically refer to surge protection for overvoltage events. Common Pitfalls: Students sometimes get confused by unfamiliar but impressive sounding terms and may choose them over the correct, simpler name. In exam situations, it helps to trust the terms you have seen on real equipment and in textbooks. Surge protector is a widely used and easily verified name, which should make it stand out as the correct answer for this question. Final Answer: The device designed to protect electrical devices from voltage spikes is a surge protector.

Question 2

In an ordinary electric room heater or geyser, which material is commonly used as the heating element wire because of its high resistivity and ability to withstand high temperature?

Accepted Answer

Introduction / Context: Electric heaters, toasters, geysers, and similar appliances convert electrical energy into heat using a heating element. This heating element must be made of a special material with suitable electrical and mechanical properties. Questions about which alloy is used for such heating coils are very common in basic physics and general science examinations, as they connect material properties with practical applications in daily life. Given Data / Assumptions: - The appliance in question is an electric heater or similar device.- The focus is on the material used for the heating element wire.- The material must endure high temperatures without melting quickly and should have high resistivity.- Several metallic materials are listed as options. Concept / Approach: The heating element in such appliances should have high resistivity so that it becomes significantly hot when current flows through it. It should possess a high melting point, should not oxidise or break down easily at red hot temperatures, and should be mechanically strong enough to be wound into coils. Nichrome is an alloy of nickel and chromium that satisfies these requirements very well. Tungsten is used mainly in filament lamps where a very high temperature and brightness are needed, while brass and steel are not suitable as main heating element materials because their resistivity and oxidation behaviour are not ideal for this purpose. Step-by-Step Solution: 1. Recall that the desired properties for a heating element include high resistivity, high melting point, and resistance to oxidation.2. Recognise that nichrome, an alloy of nickel and chromium, is widely used in household heaters and toasters.3. Compare with tungsten, which is mainly used as a filament in incandescent bulbs rather than as open heating coils.4. Note that brass is an alloy of copper and zinc used for fittings and decorative parts, not for heating elements.5. Note that ordinary steel also oxidises and loses strength when red hot, which makes it unsuitable for long term heating element use.6. Therefore, nichrome is the correct material for the heating element in common electric heaters. Verification / Alternative check: Manufacturers and textbooks explicitly mention nichrome wire when describing the construction of electric irons, heaters, and toasters. Laboratory heating devices often list the nichrome coil as a replaceable part. This real world usage strongly confirms that nichrome is the standard choice and is the correct answer for this question. Why Other Options Are Wrong: - Tungsten: Used mainly in electric lamp filaments where the wire is enclosed in a bulb, not in open heating coils of room heaters.- Brass: Has lower resistivity and is used more for mechanical components and decorative items rather than for heating elements.- Steel: Ordinary steel suffers from oxidation and loss of strength at high temperatures and is not a standard heating element material. Common Pitfalls: Because students associate high temperature with glowing tungsten filaments, they sometimes choose tungsten in any question involving heat. It is important to distinguish between enclosed lamp filaments and open heating elements. Remember that nichrome is the correct term to associate with coils in heaters, geysers, and toasters in basic physics questions. Final Answer: Nichrome is commonly used as the heating element material in electric heaters.

Question 3

According to basic principles of fluid dynamics, when the wind speed over a region increases, the air in that region experiences a reduction in which quantity?

Accepted Answer

Introduction / Context: Weather patterns and flight principles both rely on the relationship between fluid speed and pressure. In meteorology and elementary physics, you often encounter statements that connect higher wind speed with lower air pressure. This question checks your understanding of that relationship and the basic idea behind Bernoulli principle as it applies to moving air in the atmosphere. Given Data / Assumptions: - The situation involves air, which behaves as a fluid.- Wind speed in a particular region is increasing.- We are asked what quantity of the air decreases as the speed increases.- Standard conditions and an idealised application of Bernoulli principle are assumed. Concept / Approach: Bernoulli principle states that for an incompressible, non viscous fluid flowing in a streamline, an increase in the speed of the fluid occurs simultaneously with a decrease in static pressure. In practical terms, when air flows faster over a region, the static pressure in that region drops compared to surrounding slower moving air. This concept explains lift on an aircraft wing and wind related low pressure systems in the atmosphere. Humidity, density, and aridity can change in different weather situations, but the direct and fundamental relationship in basic physics is between speed and pressure. Step-by-Step Solution: 1. Identify the fluid quantity directly linked to flow speed in Bernoulli equation, which is pressure.2. Recall that Bernoulli relation can be written as P + (1 / 2) * rho * v^2 + rho * g * h = constant along a streamline.3. For approximately constant height, an increase in velocity v must be accompanied by a decrease in static pressure P to keep the sum constant.4. Apply this idea to air: stronger winds mean higher flow speed and therefore lower pressure at that region compared to surrounding calmer air.5. Conclude that among the options, pressure is the quantity that reduces when wind speed increases. Verification / Alternative check: Weather maps often show low pressure regions associated with strong winds and storm systems. Cyclones and depressions are examples where pressure is significantly lower in the centre and wind speeds are high due to air rushing toward this low pressure area. This observational evidence from meteorology matches the theoretical expectation from Bernoulli principle and confirms that rising wind speed is associated with reduced air pressure. Why Other Options Are Wrong: - Humidity: Humidity refers to water vapour content in the air and depends on evaporation and condensation processes, not directly on wind speed alone.- Density: Air density can vary with pressure and temperature, but the simple textbook statement emphasises pressure rather than density.- Aridity: Aridity refers to dryness of a climate and is a long term measure, not an instantaneous response to increased wind speed. Common Pitfalls: Students sometimes confuse weather related terms and may connect wind mainly with humidity or dryness. While wind can influence evaporation, the direct physics relation tested here comes from Bernoulli principle. Focusing on the core fluid dynamics idea that higher speed corresponds to lower static pressure will prevent such confusion in similar exam questions. Final Answer: Increased wind speed is accompanied by a reduction in air pressure.

Question 4

In basic kinematics, the rate of change of displacement of a body with respect to time is known by which standard term?

Accepted Answer

Introduction / Context: In the study of motion, or kinematics, several related quantities describe how the position of an object changes with time. These include displacement, velocity, speed, and acceleration. This question specifically targets the definition of velocity in terms of displacement and time. Understanding these basic definitions is crucial before tackling more complex motion problems in one or more dimensions. Given Data / Assumptions: - A body undergoes displacement as time passes.- The quantity of interest is the rate at which displacement changes with time.- We assume standard definitions used in introductory physics. Concept / Approach: Displacement is a vector quantity that describes the change in position of a body, including both magnitude and direction. Velocity is defined as the rate of change of displacement with respect to time and is therefore also a vector quantity. Mathematically, average velocity = change in displacement / time interval. Instantaneous velocity is defined through the derivative of displacement with respect to time in calculus. Speed, on the other hand, is the rate of change of distance (a scalar), and acceleration is the rate of change of velocity, not displacement. Step-by-Step Solution: 1. Recall the definition of displacement as the shortest distance from the initial to the final position of the body in a specified direction.2. Recall that velocity is defined as displacement divided by time, making it the rate of change of displacement with time.3. Recognise that speed uses distance, not displacement, and is a scalar.4. Recognise that acceleration is defined as the rate of change of velocity with time, not displacement.5. Recognise that distance is itself a measure of length travelled and is not a rate of change quantity.6. Therefore, the correct term for rate of change of displacement is velocity. Verification / Alternative check: In standard formulas, velocity v is written as v = s / t, where s is displacement and t is time. Acceleration a is written as a = change in velocity / time. These two relations together verify that velocity is the first derivative of displacement with respect to time, while acceleration is the second derivative. Textbooks consistently state this hierarchy, which confirms that velocity is the rate of change of displacement. Why Other Options Are Wrong: - Acceleration: It measures how quickly velocity changes, not how displacement changes directly.- Speed: It is based on distance per unit time, has no direction, and therefore does not fully describe change in displacement.- Distance: It is a scalar measure of ground covered and is not defined as a rate of change. Common Pitfalls: Some learners confuse speed and velocity because both have the same dimensions of length per time. The key difference is that velocity uses displacement, includes direction, and fits the vector nature of motion. Remembering that acceleration is one step higher, relating to velocity change, will also help avoid mixing up these definitions in exam questions. Final Answer: The rate of change of displacement with time is called velocity.

Question 5

An object at rest remains at rest, and an object in uniform motion continues in that state of motion unless acted upon by an external unbalanced force. This statement corresponds to which law of motion formulated by Newton?

Accepted Answer

Introduction / Context: Newton laws of motion form the foundation of classical mechanics and describe how forces affect the motion of bodies. The statement given in the question is the famous law of inertia, often encountered early in physics courses. The question tests whether you can correctly associate this verbal description with the appropriate numbered law among Newton three laws of motion. Given Data / Assumptions: - An object at rest tends to remain at rest.- An object in uniform motion in a straight line continues that motion.- Any change in this state requires an external unbalanced force.- The statement is one of Newton laws of motion. Concept / Approach: Newton first law of motion is called the law of inertia. It states that if the net external force on a body is zero, the body remains at rest or moves with constant velocity in a straight line. This law formalises the idea that motion or rest alone does not require a cause but a change in motion does. Newton second law relates net force to the rate of change of momentum, and Newton third law explains the mutual nature of forces between interacting bodies. There is no fourth law in the standard set of Newton laws. Step-by-Step Solution: 1. Recognise the law of inertia from the phrase an object at rest remains at rest and an object in motion continues in motion.2. Recall that Newton first law specifically states this principle and introduces the concept of inertial frames.3. Remember that Newton second law deals with F = m * a and rate of change of momentum.4. Recall that Newton third law uses the phrase for every action there is an equal and opposite reaction.5. Note that there is no accepted Newton fourth law in the basic set taught in physics.6. Therefore, match the given statement with Newton first law of motion. Verification / Alternative check: Any introductory physics textbook labels the law of inertia as Newton first law and quotes a version very similar to the statement in the question. Classroom demonstrations, such as the tablecloth trick or inertia of a coin on a card, are always linked with the first law. These consistent associations across many learning resources confirm that the correct answer is Newton first law of motion. Why Other Options Are Wrong: - Second law of motion: This law relates net force to acceleration and does not state that bodies remain in uniform motion when net force is zero.- Third law of motion: This law describes action and reaction forces, not the persistence of motion or rest.- Fourth law of motion: There is no recognised fourth law in Newton standard formulation. Common Pitfalls: Students sometimes confuse the numbering of Newton laws, especially between the first and second. A helpful memory aid is that the first law deals with inertia and describes what happens when net force is zero, while the second law quantifies what happens when net force is non zero. Keeping this distinction clear will help you answer similar questions quickly in examinations. Final Answer: The statement describes Newton first law of motion, also known as the law of inertia.

Question 6

In classical mechanics, linear momentum of a body is defined as the product of which two physical quantities associated with the motion of the body?

Accepted Answer

Introduction / Context: Momentum is a central concept in mechanics that helps describe how difficult it is to change the motion of a moving body. It appears in Newton second law in its original form and is conserved in many collision and explosion problems. This question checks whether you know the basic definition of linear momentum in terms of simple measurable quantities like mass and velocity. Given Data / Assumptions: - We are dealing with linear momentum of a body moving in a straight line.- The definition should involve simple mechanical quantities.- Standard definitions from introductory physics are assumed. Concept / Approach: Linear momentum p of an object is defined as the product of its mass m and its velocity v. In symbolic form, p = m * v. Momentum is a vector quantity because velocity is a vector; it has both magnitude and direction. Momentum combines how much matter is moving (mass) with how fast and in what direction it is moving (velocity). This makes momentum particularly useful when analysing collisions, as total momentum of an isolated system is conserved. Inertia, force, and acceleration are related ideas but do not directly form the definition. Step-by-Step Solution: 1. Recall that momentum symbol p is defined as p = m * v.2. Identify that mass m is a scalar quantity measuring the amount of matter in the body.3. Identify that velocity v is a vector describing both the speed and direction of motion.4. Recognise that inertia is a qualitative property related to mass but not used directly in the momentum formula.5. Recognise that force and acceleration have their own relation F = m * a and do not define momentum.6. Therefore, the product of mass and velocity is the correct expression for linear momentum. Verification / Alternative check: Newton second law in its general form can be written as net force equals rate of change of momentum. If momentum were defined as some other combination, this law would not match the observed proportionality between force, mass, and acceleration. Using p = m * v gives F = m * a for constant mass, which matches experiments. This consistency across laws confirms that momentum must be the product of mass and velocity. Why Other Options Are Wrong: - Mass and inertia: Inertia is essentially the resistance to change in motion and is closely related to mass, so mass times inertia is not a standard physical quantity.- Mass and force: Their product would have units inconsistent with momentum and does not appear as a basic definition.- Mass and acceleration: The product m * a gives force, according to Newton second law, not momentum. Common Pitfalls: Because mass times acceleration appears frequently in problems, students can mistakenly associate it with momentum. Remember that momentum tells you about the current state of motion, while force tells you about the rate of change of that state. Keeping track of dimensions and units can also help: momentum has units of kilogram metre per second, while force has units of newton, which is kilogram metre per second squared. Final Answer: Linear momentum of a body is defined as the product of its mass and its velocity.

Question 7

The statement for every action there is an equal and opposite reaction corresponds to which numbered law of motion proposed by Newton?

Accepted Answer

Introduction / Context: Newton third law of motion is one of the most quoted statements in physics because it explains how forces always come in pairs. When two bodies interact, each one exerts a force on the other, and these forces are equal in magnitude and opposite in direction. The question checks whether you can correctly associate the well known slogan for every action there is an equal and opposite reaction with the correct numbered law in Newton set of three laws of motion. Given Data / Assumptions: - The statement describes a pair of forces that are equal and opposite.- The forces act on different bodies that are interacting.- We assume the standard form of Newton laws as taught in basic mechanics. Concept / Approach: Newton third law of motion states that whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first body. These forces are called action and reaction forces. They always act on different bodies but occur simultaneously. The first law deals with inertia and uniform motion, and the second law relates net force to acceleration. There is no officially recognised fourth law of motion in Newton formulation. Step-by-Step Solution: 1. Recognise the phrase for every action there is an equal and opposite reaction as the classic wording of Newton third law.2. Remember that this law concerns pairs of forces during interactions, such as a rocket pushing exhaust gases and the gases pushing back on the rocket.3. Recall that Newton first law is about inertia and net zero force, not about paired forces.4. Recall that Newton second law relates net force to acceleration and rate of change of momentum.5. Note again that there is no Newton fourth law in the standard physics curriculum.6. Conclude that the statement must correspond to Newton third law of motion. Verification / Alternative check: Examples in textbooks, such as a person walking (foot pushes ground, ground pushes foot), swimming (hand pushes water, water pushes hand), or recoil of a gun (bullet moves forward, gun moves backward), are always described as illustrations of Newton third law. The repeated use of the action reaction phrase in that context confirms that the statement in the question is exactly the verbal expression of the third law. Why Other Options Are Wrong: - First law of motion: Addresses what happens when net external force is zero and does not discuss equal and opposite force pairs explicitly.- Second law of motion: Defines the relationship between net force, mass, and acceleration and does not contain the action reaction concept.- Fourth law of motion: No such law exists in Newton classical formulation. Common Pitfalls: Students sometimes misremember which numbered law is which, especially under exam pressure. A useful memory key is to associate the phrase action and reaction with the number three, since both words have seven letters but the law is the third. Alternatively, remember the sequence: first law inertia, second law acceleration, third law interaction forces. This ordering will help you avoid mixing up the law numbers in similar questions. Final Answer: The statement corresponds to Newton third law of motion.

Question 8

According to Newton second law in momentum form, the rate of change of linear momentum of a body with respect to time is equal to which physical quantity?

Accepted Answer

Introduction / Context: Newton second law of motion can be expressed in different but equivalent forms. In its most general form, it states that the net external force on a body equals the rate of change of its linear momentum. This question aims to ensure that you can connect this momentum based definition with the simpler F = m * a version that you often use in basic problems, and identify the correct physical quantity from the options given. Given Data / Assumptions: - A body has linear momentum that may change with time.- We consider the time rate of change of this momentum.- Standard Newtonian mechanics is assumed, with constant mass unless stated otherwise. Concept / Approach: Linear momentum p is defined as p = m * v. Newton second law in its general form states that the net external force F on a body is equal to the time rate of change of its momentum, that is F = dp / dt. When mass is constant, this simplifies to F = m * dv / dt, which can be written as F = m * a, where a is acceleration. Thus, the quantity that directly equals the rate of change of momentum is net force, not area, pressure, or velocity. Step-by-Step Solution: 1. Start from the general form of Newton second law: net force F = rate of change of momentum.2. Write this mathematically as F = dp / dt, where p is linear momentum.3. Recognise that dp / dt means the derivative of momentum with respect to time, that is how quickly momentum changes.4. Compare this with the options and note that force is explicitly associated with dp / dt.5. Understand that area and pressure are unrelated geometric and thermodynamic quantities, and velocity is part of momentum but not the rate of change of momentum itself.6. Conclude that the correct answer is force. Verification / Alternative check: Consider a constant mass m moving with velocity v. Momentum p = m * v. Differentiating with respect to time gives dp / dt = m * dv / dt = m * a. From experiments, we know that the net external force is proportional to acceleration and equals m * a for constant mass. This means that F and dp / dt have the same value, confirming that force is the rate of change of momentum. Textbooks also define Newton second law explicitly using this relationship. Why Other Options Are Wrong: - Area: It measures the extent of a surface in square units and has no direct link to momentum change.- Pressure: It is defined as force per unit area and is a scalar field quantity, not the time derivative of momentum.- Velocity: It is the rate of change of displacement with time, not the rate of change of momentum. Common Pitfalls: Some students memorise only the simpler F = m * a form of the second law and forget that it originally referred to momentum. As a result, they may confuse which quantities are being differentiated. Remember that the most general and powerful statement is F equals rate of change of momentum, and everything else is a special case of this. Keeping that in mind will help you answer conceptual questions like this more confidently. Final Answer: The rate of change of linear momentum of a body is equal to the net force acting on it.

Question 9

The refractive indices of ice, kerosene, benzene, and rock salt are different. Which option correctly lists these materials from left to right in increasing order of refractive index?

Accepted Answer

Introduction / Context: Refractive index is a measure of how much the speed of light is reduced in a medium compared with its speed in vacuum. Different materials have different refractive indices, and knowing the relative values helps in understanding refraction, lens design, and optical instruments. This question asks you to identify the correct increasing order of refractive index for four common materials: ice, kerosene, benzene, and rock salt. Given Data / Assumptions: - Materials mentioned are ice, kerosene, benzene, and rock salt.- The correct order should have the smallest refractive index first and the largest last.- Approximate standard refractive indices from textbooks are assumed. Concept / Approach: Refractive index n of a material is defined as n = c / v, where c is the speed of light in vacuum and v is the speed of light in the medium. Higher refractive index means light travels more slowly and bends more when entering the material from air. Standard approximate values used in school level physics are: ice around 1.31, kerosene around 1.44, benzene around 1.50, and rock salt around 1.54. To find the increasing order, you sort these from the smallest value of n to the largest. Step-by-Step Solution: 1. Note the approximate refractive index of ice: n(ice) is about 1.31.2. Note the approximate refractive index of kerosene: n(kerosene) is about 1.44.3. Note the approximate refractive index of benzene: n(benzene) is about 1.50.4. Note the approximate refractive index of rock salt: n(rock salt) is about 1.54.5. Arrange these values from the smallest to the largest: 1.31 (ice) < 1.44 (kerosene) < 1.50 (benzene) < 1.54 (rock salt).6. Translate this ordered list into the corresponding option: ice, kerosene, benzene, rock salt. Verification / Alternative check: You can cross check this ordering by remembering some general trends. Water and ice typically have refractive indices slightly above 1.3. Many organic liquids like kerosene and benzene have higher values in the 1.4 to 1.5 range, and crystalline salts often show even higher refractive indices. This broad trend supports the detailed ordering obtained from the approximate numerical values. Textbook tables of refractive indices also list these materials in similar ranges, confirming the correct sequence. Why Other Options Are Wrong: - Rock salt, benzene, kerosene, ice: This reverses the order completely and places the highest index first and the lowest last.- Rock salt, ice, benzene, kerosene: This mixes the order and incorrectly places rock salt before ice.- Kerosene, ice, benzene, rock salt: This places kerosene before ice and disturbs the correct ascending order. Common Pitfalls: Students sometimes try to guess based only on whether a substance is solid or liquid, which can be misleading. Another error is to assume that density and refractive index always follow the same pattern, which is not strictly true. The safest approach is to memorise common refractive indices for key materials or at least remember that ice has a lower index than kerosene, kerosene is lower than benzene, and benzene is lower than rock salt. This memory aid will help you quickly identify the correct order in exams. Final Answer: The increasing order of refractive index is ice, kerosene, benzene, rock salt.

Question 10

Considering the variation of the acceleration due to gravity over the Earth surface, at which location is the weight of a given body maximum?

Accepted Answer

Introduction / Context: Weight of a body is the force with which the Earth pulls it toward the centre and is given by W = m * g, where g is the local acceleration due to gravity. The value of g is not exactly the same everywhere on the Earth surface because of rotation and the planet slightly flattened shape. This question asks where on Earth the weight of a given body is maximum, which is equivalent to asking where g has its largest value. Given Data / Assumptions: - The Earth is approximated as an oblate spheroid, slightly flattened at the poles and bulging at the equator.- Acceleration due to gravity g varies slightly with latitude.- Weight is proportional to g for a fixed mass.- Effects of local geology are neglected in favour of the general trend with latitude. Concept / Approach: There are two main reasons why g varies with latitude. First, the Earth rotation produces a centrifugal effect that reduces the effective gravity more at the equator than at the poles. Second, because of the equatorial bulge, the equator is farther from the Earth centre than the poles, and gravitational force decreases with distance from the centre. Both effects lead to a smaller value of g at the equator and a larger value at the poles. Therefore, for the same mass, weight is maximum at the poles and minimum at the equator. Step-by-Step Solution: 1. Recall that weight W is given by W = m * g.2. For fixed mass m, weight is directly proportional to acceleration due to gravity g.3. Recognise that at the poles, there is no centrifugal reduction due to rotation because the axis passes through the poles.4. Also recognise that the poles are slightly closer to the Earth centre due to its flattened shape, which increases gravitational pull.5. At the equator, centrifugal effects are maximum and the distance from the centre is slightly larger, both of which reduce the effective g.6. Therefore, g, and hence weight, has its maximum value at the poles. Verification / Alternative check: Standard numerical values given in textbooks show g around 9.78 m per s^2 at the equator and about 9.83 m per s^2 at the poles. The difference is small but measurable. Weights of precision objects are sometimes corrected for local value of g in accurate experiments. The larger polar value of g confirms that a body would weigh slightly more at the poles than at the equator. Why Other Options Are Wrong: - Equator: Here g is slightly smaller due to greater centrifugal effect and greater distance from the centre, so weight is minimum rather than maximum.- Subtropics: Values of g here are intermediate between equator and poles, not maximum.- Tropics: Similar to subtropics, these latitudes also have intermediate values of g. Common Pitfalls: Students sometimes assume weight must be the same everywhere on Earth because mass is constant. Remember that mass and weight are different; mass is intrinsic, while weight depends on the local gravitational field. Another source of confusion is thinking that being closer to the equator somehow increases gravity when the opposite is true once rotation and shape are considered. Keeping these physical reasons in mind helps answer such questions correctly. Final Answer: The weight of a body is maximum at the poles of the Earth.

Question 11

Which one of the following instruments is best suited for accurately measuring very high temperatures inside metallurgical furnaces and kilns?

Accepted Answer

Introduction / Context: Industrial processes such as metal smelting, glass making, and ceramic firing require accurate measurement of very high temperatures, often far above the boiling point of water. Ordinary clinical or laboratory thermometers cannot withstand or measure such extreme conditions. This question asks you to identify which instrument among the given options is specially designed for measuring high temperatures inside metallurgical furnaces and similar environments. Given Data / Assumptions: - The environment is a metallurgical furnace or kiln, with very high temperatures.- Contact with the hot material may be difficult or undesirable.- We need an instrument suitable for high temperature measurement, not for moderate or low temperatures. Concept / Approach: A pyrometer is an instrument specifically designed to measure high temperatures, often by detecting thermal radiation emitted by the hot body. Optical or radiation pyrometers can measure temperature from a distance without direct contact with the material. Thermocouples can also measure high temperatures, but in many textbooks and general knowledge questions, the most appropriate term connected with furnace temperature measurement is pyrometer. Mercury thermometers and common thermistors are limited to much lower temperature ranges and cannot survive or function reliably in a metallurgical furnace. Step-by-Step Solution: 1. Recognise that metallurgical furnaces can reach temperatures of more than 1000 degree Celsius.2. Note that mercury thermometers typically operate only up to about 350 degree Celsius and would fail at such temperatures.3. Understand that thermistors are semiconductor devices mainly used for moderate temperature ranges in electronics and household devices.4. Recall that thermocouples can measure high temperatures but generally require contact and are sometimes less emphasised in general knowledge questions.5. Recall that pyrometers are widely mentioned as the standard instruments for measuring high furnace temperatures, often by sensing emitted radiation.6. Therefore, identify pyrometer as the best suited instrument for measuring temperature inside metallurgical furnaces. Verification / Alternative check: Industrial practice supports this reasoning. In steel plants and glass factories, optical pyrometers are regularly used to monitor furnace and molten metal temperatures. These instruments can be pointed at the hot object without physical contact, which is practical and safe. Manuals and textbooks on industrial instrumentation specifically list pyrometers under high temperature measurement devices, confirming that this is the correct choice for the scenario described. Why Other Options Are Wrong: - Thermocouple: While capable of measuring high temperatures, it is not usually described as the specialised furnace instrument in simple general knowledge questions.- Mercury thermometer: Unsuitable at furnace temperatures because mercury and the glass bulb would not withstand such heat.- Thermistor: Typically used for lower temperature ranges in electronic circuits and home appliances, not in metallurgical furnaces. Common Pitfalls: Students sometimes choose thermocouple because they remember it is used in some high temperature applications. However, exam questions often expect the more specific term pyrometer when the context is large industrial furnaces. To avoid confusion, associate pyrometers with red hot metals and kilns, and thermocouples with more general industrial temperature sensing including but not limited to engines and pipelines. Final Answer: The most suitable device for measuring very high furnace temperatures is the pyrometer.

Question 12

When a body is said to be accelerating, what can we correctly say about the behaviour of its speed and direction of motion over time?

Accepted Answer

Introduction / Context: Acceleration is a fundamental concept in kinematics and dynamics. Many learners initially think of acceleration only as speeding up or slowing down, but in physics, acceleration is defined more generally as the rate of change of velocity. Because velocity has both magnitude and direction, acceleration can occur when either the speed changes, the direction changes, or both. This conceptual question checks whether you understand that subtlety. Given Data / Assumptions: - The body under consideration has a non zero acceleration.- Velocity is treated as a vector quantity with both magnitude (speed) and direction.- We neglect complications such as relativistic effects and focus on Newtonian mechanics. Concept / Approach: Acceleration is defined as the rate of change of velocity with respect to time. Since velocity is a vector, any change in its magnitude or its direction constitutes a change in velocity, and hence acceleration. For purely straight line motion with changing speed, both speed and velocity magnitude change. For uniform circular motion, however, the speed remains constant while direction continuously changes, and there is still acceleration toward the centre. Therefore, acceleration does not always require a change in speed, only a change in velocity, which may arise from direction change alone. Step-by-Step Solution: 1. Recall the vector definition of velocity and that acceleration measures how quickly this vector changes.2. Recognise that change in velocity can be due to change in speed, change in direction, or both.3. Consider an example of straight line motion where the body speeds up or slows down; here both speed and velocity change.4. Consider uniform circular motion, where the speed remains constant but the direction of velocity continuously changes; acceleration is present even though speed is constant.5. From these examples, conclude that when a body is accelerated, its speed may change or may remain constant, but its velocity definitely changes.6. Therefore, the correct statement among the options is that its speed may or may not change. Verification / Alternative check: Mathematically, acceleration a can be written as a = dv / dt, where v is the velocity vector. In uniform circular motion, even though the magnitude of v is constant, the vector still rotates in direction, leading to a non zero derivative. Textbook examples always highlight that a stone tied to a string and whirled in a circle is undergoing centripetal acceleration without any change in speed. This reinforces the conclusion that speed change is not mandatory for acceleration to exist. Why Other Options Are Wrong: - Its velocity never changes: By definition, acceleration implies change in velocity, so this statement contradicts the very definition.- Its speed will always change: Speed can remain constant in cases like uniform circular motion while acceleration is still present.- Its direction always changes: In straight line motion with changing speed, the direction may remain the same while magnitude changes, yet there is acceleration. Common Pitfalls: Many students equate acceleration with speeding up and ignore the role of direction. This leads to confusion in topics such as circular motion, projectiles, and motion in two dimensions. A good strategy is to always remember that velocity is a vector and acceleration measures changes in that vector. If either component, magnitude or direction, changes, acceleration is present, and this may or may not coincide with a change in speed. Final Answer: When a body is accelerated, its speed may or may not change, but its velocity always changes.

Question 13

The spring constant (stiffness) of a helical spring depends on which combination of its physical properties and dimensions?

Accepted Answer

Introduction / Context: Springs are widely used in mechanical systems to store and release energy, provide cushioning, and maintain forces. The spring constant, often represented by k, quantifies how stiff a spring is. Different springs can have very different values of k depending on how they are made. This question tests your understanding of which physical aspects of a spring influence its spring constant in a practical sense. Given Data / Assumptions: - We consider a typical helical spring, such as those used in scales or suspensions.- The options mention properties like length, thickness, diameter, and material.- We look for the most comprehensive and realistic combination that affects stiffness. Concept / Approach: The spring constant depends on both material properties and geometric factors. The material determines the elastic modulus, which is a measure of how resistant the material is to deformation. Geometric factors include the thickness (wire diameter) and the overall coil diameter and number of turns. A thicker wire usually makes the spring stiffer, while a larger coil diameter and longer spring tend to make it less stiff. Therefore, focusing only on length or only on material is not sufficient; thickness, diameter, and material all play important roles in determining the value of the spring constant. Step-by-Step Solution: 1. Recognise that a spring made from a stronger material such as steel will have a different stiffness compared with the same geometry made from a softer material.2. Observe that a spring made from a thicker wire resists stretching more than one made from a thinner wire of the same material.3. Note that the diameter of the coils influences how much the spring bends under a given load, affecting stiffness.4. Understand that while length and number of turns matter, the option that mentions thickness, diameter, and material captures key influences on the spring constant.5. Compare the given options and identify that only the option including thickness, diameter, and material reflects the combined dependence.6. Select the option stating that the spring constant depends on its thickness, its diameter, and its material. Verification / Alternative check: Practical experience supports this view. If you try compressing two springs made of the same material but with different wire thicknesses, the one with the thicker wire is clearly harder to compress. Likewise, springs made from different materials but with identical shape also display different stiffness. Engineering formulas for helical springs explicitly include material modulus, wire diameter, coil diameter, and number of turns, reinforcing the idea that several parameters jointly determine the spring constant. Why Other Options Are Wrong: - Its length only: Length influences stiffness, but it is not the only factor; material and wire thickness also matter.- Its material only: Material properties are important, yet geometry cannot be ignored.- Its length and its diameter: This combination ignores the crucial role of material type and wire thickness, making it incomplete. Common Pitfalls: Many learners focus on just one parameter when thinking about stiffness, such as material or length. Real mechanical design always considers both material properties and geometric dimensions. Remember that springs are a good example where geometry and material work together to determine behaviour, which is why the most complete option that mentions several of these factors is the correct choice. Final Answer: The spring constant depends on the spring thickness, its diameter, and the material from which it is made.

Question 14

In basic physics, which of the following physical quantities is not treated as a vector quantity and is instead regarded as a scalar?

Accepted Answer

Introduction / Context: Physical quantities in mechanics and electromagnetism are classified as scalars or vectors. Scalars have only magnitude, while vectors have both magnitude and direction and follow vector addition rules. It is important to know which commonly used quantities are vectors and which are scalars, because this affects how they are added and how equations are interpreted. This question asks you to identify which quantity among the options is not treated as a vector in standard physics. Given Data / Assumptions: - The options are acceleration, electric current, force, and velocity.- We use the conventional classification from introductory physics.- Scalar quantities do not require vector arrows in equations and do not change sign with change of direction in the same way vectors do. Concept / Approach: Acceleration is defined as the rate of change of velocity and is a vector. Force is defined through Newton second law and is a vector, since it causes changes in velocity in specific directions. Velocity itself is a vector, describing both speed and direction of motion. Electric current, however, although it has an associated direction of flow of charge, is treated as a scalar quantity in basic circuit theory. The direction information is usually encoded into the sign conventions and the orientation of circuit elements rather than treating current as a full vector in the mathematical sense. Step-by-Step Solution: 1. Recall that acceleration has magnitude and direction and obeys vector addition; for example, two accelerations in different directions combine vectorially.2. Recall that force requires both magnitude and direction, and multiple forces acting on a body are added using vector rules to find the net force.3. Recall that velocity specifies speed and direction; when adding velocities, vector addition is needed.4. Consider electric current: it is defined as the rate of flow of charge through a cross section, measured in ampere.5. In circuit analysis, current values are added algebraically using sign conventions, rather than using vector components and angles.6. Therefore, among the listed quantities, electric current is treated as a scalar in basic physics. Verification / Alternative check: In textbooks dealing with kinematics and dynamics, acceleration, force, and velocity are always written in bold or with arrows to indicate their vector nature. They are resolved into components along coordinate axes and combined using vector addition. By contrast, in basic circuit theory, currents are added using Kirchhoff current law, which sums them algebraically at a junction with sign conventions for direction. There is no need for trigonometric vector resolution, confirming that current is effectively scalar at that level of description. Why Other Options Are Wrong: - Acceleration: It is explicitly defined as a vector and can have different values depending on direction.- Force: It is a vector; the net effect of several forces depends on their directions, not just magnitudes.- Velocity: It is the vector counterpart of speed, including direction as a key part of its definition. Common Pitfalls: Students may be tempted to treat current as a vector because they speak about direction of current flow. However, in the mathematical treatment used in most introductory courses, that direction is handled by assigning positive or negative signs to scalar current values. Until you study more advanced electromagnetic field theory, it is safe and standard to classify electric current as a scalar quantity for exam purposes. Final Answer: Among the given options, electric current is not treated as a vector quantity and is regarded as a scalar.

Question 15

In heat transfer experiments using the method of mixtures, the relation heat lost equals heat gained is based on which fundamental principle?

Accepted Answer

Introduction / Context: When studying heat transfer, a common laboratory technique is the method of mixtures, where a hot body and a cold body are brought into contact inside an insulated vessel. The analysis of such experiments relies on a simple but powerful idea that the heat lost by the hotter body is equal to the heat gained by the colder body, if no heat is lost to the surroundings. This question asks you to identify the named principle on which that relation is based. Given Data / Assumptions: - Two or more bodies with different initial temperatures are mixed or placed in contact.- The system is assumed to be thermally insulated from the surroundings.- Heat flows until all bodies reach a common final temperature.- The relation heat lost equals heat gained is valid under these conditions. Concept / Approach: The method of mixtures is a central topic in calorimetry, the branch of physics that deals with measurement of heat. The fundamental idea is energy conservation: in an isolated system, total energy remains constant. In thermal processes inside an insulated calorimeter, this means that energy given up by hot objects as they cool must equal the energy absorbed by colder objects as they warm. This is expressed as heat lost by hot bodies equals heat gained by cold bodies. The named principle that encapsulates this relation in the context of measurement is called the principle of calorimetry. Step-by-Step Solution: 1. Recognise that the phrase heat lost equals heat gained is associated with mixing hot and cold substances in a calorimeter.2. Recall that calorimetry experiments aim to determine specific heat, latent heat, or final equilibrium temperature using this relation.3. Note that the underlying idea comes from conservation of energy, applied to thermal energy in an isolated system.4. Identify that this specific application and formal statement is known as the principle of calorimetry.5. Distinguish it from general thermal equilibrium, which describes equal temperatures but not explicit heat balance equations.6. Therefore, select principle of calorimetry as the correct option. Verification / Alternative check: In school laboratory manuals and physics textbooks, sections on the method of mixtures often begin with a statement such as according to the principle of calorimetry, in an isolated system, heat lost by hot bodies is equal to heat gained by cold bodies. This naming is consistent across many sources and is explicitly linked to the design of calorimeters and the analysis of mixing experiments. That repeated phrasing confirms the correctness of the answer. Why Other Options Are Wrong: - Principle of thermal equilibrium: This states that bodies in thermal contact reach the same temperature, but does not by itself give the quantitative heat balance relation.- Principle of colors: This is unrelated to heat and refers instead to optics and colour mixing.- Principle of vaporization: This concerns phase change from liquid to vapour and latent heat, not the general heat balance in mixtures. Common Pitfalls: Some learners may choose principle of thermal equilibrium because it sounds related to bodies reaching the same temperature. However, the question specifically refers to the equality of heat lost and heat gained, which is the defining statement of the principle of calorimetry. Remembering this exact phrase will help you quickly identify the correct principle in similar exam questions. Final Answer: The relation heat lost equals heat gained is based on the principle of calorimetry.

Question 16

In modern physics, the process that can be regarded as the reverse of X ray emission, in which incident X ray photons eject electrons from a material, is known as which effect?

Accepted Answer

Introduction / Context: High energy photons such as X rays can interact with matter in different ways, including emission processes and absorption processes that release electrons. When fast electrons strike a target, X rays can be emitted. The reverse process can be thought of as X ray photons striking matter and causing the emission of electrons. This question asks you to identify which named effect describes this reverse process among several important phenomena in quantum physics and spectroscopy. Given Data / Assumptions: - X ray emission involves electrons losing energy and emitting X ray photons.- The reverse would involve X ray photons transferring energy to electrons and ejecting them.- We consider well known effects studied in modern physics which involve photons and electrons. Concept / Approach: In the photoelectric effect, photons incident on a material transfer their energy to bound electrons. If the photon energy exceeds the work function of the material, electrons are ejected from the surface with some kinetic energy. This can occur with visible light, ultraviolet light, or even X rays, depending on the material and photon energy. When specifically X ray photons cause the ejection of electrons from inner shells, the process can be considered the reverse of X ray emission, where inner shell vacancies lead to emission of characteristic X rays. The Raman effect involves inelastic scattering with slight energy shifts, the Compton effect involves photon scattering with partial energy transfer, and the Zeeman effect deals with the splitting of spectral lines in a magnetic field. Step-by-Step Solution: 1. Identify that X ray emission typically occurs when high energy electrons decelerate in a target or when electrons drop from higher to lower energy levels.2. Consider the reverse process, where an incoming photon interacts with an electron and causes it to be ejected.3. Recall that the photoelectric effect describes the emission of electrons from a material when light or X rays shine on it.4. Recognise that in this process, photon energy is converted into electron kinetic energy and work function, opposite to emission where electron energy becomes photon energy.5. Compare this with Raman effect, Compton effect, and Zeeman effect, none of which is described as the reverse of X ray emission.6. Conclude that the reverse effect of X ray emission is best described by the photoelectric effect. Verification / Alternative check: In discussions of the interaction of X rays with matter, textbooks list three main processes: photoelectric absorption, Compton scattering, and pair production. Among these, photoelectric absorption involves complete removal of the photon and ejection of an electron, and is often mentioned as the reverse of characteristic X ray emission. This matches the description of the photoelectric effect, confirming that option as correct in the context of the question. Why Other Options Are Wrong: - Raman effect: Involves inelastic scattering of visible light and small shifts in photon energy; it does not primarily eject electrons from atoms.- Compton effect: Describes scattering of high energy photons with partial energy transfer to electrons, but the photon is not fully absorbed and remains present with lower energy.- Zeeman effect: Refers to the splitting of spectral lines in the presence of a magnetic field and does not involve photoemission of electrons. Common Pitfalls: Because the Compton effect also involves interaction between photons and electrons, students may confuse it with photoelectric absorption. The key difference is that in the photoelectric effect, the photon disappears and an electron is ejected, while in the Compton effect, the photon continues with reduced energy. Remembering this distinction helps you identify the photoelectric effect as the best description of the reverse of X ray emission. Final Answer: The reverse effect of X ray emission, where X ray photons eject electrons from a material, is the photoelectric effect.

Question 17

In practical optics, a convex mirror is generally chosen for which common application because it provides a wide field of view and an upright, diminished image?

Accepted Answer

Introduction / Context: Mirrors with different shapes, such as concave and convex mirrors, are used for different purposes depending on how they form images. Convex mirrors curve outward and have special image forming properties that are particularly useful in some everyday applications. This general knowledge question asks where convex mirrors are commonly used and tests whether you can connect their optical behaviour with a practical device you see daily on vehicles. Given Data / Assumptions: - The mirror under consideration is convex and curves outward.- A convex mirror produces virtual, upright, and diminished images located behind the mirror.- A wide field of view is the main advantage in the chosen application. Concept / Approach: Convex mirrors diverge light rays and make objects appear smaller than they really are, which allows them to show a larger region in a single view. This wide field of view is important for safety in driving, as the driver needs to see vehicles approaching from behind and from adjacent lanes. Therefore, convex mirrors are widely used as rear view mirrors on cars, buses, and motorcycles. Concave mirrors, on the other hand, converge light and are used in solar cookers, headlights, and some medical instruments, where focusing light is important rather than increasing field of view. Step-by-Step Solution: 1. Recall that convex mirrors always form virtual, erect, and diminished images, regardless of object position.2. Remember that these mirrors allow a larger field of view because they capture light from a wider region and form smaller images on the mirror surface.3. Identify the real world application where seeing a wide area behind and to the side is crucial, which is the rear view mirror in vehicles.4. Recognise that solar cookers require concentration of sunlight at a point, which is achieved with concave, not convex, mirrors.5. Note that headlights and some medical viewing instruments also use concave mirrors to focus or direct light strongly.6. Therefore, the application best suited for a convex mirror in the given options is the rear view mirror. Verification / Alternative check: You can verify this simply by observing the writing on many vehicle mirrors, which often say objects in the mirror are closer than they appear. This is a characteristic of convex mirrors producing reduced images. Automobile engineering diagrams and driving manuals explicitly describe using convex mirrors for side and sometimes centre rear view mirrors to provide a wide angle view. This practical confirmation supports the theoretical reasoning about convex mirrors and their common application. Why Other Options Are Wrong: - Solar cookers: They use concave mirrors to concentrate sunlight at a focal point for heating and cooking.- Ophthalmoscope: This medical instrument commonly uses a concave mirror with a small hole to focus light into the eye.- Reflector for a headlight: Headlights use concave mirrors or reflectors to direct parallel beams of light down the road. Common Pitfalls: Some students may assume that any mirror in an optical device can be convex without considering the required function. Distinguishing between applications that need focusing (concave) and those that need wide field vision (convex) will help you choose the correct mirror type. A good memory aid is to remember convex for viewing behind in vehicles and concave for concentrating light in devices like headlights and solar cookers. Final Answer: A convex mirror is generally used as a rear view mirror in vehicles.

Question 18

In the International System of Units, what is the standard SI unit used to measure frequency, that is, the number of oscillations or cycles per second?

Accepted Answer

Introduction / Context: Frequency is a fundamental concept in physics and engineering. It describes how many cycles, oscillations, or repetitions of a periodic event occur in one second. This is important in the study of sound waves, electromagnetic waves, alternating current circuits, and many other systems. The question asks you to identify the correct SI unit of frequency from a list of common units used for other physical quantities. Given Data / Assumptions: - Frequency is defined as number of cycles per second.- We are working within the International System of Units.- The options include units that belong to different domains of physics. Concept / Approach: In the SI system, the unit of frequency is the hertz, symbol Hz. One hertz corresponds to one cycle per second. Other units listed in the options relate to force, power, and capacitance: newton for force, watt for power, and farad for capacitance. Only hertz has the correct dimensional interpretation as reciprocal seconds, which aligns with the definition of frequency. Remembering this association is important for understanding wave equations and alternating current descriptions. Step-by-Step Solution: 1. Start from the definition: frequency f is equal to the number of cycles N divided by time t.2. The unit of N is dimensionless count, and the unit of time t is second, so the unit of f is 1 per second.3. In SI, one cycle per second is given a special name, hertz, abbreviated as Hz.4. Check the options: newton is unit of force, watt is unit of power, farad is unit of capacitance, and hertz is the only one that matches reciprocal seconds.5. Therefore, hertz is the correct SI unit for frequency. Verification / Alternative check: Look at common devices and descriptions: tuning radios to a certain frequency in megahertz, power systems operating at 50 Hz or 60 Hz, and audio tones described as, for example, 440 Hz for concert A. In all such real world examples, frequency is always expressed in hertz or multiples like kilohertz or megahertz. This widespread usage confirms that hertz is the correct SI unit of frequency. Why Other Options Are Wrong: - Newton: It is the SI unit of force, associated with mass times acceleration.- Watt: It is the SI unit of power, equal to one joule per second.- Farad: It is the SI unit of capacitance in electric circuits. Common Pitfalls: Because many units appear across different branches of physics, students may confuse them if they are not careful about the context. Remembering typical uses can help: newton for weight and forces, watt for electrical and mechanical power, farad for capacitors, and hertz for waves and oscillations. Keeping a mental map of which unit belongs where will make such questions easy to answer. Final Answer: The SI unit of frequency is hertz, corresponding to one cycle per second.

Question 19

In the International System of Units (SI), which unit is used to measure electric current, defined as the rate of flow of electric charge?

Accepted Answer

Introduction / Context: Electric current is one of the seven base quantities in the International System of Units. It is central to the study of electricity and electronics, describing how much electric charge passes through a cross section of a conductor per unit time. The question asks you to identify the correct SI unit used to measure this base quantity from among several units that represent other physical concepts. Given Data / Assumptions: - Electric current is defined as charge flowing per unit time.- We use SI units throughout.- The options include units for force, energy, electric current, and power. Concept / Approach: In the SI system, the base unit of electric current is the ampere, symbol A. One ampere corresponds to one coulomb of charge passing through a cross section in one second. Newton is the unit of force, joule is the unit of energy, and watt is the unit of power. None of these match the definition of current as charge per unit time, making ampere the only correct choice. Step-by-Step Solution: 1. Recall the relation I = Q / t, where I is current, Q is charge in coulomb, and t is time in second.2. From this, the unit of current is coulomb per second.3. In SI, coulomb per second is given the special name ampere, abbreviated as A.4. Examine the options: newton measures force, joule measures energy or work, watt measures power, and ampere measures current.5. Therefore, the correct SI unit of electric current is ampere. Verification / Alternative check: Everyday electrical ratings confirm this: household circuit breakers are rated in ampere, such as 6 A or 16 A, and fuses are specified similarly. Electrical instruments like ammeters are named after this unit. Also, in Ohm law, the relation V = I * R uses volt, ampere, and ohm as standard units of voltage, current, and resistance. These consistent uses verify that ampere is indeed the base unit for electric current in SI. Why Other Options Are Wrong: - Newton: Unit of force, equal to kilogram metre per second squared.- Joule: Unit of energy or work, equal to newton metre.- Watt: Unit of power, equal to joule per second. Common Pitfalls: Since all of these units appear frequently in physics, it is easy to mix them up under exam stress. A useful memory device is that ampere sounds like amp, a term widely used for current ratings in household and industrial contexts. Associating newton with forces, joule with energy, and watt with power will help keep these units clearly separated in your mind. Final Answer: The SI unit of electric current is the ampere.

Question 20

If objects seen in a vehicle rear-view mirror appear enlarged and inverted, which type of mirror is being used?

Accepted Answer

Introduction / Context: In geometrical optics, different types of mirrors form images with very specific characteristics. Plane mirrors form images of the same size, convex mirrors form diminished upright images, and concave mirrors can form magnified or diminished images that may be upright or inverted depending on the position of the object. This question asks you to connect the observed properties of the image in a rear-view mirror enlarged and inverted with the correct type of mirror. Given Data / Assumptions: The mirror is being used as a rear-view mirror in some vehicle or setup. The objects seen in the mirror appear enlarged compared with their actual size. The images are inverted (upside down) relative to the objects. We assume ideal mirrors and use standard sign conventions from school level optics. Concept / Approach: The key idea is that image properties size and orientation depend on mirror type and object position. A concave mirror can produce three main kinds of images: real inverted and magnified (object between centre of curvature C and focus F), real inverted and diminished (object beyond C), or virtual upright and magnified (object between focus F and mirror). Convex mirrors, by contrast, always give virtual, upright and diminished images. Plane mirrors always give virtual, upright images of the same size as the object. Therefore, enlarged and inverted immediately points toward a concave mirror with the object between C and F. Step-by-Step Solution: Step 1: Note that the image is enlarged, so the magnification is greater than one in magnitude. Step 2: Note that the image is inverted, meaning it is upside down relative to the object. Step 3: Recall that convex mirrors never produce inverted images; they always produce diminished upright images. Step 4: Recall that plane mirrors produce images of the same size and always upright. Step 5: Recognise that only concave mirrors can produce magnified inverted images when the object is placed between the centre of curvature and the focus. Step 6: Conclude that the mirror must be a concave mirror. Verification / Alternative check: Ray diagram construction for a concave mirror with the object between C and F shows rays converging to form a real image beyond C. The image is larger than the object and inverted. A quick comparison with ray diagrams for plane and convex mirrors confirms that those combinations never produce this enlarged inverted real image. Thus, concave mirrors are uniquely capable of matching the description given in the question. Why Other Options Are Wrong: Convex mirror: Always forms virtual, upright and diminished images, suitable for normal rear-view mirrors but not for enlarged inverted images. Cylindrical mirror: Used in special optical instruments, but the basic school level classification focuses on plane, concave and convex; cylindrical curvature alone does not specifically give the enlarged inverted rear-view effect described. Plane mirror: Always gives an image of the same size as the object and upright, so it cannot produce an enlarged inverted image. Common Pitfalls: Students sometimes memorise that rear-view mirrors in cars are convex and then mechanically choose convex even when the question explicitly describes image properties that do not match a convex mirror. The safe approach is to focus on the image characteristics given magnified and inverted and match those to the correct mirror type using ray diagrams and basic mirror formulas, rather than relying only on the word rear-view. Final Answer: A rear-view mirror that shows enlarged, inverted images must be a concave mirror.

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