Question 1

In a domestic electric circuit, two bulbs are connected in the usual way and both are supplied from the same mains voltage. If one bulb glows noticeably brighter than the other, what can you conclude about the resistance of the brighter bulb compare…

Accepted Answer

Introduction / Context: This question tests your understanding of how power, voltage and resistance are related in simple electric circuits. In domestic wiring, bulbs are usually connected in parallel so that each receives the full mains voltage. When you see two bulbs operating at the same voltage but with different brightness, the difference must be explained in terms of their power ratings and resistances. Knowing how resistance affects power at constant voltage allows you to draw the correct conclusion. Given Data / Assumptions: Two bulbs are connected in a room in a normal household circuit. Both bulbs are supplied by the same mains voltage (for example, 230 V). One bulb glows brighter, indicating that it consumes more power. We assume the bulbs are rated for the mains voltage and are operating normally. Concept / Approach: The electrical power consumed by a device connected to a constant voltage supply is given by P = V^2 / R, where P is power, V is voltage and R is resistance. If V is the same for both bulbs because they are on the same mains, then power depends inversely on resistance. That is, a lower resistance results in higher power and therefore greater brightness for a filament bulb or similar device. Thus, the bulb that glows brighter must have smaller resistance than the dimmer one, assuming the same supply voltage. Step-by-Step Solution: Step 1: Recall the power relation for a device at constant voltage: P = V^2 / R. Step 2: In a domestic parallel connection, both bulbs receive the same mains voltage V across their terminals. Step 3: Compare the two bulbs: the brighter bulb clearly emits more light, which means it consumes more electrical power. Step 4: Since V is the same for both, a higher power P must correspond to a smaller resistance R in the formula P = V^2 / R. Step 5: Therefore, the brighter bulb has a lower resistance compared to the dimmer bulb. Verification / Alternative check: Consider standard bulb ratings: a 100 watt bulb and a 40 watt bulb, both designed for 230 volt mains. Using R = V^2 / P, the resistance of the 100 watt bulb is R100 = 230^2 / 100, and the resistance of the 40 watt bulb is R40 = 230^2 / 40. Since 100 is greater than 40, the denominator for the 40 watt bulb is smaller, making R40 larger than R100. This means the brighter, higher wattage bulb has a smaller resistance, which matches the general reasoning and confirms the answer. Why Other Options Are Wrong: Saying the brighter bulb has larger resistance contradicts P = V^2 / R at constant voltage, where larger resistance would give lower power and dimmer light. Claiming both bulbs have the same resistance cannot explain the observed difference in brightness if voltage is the same. Stating that no conclusion can be drawn ignores the clear mathematical relation between power, voltage and resistance in parallel connected bulbs. Common Pitfalls: Some students mistakenly think that a larger resistance must mean a stronger or better bulb and therefore higher brightness. This confusion arises from mixing up current and voltage situations. At constant voltage, higher resistance means lower current and lower power. A good way to remember this is to focus on the formula P = V^2 / R for mains driven devices. Whenever you compare two bulbs on the same supply, the brighter one will have lower resistance. Final Answer: If two bulbs are supplied with the same mains voltage and one glows brighter, that brighter bulb has smaller resistance than the dimmer one.

Question 2

In wave physics, a standing (stationary) wave is formed under which condition?

Accepted Answer

Introduction / Context: Standing waves, also called stationary waves, are an important concept in wave physics. They appear on stretched strings, in air columns of musical instruments, and in microwave cavities. This question checks whether you know the actual physical condition required for a standing wave to form, rather than just any overlap of waves. Given Data / Assumptions: We are dealing with mechanical or electromagnetic waves traveling in a medium or along a string. A wave can be reflected from a boundary such as a fixed end or a closed pipe. The question asks under what condition a standing wave pattern appears. We assume linear superposition is valid, so overlapping waves add algebraically. Concept / Approach: A standing wave is produced when two waves of the same frequency, same amplitude, and same type travel in opposite directions and interfere continuously. In practice this usually happens when a traveling wave reflects back on itself from a boundary, and the incident and reflected waves superpose. The nodes (points of zero displacement) and antinodes (points of maximum displacement) appear at fixed positions, giving the impression that the wave is not traveling even though energy is still present in the system. Step-by-Step Solution: Step 1: Consider a string fixed at one end. A wave pulse travels along the string and is reflected from the fixed end. Step 2: If a continuous sinusoidal wave is sent, a reflected wave of the same frequency and almost the same amplitude returns in the opposite direction. Step 3: When the incident and reflected waves have the same frequency and amplitude, their superposition creates regions where the displacements always cancel (nodes) and regions where they reinforce (antinodes). Step 4: The pattern of nodes and antinodes remains fixed in space. This is called a standing or stationary wave. Step 5: Therefore, the correct condition is that a traveling wave and its reflection of the same frequency and amplitude superpose. Verification / Alternative check: Mathematically, adding two sinusoidal waves of equal amplitude A and angular frequency omega traveling in opposite directions gives a displacement y = 2*A*sin(kx)*cos(omega*t). This expression has a spatial part and a time part separated, with fixed nodes where sin(kx) = 0. This confirms that equal frequency and equal amplitude opposite traveling waves create a standing wave. Simply having a large amplitude or any overlap of different waves does not guarantee such a fixed pattern. Why Other Options Are Wrong: The amplitude of a wave becomes greater than its wavelength: Amplitude and wavelength have different dimensions; a large amplitude does not create a standing wave by itself. Two waves of different frequencies simply cross each other once: Waves of different frequencies produce a changing interference pattern, not a stable standing wave. The speed of the wave becomes zero or nearly zero: Wave speed is determined by the medium and tension; standing waves do not require the wave speed to vanish. Common Pitfalls: Students sometimes think that any interference of waves is a standing wave. In reality, the pattern is only stationary when the overlapping waves have the same frequency and amplitude and travel in opposite directions. Another confusion is to think that standing waves are motionless; in fact, the medium oscillates in place, and energy is still present even though the pattern does not travel. Final Answer: A standing wave occurs when a traveling wave and its reflected wave of the same frequency and amplitude superpose.

Question 3

In meteorology, the amount of water vapour present in the air at a given time is called what?

Accepted Answer

Introduction / Context: When we talk about weather, we often mention that the air feels dry or very sticky and moist. This feeling is related to the amount of water vapour present in the atmosphere, which is a key factor in weather prediction and human comfort. The term used to describe this quantity is extremely common in weather reports and basic science. Given Data / Assumptions: We are discussing the gaseous form of water present in the atmosphere. The focus is on how much water vapour the air contains at a given moment. We are not talking about liquid water drops like rain or visible dew on surfaces. The question asks for the correct meteorological term for this quantity. Concept / Approach: Water vapour is the invisible gaseous form of water in the atmosphere. The measure of how much water vapour is in the air is called humidity. Humidity can be expressed in various ways, such as absolute humidity or relative humidity, but at general knowledge level the single word humidity represents the amount of water vapour in the air. Dew, by contrast, is liquid water condensed on surfaces, and foam is a mixture of gas in liquid; neither describes how much vapour is in the air as a whole. Step-by-Step Solution: Step 1: Identify that the question refers to water vapour, not liquid water. Step 2: Recall that weather reports often mention phrases like high humidity or low humidity to describe how moist the air is. Step 3: Recognise that humidity specifically refers to the amount of water vapour present in the air at a given time. Step 4: Compare the options and see that hot air, dew and foam do not describe this quantity. Step 5: Conclude that humidity is the correct scientific and everyday term. Verification / Alternative check: Science textbooks define humidity as the measure of the water vapour content of the air. Devices called hygrometers measure humidity. Dew forms when air cools and water vapour condenses on surfaces, which is a result of humidity reaching saturation, but dew itself is not the name of the vapour content. The other options are clearly unrelated to this definition, confirming that humidity is the only correct answer. Why Other Options Are Wrong: Hot air: This just describes temperature, not the amount of water vapour. Dew: Dew is liquid water deposited on surfaces, not the overall vapour content of the air. Foam: Foam is a mixture of gas bubbles in a liquid, seen in soaps or waves, and has nothing to do with atmospheric water vapour. Common Pitfalls: Some learners confuse humidity with dew point, which is the temperature at which air becomes saturated and dew forms. Others think that humidity refers only to how the air feels to humans, but scientifically it always refers to water vapour content. Remember that whenever you read about moist or sticky air in weather contexts, the technical word behind it is humidity. Final Answer: The amount of water vapour in the air is called Humidity.

Question 4

If a barometric (atmospheric pressure) reading is steadily falling, this usually indicates what change in air pressure?

Accepted Answer

Introduction / Context: A barometer is used to measure atmospheric pressure, and changes in its reading help meteorologists predict upcoming weather. This question asks what it means when the barometric reading is falling. Recognising how pressure readings relate to weather systems is a basic but important part of general science and geography. Given Data / Assumptions: We have a functioning barometer measuring air pressure. The reading on the barometer is observed to be going down over time. The scale is calibrated so that higher readings indicate higher pressure and lower readings indicate lower pressure. We assume normal atmospheric conditions. Concept / Approach: Barometric pressure reflects the weight of the air above a given point. A falling barometer means that this pressure is decreasing. In weather terms, a decrease in pressure is associated with the approach of a low pressure system, which often brings clouds, wind and precipitation. The key idea is that the barometer does not show absence of pressure; it shows relative changes, and a downward trend always indicates decreasing pressure compared with earlier values. Step-by-Step Solution: Step 1: Recall that barometer readings are directly proportional to atmospheric pressure. Step 2: If the numerical reading on the barometer drops, this implies that the actual air pressure is dropping. Step 3: Match this physical change to the wording of the options. Step 4: Increasing pressure would correspond to a rising barometer, not a falling one. Step 5: Therefore, a falling barometer indicates decreasing pressure. Verification / Alternative check: Weather rules of thumb often say, "When the barometer falls, expect wet or windy weather." This is because low pressure is moving in. When the barometer rises, pressure is increasing, often bringing more settled, clear weather. The barometer never reads "no pressure"; it always reads some pressure value, even if low. Thus, relating a falling barometer to decreasing pressure is consistent with both instrument design and weather observation. Why Other Options Are Wrong: Increasing pressure: This would require the barometer reading to rise, not fall. No pressure: It is impossible to have truly zero atmospheric pressure at the Earth's surface; even in storms, some pressure remains. No significant change: A clear downward trend is by definition a change, not a constant reading. Common Pitfalls: Some students mix up the direction of change and think that a falling barometer means the instrument is "failing" rather than reading lower pressure. Others assume it must mean "bad weather" and forget that the question is specifically about pressure, not about the weather outcome. Always link falling barometer to decreasing pressure first; weather effects like rain follow from that main idea. Final Answer: A falling barometric reading usually indicates Decreasing pressure.

Question 5

Which one of the following is not considered a form of energy in basic physics?

Accepted Answer

Introduction / Context: Energy appears in many different forms in nature and technology, such as heat, sound and kinetic energy. However, some physical quantities are not themselves forms of energy but are related concepts like forces or state variables. This question checks whether you can distinguish between energy forms and other physical quantities like pressure. Given Data / Assumptions: We are working within the framework of basic school or introductory physics. Heat, sound and motion all involve energy transfer or energy associated with systems. Pressure is another important physical quantity but needs to be classified correctly. The task is to identify which option does not represent a form of energy. Concept / Approach: Energy is the capacity to do work and can appear as thermal energy (heat), kinetic energy (due to motion), potential energy, sound energy and more. Sound involves mechanical waves carrying energy through a medium. Motion corresponds to kinetic energy, which is definitely a form of energy. Pressure, in contrast, is defined as force per unit area. It describes how force is distributed over a surface; it is not itself a form of energy, although pressure differences can cause work to be done and energy to be transferred. Step-by-Step Solution: Step 1: Recognise that heat represents thermal energy, the energy associated with random motion of particles. Step 2: Recognise that sound consists of mechanical waves through which energy is transmitted from one place to another. Step 3: Recognise that motion of a body with mass corresponds to kinetic energy, given by the formula KE = (1/2)*m*v^2, clearly a form of energy. Step 4: Identify pressure as force divided by area, with units such as pascal (newton per square metre). Step 5: Observe that pressure describes a mechanical state of a system, not a direct energy form, so it is the correct answer. Verification / Alternative check: Look at standard lists of energy forms in textbooks: they usually include mechanical, thermal, chemical, electrical, nuclear, radiant (light) and sound energy. Pressure does not appear on that list; it is defined separately under properties of fluids and gases. While high pressure can store energy in compressed gases, the energy itself is potential energy of the gas, not pressure energy as a separate category. This supports the conclusion that pressure is not itself a form of energy. Why Other Options Are Wrong: Heat: This is thermal energy transfer and is accepted as a form of energy in basic science. Sound: Sound waves carry energy through a medium, often simply referred to as sound energy. Motion (kinetic energy): Motion of mass with speed is the very definition of kinetic energy, a core energy form. Common Pitfalls: Because pressure can cause work to be done (for example, pushing a piston), some students mistakenly call it a form of energy. The correct view is that pressure combined with volume change can do work and change energy, but pressure itself is a state variable like temperature or density. Keeping the definition of pressure as force per unit area in mind helps avoid this confusion. Final Answer: The quantity that is not a form of energy is Pressure.

Question 6

Which of the following power plants primarily uses a non-renewable energy source?

Accepted Answer

Introduction / Context: Energy sources can be broadly classified as renewable, which are naturally replenished, and non-renewable, which exist in limited quantities and take millions of years to form. Power plants convert these sources into usable electrical energy. This question tests your understanding of which type of plant relies mainly on a non-renewable source. Given Data / Assumptions: Wind, flowing water and ocean tides are natural phenomena that repeat regularly. Nuclear plants use fuel such as uranium, which is mined from the Earth. We classify energy sources based on whether they can be replenished on human timescales. The task is to identify the plant powered by a non-renewable resource. Concept / Approach: Renewable energy sources include wind, solar radiation, flowing water in rivers (hydro), ocean tides and geothermal heat. They are continually replenished by natural cycles and do not become permanently exhausted when used correctly. Non-renewable sources include fossil fuels and nuclear fuels such as uranium and plutonium, which are finite mineral resources. A nuclear power plant uses nuclear fission of uranium or similar fuel, so it depends on a non-renewable resource, whereas wind, hydro and tidal plants use renewable flows of energy from nature. Step-by-Step Solution: Step 1: Identify the energy source for a wind mill power plant: moving air (wind), which is driven by solar heating of the Earth and is renewable. Step 2: Identify the energy source for a hydroelectric plant: flowing or falling water in rivers and dams, which is part of the water cycle and is renewable. Step 3: Identify the energy source for a tidal power plant: ocean tides, which are caused by gravitational interactions of the Earth, Moon and Sun and are renewable. Step 4: Identify the energy source for a nuclear power plant: fission of heavy atomic nuclei such as uranium-235, a finite mineral resource in the Earth's crust. Step 5: Conclude that only the nuclear power plant relies on a non-renewable energy source. Verification / Alternative check: International energy agencies and textbooks consistently classify wind, hydro and tidal power as renewable technologies. Nuclear energy is sometimes grouped separately but is generally regarded as non-renewable because uranium deposits can be depleted and are not replenished on human timescales. Although nuclear fuel is very energy dense and long lasting, it is still mined and limited. Therefore, only the nuclear power plant fits the non-renewable category here. Why Other Options Are Wrong: Wind mill power plant: Uses wind, a renewable resource driven by the Sun and atmospheric processes. Hydroelectric power plant: Uses the water cycle, which recycles water through evaporation, condensation and rainfall and is effectively renewable. Tidal power plant: Uses tidal movements that repeatedly occur due to celestial gravity and do not get used up. Common Pitfalls: Some students confuse non-polluting with renewable. Nuclear plants emit very little carbon dioxide during operation but still use non-renewable fuel. Conversely, hydro plants are renewable but can have environmental impacts on rivers and ecosystems. Always separate the ideas of renewability (can the source be replenished?) from pollution or safety issues. Final Answer: The plant that uses a non-renewable energy source is the Nuclear power plant.

Question 7

In an ideal transformer, a step-up transformer is designed primarily to increase which electrical quantity in the secondary coil?

Accepted Answer

Introduction / Context: Transformers are widely used in electrical power systems to change voltage levels for efficient transmission and safe usage. There are two main types: step-up transformers, which raise voltage, and step-down transformers, which lower voltage. This question checks whether you know which electrical quantity a step-up transformer is intended to increase in its secondary winding. Given Data / Assumptions: We are dealing with an ideal transformer working on alternating current (AC). The transformer has primary and secondary coils wound on a common core. A step-up transformer has more turns on the secondary than on the primary. We ignore energy losses and assume constant frequency. Concept / Approach: For an ideal transformer, the ratio of secondary voltage V2 to primary voltage V1 equals the ratio of secondary turns N2 to primary turns N1. In a step-up transformer, N2 is greater than N1, so V2 is greater than V1. Power (P = V * I) is conserved approximately (neglecting losses), meaning that if voltage increases, current decreases accordingly. The frequency of AC is determined by the source and does not change in a transformer. So the key purpose of a step-up transformer is to increase voltage in the secondary coil. Step-by-Step Solution: Step 1: Use the transformer turns relation: V2 / V1 = N2 / N1. Step 2: For a step-up transformer, N2 > N1, which implies V2 > V1. Step 3: For an ideal transformer, input power equals output power, so V1 * I1 ≈ V2 * I2. Step 4: If V2 is larger than V1, then I2 must be smaller than I1 to keep power nearly constant. Step 5: The AC frequency is determined by the supply and remains the same on both sides of the transformer. Step 6: Therefore, a step-up transformer is used primarily to increase the voltage in the secondary coil. Verification / Alternative check: In power transmission, electricity generated at power stations is stepped up to very high voltages (for example, hundreds of kilovolts) before being sent through long transmission lines. This reduces current and hence resistive losses in the wires. At the receiving end, step-down transformers reduce the high voltage to safer levels for domestic and industrial use. If step-up transformers increased current or power instead of voltage, this standard design of power grids would not work as it does. Textbook diagrams of transformers always show step-up devices raising voltage, not frequency or total power. Why Other Options Are Wrong: Power delivered: In an ideal transformer, power is conserved; the transformer does not create extra power. Current in the secondary coil: For a step-up transformer, the current on the secondary side actually decreases compared to the primary. Frequency of the alternating current: Transformers do not change the frequency; the input and output frequency remain the same. Common Pitfalls: A common misunderstanding is to think that a transformer that increases voltage also increases power. This would violate energy conservation. Another mistake is to assume that more turns always mean more current, but in transformers the voltage and current trade off to keep power roughly constant. Always remember: step-up means higher voltage and lower current; step-down means lower voltage and higher current. Final Answer: A step-up transformer increases the Voltage in the secondary coil.

Question 8

In the water cycle, which process allows liquid water from the Earth's surface to enter the atmosphere as water vapour?

Accepted Answer

Introduction / Context: The water cycle describes how water moves continuously between the oceans, atmosphere and land. One important step is the conversion of liquid water at the surface into water vapour that rises into the atmosphere. This question asks you to identify the main process responsible for that change of state on a global scale. Given Data / Assumptions: We are considering the movement of water from the Earth's surface into the atmosphere. Water can change state from liquid to gas under suitable conditions. Several biological and physical processes may produce vapour. The question focuses on the primary physical process in the water cycle. Concept / Approach: Evaporation is the process by which liquid water at the surface changes into water vapour. It occurs from oceans, lakes, rivers, soil and wet surfaces when molecules at the surface gain enough energy to escape into the air. Transpiration, the release of water vapour from plant leaves, also contributes to atmospheric moisture, but at basic level the main physical mechanism described in textbooks for water entering the atmosphere is evaporation. Condensation is the opposite process, where vapour turns back into liquid, forming clouds and rain, and respiration produces relatively small quantities of water vapour compared to evaporation and transpiration combined. Step-by-Step Solution: Step 1: Recall the definition of evaporation: the change of water from liquid to vapour at the surface of a liquid, even below the boiling point. Step 2: Note that large water bodies like oceans and lakes are constantly losing water to the atmosphere by evaporation. Step 3: Understand that this vapour rises, cools and later may condense to form clouds and precipitation. Step 4: Transpiration is similar in that plants release vapour, but it operates through living tissues and is usually treated separately as a biological process. Step 5: Since the question asks what process allows water to enter the atmosphere in general, the best single answer is evaporation. Verification / Alternative check: Diagrams of the water cycle in school textbooks usually show arrows from oceans and lakes to the atmosphere labeled "evaporation" and arrows from plants labeled "transpiration." Together these are sometimes called evapotranspiration, but evaporation is the main physical phase-change from liquid to gas at surfaces. Condensation is shown from clouds to droplets, which is clearly the reverse process. Respiration contributes a relatively small fraction of atmospheric vapour and is not usually highlighted in basic water cycle diagrams, supporting evaporation as the standard answer. Why Other Options Are Wrong: Transpiration from plant leaves: This does add water vapour but is a biological sub-process; the dominant physical process from large water bodies is evaporation. Respiration in animals and plants: Produces water vapour as a by-product, but its overall contribution is smaller and it is not the primary driver in the water cycle diagrams. Condensation of water vapour: This is the change of vapour back to liquid, the opposite of what is asked. Common Pitfalls: Students sometimes confuse evaporation and condensation because both involve phase changes. A good memory aid is that evaporation starts from a liquid surface and sends water up into the air, while condensation happens in the air and brings water down as droplets or rain. Also remember that plants assist through transpiration, but evaporation from oceans and lakes is the main global contributor. Final Answer: Water mainly enters the atmosphere from the surface through Evaporation from water bodies and moist surfaces.

Question 9

In digital data measurement, which of the following is the largest unit of information?

Accepted Answer

Introduction / Context: Computer storage and data sizes are measured using standard units such as kilobytes, megabytes, gigabytes and terabytes. Understanding the order of these units is important when comparing file sizes, storage devices and internet data plans. This question asks you to identify the largest unit among the options given. Given Data / Assumptions: All units refer to quantities of digital information. 1 KB, 1 MB, 1 GB and 1 TB are given in increasing or decreasing order. We are using the common hierarchy where each step represents a much larger quantity of data. We assume the standard usage in general computing, where higher prefixes represent larger units. Concept / Approach: The typical hierarchy of data units from small to large is: bit, byte, kilobyte (KB), megabyte (MB), gigabyte (GB) and terabyte (TB). Each step up usually represents a multiplication by about 1000 (in decimal) or 1024 (in binary) in capacity. Therefore, 1 TB is much larger than 1 GB, which is larger than 1 MB, which in turn is larger than 1 KB. To answer the question, we simply identify the unit with the largest prefix among kilo, mega, giga and tera. Step-by-Step Solution: Step 1: Recall the order of prefixes: kilo (10^3), mega (10^6), giga (10^9), tera (10^12). Step 2: Match each prefix to the data unit: 1 KB, 1 MB, 1 GB, 1 TB. Step 3: Recognise that tera corresponds to the highest multiplier among the listed options. Step 4: Therefore, 1 TB represents a much larger quantity of information than 1 GB, 1 MB or 1 KB. Step 5: Conclude that 1 TB (terabyte) is the largest unit of information in the given list. Verification / Alternative check: We can also think in terms of relative sizes: roughly, 1 GB is about 1000 MB, 1 MB is about 1000 KB and 1 TB is about 1000 GB. This means 1 TB is about 1,000,000 MB or about 1,000,000,000 KB, which clearly makes it the largest unit among the options. Modern hard drives and SSDs are commonly specified in terabytes, whereas smaller files like documents and images are measured in kilobytes or megabytes, confirming that TB is much larger in scale. Why Other Options Are Wrong: 1 GB (gigabyte): Larger than MB and KB but still much smaller than 1 TB. 1 MB (megabyte): Suitable for medium sized files, but far smaller than GB and TB. 1 KB (kilobyte): The smallest unit listed here, often used for very small files like text snippets. Common Pitfalls: Students sometimes mix up the order of giga and tera or think that GB and TB are almost the same. Another confusion arises when some systems display capacities using binary multiples (1024) while marketing materials use decimal multiples (1000), but in either case TB is still larger than GB. Remember the prefix order: kilo, mega, giga, tera from smaller to larger. Final Answer: The largest unit of information listed is 1 TB (terabyte).

Question 10

In geology, which of the following must be true for metamorphism of a rock to occur?

Accepted Answer

Introduction / Context: Metamorphism is the process by which existing rocks are transformed into new types of rocks through heat, pressure and chemically active fluids without the rock completely melting. This question examines your understanding of the basic conditions that must be satisfied for metamorphic changes to occur in a rock. Given Data / Assumptions: A parent rock (protolith) undergoes changes in texture and mineral composition. The temperature and pressure conditions change compared to the original environment. The rock largely remains solid and does not melt into magma. The question asks which statements are required conditions for metamorphism. Concept / Approach: By definition, metamorphic rocks form when pre-existing rocks are subjected to elevated temperatures and pressures, usually deep in the Earth's crust, but not high enough to cause complete melting. The rock must remain essentially solid, so that new minerals and textures develop in the solid state. High pressure, often combined with high temperature, drives recrystallisation and alignment of minerals. Although some metamorphism can occur at relatively shallow depths (for example, near intruding magma), most significant metamorphism happens underground rather than at the surface. Therefore, all three conditions listed are typically satisfied for classical metamorphism, and the best answer is "All of the above". Step-by-Step Solution: Step 1: Check condition A: For metamorphism, the parent rock must not melt completely; it changes while remaining largely solid. This is true and central to the definition. Step 2: Check condition B: Metamorphism is driven by high pressures and temperatures, often described as "tons of pressure" acting over long geological times, so this statement is essentially correct. Step 3: Check condition C: Most metamorphic reactions occur below the Earth's surface, where pressure and temperature are sufficient for the minerals to rearrange; this is also true. Step 4: Since each individual statement describes a real requirement or typical condition of metamorphism, the combined option "All of the above" is correct. Verification / Alternative check: Standard geology texts define metamorphism as changes in solid rocks in response to temperature, pressure and fluids, with the proviso that the rock does not cross the melting boundary. Metamorphic rocks such as gneiss, schist and marble are known to form deep in the crust, where pressure is high due to the weight of overlying layers. The presence of foliations and banded textures confirms deformation under pressure, again supporting the conditions in the options. Surface processes like weathering and erosion are not considered metamorphic. Why Other Options Are Wrong: The parent rock must remain in solid form: True but incomplete by itself, since pressure and depth also matter. High pressure must be applied over long periods: True for most metamorphism, but temperature and solid state are also important. The process must take place below the Earth's surface: Generally true, but metamorphism also requires solid state and pressure; this alone is not sufficient. Common Pitfalls: Learners sometimes think that any high temperature change produces metamorphic rock, even if melting occurs. If a rock melts and later solidifies, the product is igneous, not metamorphic. Others may overlook the importance of pressure, assuming heat alone is enough. Remember that metamorphism is a solid-state transformation driven by heat, pressure and fluids, mostly in subsurface conditions, so all three conditions in the question work together. Final Answer: For metamorphism to occur, All of the above conditions are typically true.

Question 11

Atmospheric pressure exerted on the Earth's surface is mainly due to which of the following?

Accepted Answer

Introduction / Context: Atmospheric pressure is the force per unit area exerted on the Earth's surface by the weight of the air above it. This question asks you to identify the main cause of this pressure. Understanding this concept helps explain weather patterns, barometer readings and why pressure decreases with altitude. Given Data / Assumptions: The Earth is surrounded by an atmosphere composed of gases such as nitrogen and oxygen. The atmosphere has mass and is influenced by physical forces. We are concerned with the overall force that produces the measurable air pressure at the surface. Effects such as rotation and heating may influence distribution but not the basic existence of pressure. Concept / Approach: Atmospheric pressure exists because air has weight. Air molecules are pulled toward the Earth by gravity, just as any object with mass is attracted. This gravitational attraction compresses the air near the surface, making it denser and causing it to exert a force on everything below. Rotation, revolution and uneven heating affect wind patterns, circulation and local pressure variations, but they do not create the basic vertical weight of the air. The fundamental source of atmospheric pressure is the gravitational pull of the Earth on the air column above each area. Step-by-Step Solution: Step 1: Recognise that atmospheric pressure is defined as the weight of the air per unit area. Step 2: Weight is the result of gravitational force acting on mass, here the mass of the air molecules. Step 3: The Earth's gravity pulls air downward, compressing it more strongly near the surface. Step 4: This compressed air exerts a force on surfaces in contact with it, which we measure as atmospheric pressure. Step 5: Therefore, the direct cause of atmospheric pressure is the gravitational pull of the Earth on the atmosphere. Verification / Alternative check: If the Earth had no gravity, air molecules would not be held near the surface; they would disperse into space and no significant atmospheric pressure would exist at ground level. Barometric pressure decreases with altitude because there is less air above and therefore less weight pressing down, again showing the role of gravity. Rotation and uneven heating do change the distribution of pressure horizontally (creating high and low pressure areas), but they do not create the fundamental downward force itself. Why Other Options Are Wrong: Rotation of the Earth on its axis: This contributes to phenomena like the Coriolis effect and wind patterns but is not the basic cause of atmospheric pressure. Revolution of the Earth around the Sun: This affects seasons and climate but does not directly produce the weight of the atmosphere. Uneven heating of the Earth's surface: This creates local pressure differences and winds, but the existence of pressure itself depends on gravity acting on the air mass. Common Pitfalls: Students sometimes attribute all atmospheric effects to rotation or heating because they learn about these processes in weather units. However, the key idea is that without gravity, there would be no significant atmosphere and no pressure to measure. Always separate the cause of pressure (gravity acting on mass) from the factors that redistribute pressure (heating, rotation and topography). Final Answer: Atmospheric pressure on Earth is mainly due to the Gravitational pull of the Earth on air.

Question 12

In basic mechanics, the energy associated specifically with the motion of an object is called what?

Accepted Answer

Introduction / Context: Energy comes in different forms depending on the situation. When an object is moving, it possesses energy because of its motion, which allows it to do work on other objects if it collides or interacts with them. This question asks you to recall the standard name of this type of energy in classical mechanics. Given Data / Assumptions: We are considering a physical object that has mass and a certain speed. The object is in motion, not at rest. We are asked for the type of energy directly related to this state of motion. We distinguish between kinetic and potential energy. Concept / Approach: Kinetic energy is defined as the energy an object has because of its motion. Mathematically, it is given by KE = (1/2)*m*v^2, where m is mass and v is speed. Potential energy, on the other hand, is energy stored due to the position or configuration of an object, such as gravitational potential energy of a raised object or elastic potential energy in a stretched spring. Therefore, when a question refers specifically to the energy associated with motion, it clearly points to kinetic energy, not potential energy or a combination of both. Step-by-Step Solution: Step 1: Identify that the key phrase is "associated with motion". Step 2: Recall that kinetic energy describes the ability of a moving object to do work because of its speed. Step 3: Write the formula for kinetic energy: KE = (1/2)*m*v^2. Step 4: Recognise that potential energy is related to position in a field or configuration, not to motion itself. Step 5: Conclude that the correct term for energy of motion is kinetic energy. Verification / Alternative check: Consider a rolling ball. When it is moving, it can push another ball or perform work by colliding with something. If the ball stops, its ability to do such work disappears, showing that the relevant energy depends on motion. If the ball is lifted and held at a height without moving, it has gravitational potential energy instead. Textbooks and physics problems consistently use the term kinetic energy for energy of motion, confirming the answer. Why Other Options Are Wrong: Potential energy: This refers to stored energy due to position (for example, height) or configuration (for example, compressed spring), not to motion. Both A & B: While a moving object can have both kinetic and potential energy if it is elevated, the question asks specifically which energy is associated with motion, so only kinetic energy fits exactly. None of the above: Incorrect because kinetic energy is a standard and well known term. Common Pitfalls: Some learners loosely say that "motion is energy" and do not distinguish between forms of energy. Being precise helps in solving numerical problems and understanding conservation of energy. Remember that kinetic energy always involves the square of speed, while potential energy depends on position in a force field, such as height in gravity or compression in a spring. Final Answer: The energy associated with the motion of an object is called Kinetic energy.

Question 13

In traffic safety and driving psychology, velocitation is the tendency to do which of the following?

Accepted Answer

Introduction / Context: Velocitation is a term used in driving and road safety to describe a psychological effect related to speed perception. After driving at high speed for some time, a driver's judgement of what feels "normal" can become distorted. This question checks whether you understand in which direction that distortion usually goes. Given Data / Assumptions: A driver has been traveling at a relatively high speed for an extended period, for example on a highway. Suddenly, the driver enters a slower speed zone or decides to reduce speed. The driver relies on feeling rather than checking the speedometer. The term velocitation describes the resulting mismatch between perceived and actual speed. Concept / Approach: When a driver has been moving quickly for a long time, the body and brain adapt to the high speed. That speed begins to feel comfortable and "normal." If the driver then slows down to a safer or legal limit, it may subjectively feel too slow, even though the vehicle is still moving quite fast. As a result, the driver may unintentionally continue to drive faster than the posted limit, because actual speed is higher than what the driver believes. Velocitation, therefore, is the tendency to be traveling at a speed that is faster than perceived, not slower. Step-by-Step Solution: Step 1: Imagine driving at a very high speed on a long, straight highway for a considerable time. Step 2: After this experience, exiting onto a lower speed road, you reduce speed according to signs. Step 3: Subjectively, the lower legal speed may feel uncomfortably slow, even though it is correct. Step 4: If you rely only on your feeling, you might accelerate again, ending up driving faster than you realise. Step 5: This mismatch (actual speed greater than perceived speed) is called velocitation. Verification / Alternative check: Driving instruction manuals and defensive driving courses often warn about velocitation on long trips. They advise drivers to check the speedometer regularly, especially after transitioning from high speed roads to slower zones, because the mind tends to underestimate the current speed. The formal descriptions emphasise that drivers think they are traveling slower than they actually are, meaning the car is moving faster than perceived. This matches option A exactly. Why Other Options Are Wrong: Be traveling at a speed that is slower than you perceive: This describes the opposite situation, where you think you are going faster than reality; this is not the standard definition of velocitation. Accurately match your perceived speed to your actual speed: This would describe ideal perception, not a psychological bias. Avoid changes in speed entirely: This has nothing to do with the psychological effect of prolonged high speed. Common Pitfalls: Because the term is unfamiliar, some students guess randomly or assume it refers to any change in speed. Another mistake is to think of it as feeling faster than you are, whereas the real problem is feeling slower than you are after high speed driving. To remember, associate velocitation with "velocity feels low" even when it is still high, encouraging unintentional speeding. Final Answer: Velocitation is the tendency to be traveling at a speed that is faster than you perceive.

Question 14

In electrical science, electric power (the rate of doing electrical work) is measured in which unit?

Accepted Answer

Introduction / Context: Electric power describes how quickly electrical energy is converted into other forms such as light, heat or mechanical work. It is a key quantity for rating devices like bulbs, motors and appliances. This question asks for the standard unit used to measure electric power in the International System of Units (SI). Given Data / Assumptions: Power is defined as the rate at which work is done or energy is transferred. Electric power in a circuit can be calculated as P = V * I, where V is voltage and I is current. We are using SI units for all quantities. Volt, joule and ampere are standard SI units for other electrical or energy related quantities. Concept / Approach: The SI unit of power is the watt, named after James Watt. One watt equals one joule of energy per second. In electrical circuits, when one volt of potential difference causes a current of one ampere to flow, the power is one watt. Voltage is measured in volts, current in amperes and energy in joules, so none of these alone are power units. The correct answer must be the watt, which directly measures the rate of energy conversion. Step-by-Step Solution: Step 1: Recall the basic physics definition of power: P = Work / time, with the SI unit joule per second. Step 2: In electricity, we also use P = V * I, where V is in volts and I is in amperes. Step 3: The derived unit of power is one joule per second, which is assigned the special name watt (symbol W). Step 4: Recognise that volt is the unit of electric potential difference, joule is the unit of energy and ampere is the unit of current, not power. Step 5: Therefore, electric power is measured in watts. Verification / Alternative check: Everyday examples confirm this: light bulbs are rated, for example, at 9 W, 40 W or 100 W, and electric appliances often show ratings like 1000 W (1 kilowatt). Electricity bills are based on kilowatt hours, meaning kilowatts of power used over time. You never see volts or amperes used directly as the unit for power, although these quantities help calculate power. Textbooks and device labels consistently use watts and kilowatts for power ratings. Why Other Options Are Wrong: Volt: This is the SI unit of electric potential difference (voltage), not power. Joule: This is the SI unit of energy or work itself, not the rate at which energy is used. Ampere: This is the SI unit of electric current, the flow of charge per second, not power. Common Pitfalls: Because P = V * I, some students mistakenly think volt or ampere might be units of power. Others confuse watt with watt hour, which is a unit of energy, not power. A simple rule is: power is always in watts (or kilowatts), energy is in joules or watt hours, voltage in volts and current in amperes. Keeping these distinctions clear helps in solving many electrical problems correctly. Final Answer: Electric power is measured in Watt.

Question 15

The refractive index of glass with respect to water (n_glass / n_water) is approximately equal to which of the following ratios?

Accepted Answer

Introduction / Context: Refractive index is a measure of how much light slows down when it passes through a medium compared with vacuum or another medium. The refractive index of one medium with respect to another is the ratio of their absolute refractive indices. This question asks for the approximate value of the refractive index of glass with respect to water, which is important in understanding refraction at a glass water interface. Given Data / Assumptions: Typical refractive index of water with respect to air is about 1.33. Typical refractive index of common glass with respect to air is about 1.5. Refractive index of glass with respect to water is n_glass / n_water. We are choosing the closest approximate ratio from the given options. Concept / Approach: If n1 and n2 are the refractive indices of two media with respect to air or vacuum, the refractive index of medium 1 with respect to medium 2 is given by n12 = n1 / n2. Using typical values n_glass ≈ 1.5 and n_water ≈ 1.33, the ratio n_glass / n_water is approximately 1.5 / 1.33. We must evaluate this ratio and compare it with the fractions 4/3 (1.33), 9/8 (1.125), 2/3 (0.67) and 8/9 (0.89) in the options. Step-by-Step Solution: Step 1: Take standard approximate values: n_glass ≈ 1.5, n_water ≈ 1.33. Step 2: Compute the ratio n_glass / n_water ≈ 1.5 / 1.33. Step 3: Note that 1.5 / 1.33 is a little greater than 1.1 and less than 1.2, roughly about 1.13. Step 4: Compare this with the options: 4/3 ≈ 1.33, 9/8 = 1.125, 2/3 ≈ 0.67, 8/9 ≈ 0.89. Step 5: The value 1.125 (9/8) is closest to the approximate actual ratio near 1.13, so 9/8 is the best match. Verification / Alternative check: If we use slightly refined values such as n_glass = 1.52 and n_water = 1.33, the ratio becomes about 1.52 / 1.33 ≈ 1.144. This is still much closer to 1.125 than to 1.33 or any smaller value. Many exam questions on this topic use 3/2 for glass and 4/3 for water with respect to air. Then n_glass / n_water = (3/2) / (4/3) = (3/2) * (3/4) = 9/8 exactly. This shows that the theoretical simplified values used in problems are designed to give 9/8 as the clean ratio. Why Other Options Are Wrong: 4/3: This is a common approximate value for refractive index of glass or water with respect to air but not for glass with respect to water. 2/3 and 8/9: These are less than 1, which would imply that light travels slower in water than in glass to an unrealistic degree; we know glass is optically denser than water, so the ratio should be greater than 1. Common Pitfalls: A frequent mistake is to confuse refractive index with respect to air and refractive index of one medium relative to another. Students sometimes choose 4/3 automatically because it is a familiar value, ignoring that the question explicitly says "with respect to water." Always remember to use the ratio n_glass / n_water when converting between media and to check whether the result should be greater or less than 1 based on which medium is optically denser. Final Answer: The refractive index of glass with respect to water is approximately 9/8.

Question 16

When a running car stops suddenly, the passengers tend to lean forward mainly because of which physical principle?

Accepted Answer

Introduction / Context: This everyday observation from road travel illustrates a basic concept in Newtonian mechanics. When a moving vehicle stops abruptly, passengers feel a jolt and their bodies tend to lurch forward. This question checks whether you can connect that common experience with the correct physical law or principle. Given Data / Assumptions: A car is moving forward with some speed. Passengers inside the car are also moving forward with the same speed as the car. The car is brought to a sudden stop, for example by braking hard. Seat belts or other restraints may or may not be present; the important point is the tendency of the passengers. Concept / Approach: Newton's first law of motion states that a body continues in its state of rest or uniform motion in a straight line unless acted upon by an external unbalanced force. This property is called inertia. When the car stops suddenly, a large braking force acts on the car, but there is no equally strong force immediately stopping the upper body of a passenger. As a result, the passenger's body tends to continue moving forward due to inertia of motion, making the person lean or lurch forward. Gravity acts downward, not forward, and conservation of mass is unrelated to this effect. Step-by-Step Solution: Step 1: Before braking, both car and passengers are moving forward with uniform velocity. Step 2: The driver applies brakes; an external retarding force acts on the car through the wheels and road, quickly reducing the car's speed to zero. Step 3: At the exact moment of braking, the passenger's body does not experience an equally strong backward force at every point, especially in the upper body. Step 4: Due to inertia of motion, the passenger's body tends to continue moving forward even though the car slows down. Step 5: This causes the passenger to lean or lurch forward until restrained by a seat belt, seat, or muscular effort. Verification / Alternative check: This phenomenon is symmetric for acceleration: when a car starts suddenly from rest, passengers feel pushed backward because their bodies tend to remain at rest while the car moves forward. Both cases are classic examples used in textbooks to explain inertia and Newton's first law. There is no additional forward gravitational force at work, and the total mass of the system does not change, so the law of conservation of mass is not relevant. Why Other Options Are Wrong: Gravitational force pulling them forward: Gravity acts toward the centre of the Earth (downward), not forward along the direction of motion. Law of conservation of mass: Mass is simply conserved and does not explain changes in motion or the leaning forward effect. Both B & C: Only inertia of motion is the correct and sufficient explanation here. Common Pitfalls: Some learners loosely attribute all motions to gravity or confuse inertia with some mysterious "force." Inertia is not a separate force; it is the natural tendency of bodies to resist changes in their state of motion. Remember that Newton's first law is often called the law of inertia and that vehicle examples (braking, accelerating, turning) are standard illustrations of this principle. Final Answer: Passengers lean forward when a running car stops suddenly because of the Inertia of motion of their bodies.

Question 17

In music and acoustics, a gradual increase in the loudness (volume) of a sound passage is known as what?

Accepted Answer

Introduction / Context: Musical notation and terminology include specific words for changes in loudness, tone quality and dynamics. Understanding these terms is useful not only for musicians but also for general knowledge about sound and acoustics. This question asks for the correct term used when a piece of music becomes gradually louder over a period of time. Given Data / Assumptions: The sound starts at a lower volume and slowly becomes louder. We are not talking about a sudden jump in loudness, but a progressive increase. The terms given are taken from common musical vocabulary. We assume basic Western musical notation conventions. Concept / Approach: The Italian term "crescendo" is used in music to indicate that the volume should gradually increase. It is often abbreviated as "cresc." or shown graphically with a hairpin symbol opening outward. Timbre refers to the tone color or quality of a sound, distinguishing instruments from one another. Fortissimo is a dynamic marking that means "very loud," but it does not by itself imply a gradual increase. Therefore, when the question specifies a gradual increase in loudness, the correct term is crescendo. Step-by-Step Solution: Step 1: Focus on the phrase "gradual increase in loudness." Step 2: Recall that in musical scores, the instruction "crescendo" is used to indicate increasing volume over a section. Step 3: Recognise that timbre describes the quality of sound (for example, bright, dark, warm), not its volume. Step 4: Recognise that fortissimo is a static dynamic level meaning very loud, not necessarily a gradual change. Step 5: Conclude that the appropriate term for a gradual increase in loudness is crescendo. Verification / Alternative check: If you look at any music theory textbook or sheet music, you will see crescendos marked where the composer wants the sound to build up. The opposite effect, a gradual decrease in loudness, is called a diminuendo or decrescendo. Timbre is discussed in sections about instrument families and the physics of sound, and fortissimo appears as "ff" marking on notes that should be played very loudly from the start. These references confirm that crescendo is the only option that matches a gradual increase in loudness. Why Other Options Are Wrong: Timbre: Refers to the tone color or character of the sound (for example, flute versus violin), not to changes in loudness. Fortissimo: Indicates a very loud dynamic level, but not the process of getting louder over time. None of the above: Incorrect because crescendo clearly fits the description. Common Pitfalls: Students unfamiliar with Italian musical terms might confuse fortissimo with crescendo because both relate to volume. Remember that words ending with "-issimo" usually indicate degree (for example, pianissimo means very soft, fortissimo means very loud), while crescendo and diminuendo describe changes. A useful memory is that "crescendo" sounds like "growing," which matches the idea of sound growing louder. Final Answer: A gradual increase in loudness is known as a Crescendo.

Question 18

On the Earth, the acceleration due to gravity (gravitational force per unit mass) is maximum at which of the following locations?

Accepted Answer

Introduction / Context: The strength of gravity at the Earth's surface, usually represented by g, is not exactly the same everywhere. It varies slightly with latitude and altitude. This question asks where g, and therefore the gravitational force per unit mass, is maximum: at the poles, the equator or intermediate latitudes such as the tropics. Given Data / Assumptions: The Earth is not a perfect sphere; it is slightly flattened at the poles and bulged at the equator (an oblate spheroid). The Earth rotates on its axis, creating a centrifugal effect. We are comparing surface gravity values at poles, equator and tropical regions. We assume the same altitude above sea level for all locations. Concept / Approach: Two main factors affect surface gravity with latitude: the Earth's rotation and its shape. At the equator, the centrifugal effect due to rotation is maximum and slightly reduces the effective gravity. In addition, the equatorial bulge means the surface is farther from the Earth's centre, reducing gravitational attraction, which decreases with distance. At the poles there is no centrifugal reduction, and the distance to the centre is slightly smaller, so gravity is strongest there. Between these extremes are the tropics, where values are intermediate. Step-by-Step Solution: Step 1: Consider the Earth's shape. It is flattened at the poles and bulged at the equator, so the radius is smallest at the poles. Step 2: Gravity is stronger when you are closer to the Earth's centre, so this shape effect increases g at the poles. Step 3: Consider rotation. At the equator, rotational motion produces a centrifugal effect that effectively reduces weight slightly. Step 4: At the poles, the axis of rotation passes through the location, so there is no circular motion around the axis and essentially no centrifugal reduction. Step 5: Combining both effects, g is maximum at the poles, lower at mid latitudes and minimum at the equator. Verification / Alternative check: Precise measurements show g ≈ 9.78 m/s^2 at the equator and g ≈ 9.83 m/s^2 at the poles. These confirmed values match the theoretical reasoning: the poles have slightly higher gravity. The Tropic of Cancer and Tropic of Capricorn lie between equator and poles, so their g values are intermediate. Therefore, among the options given, the poles clearly correspond to maximum gravitational force per unit mass. Why Other Options Are Wrong: The Tropic of Cancer and the Tropic of Capricorn: These latitudes are neither closest to the centre of the Earth nor free of centrifugal reduction; their g values are between equator and poles. The equator: Here the Earth's radius is largest and centrifugal effect is strongest, making gravity slightly weaker rather than stronger. Common Pitfalls: Some learners assume gravity must be greatest at the equator because they think of the Earth as a perfect sphere or confuse centrifugal force direction. Others forget the role of shape and only think about rotation. A helpful summary is: smaller radius and no centrifugal effect at the poles lead to slightly stronger gravity than at the equator or tropics. Final Answer: Gravitational force is maximum at the Poles.

Question 19

In astrophysics, the main force that holds the material of a star together and keeps it bound as a single object is which of the following?

Accepted Answer

Introduction / Context: Stars such as the Sun are huge balls of hot gas and plasma. Despite the extreme temperatures and internal pressure that tend to blow material outward, stars remain held together for millions or billions of years. This question asks which fundamental force is mainly responsible for keeping a star bound as a coherent object. Given Data / Assumptions: A star consists of very hot plasma, primarily hydrogen and helium. There is outward pressure from high temperature and nuclear reactions. The star remains roughly spherical and does not fly apart easily. We are considering long term structural stability on astronomical timescales. Concept / Approach: The main force that holds a star together is gravity. Every part of the star is attracted to every other part by gravitational forces. This self gravity pulls the gas inward, balancing the outward pressure from thermal motion and radiation in a state called hydrostatic equilibrium. While electromagnetic forces (electrical and magnetic) are important on atomic scales and in local phenomena such as sunspots, they do not provide the dominant large scale binding of the entire star's mass. Ionic or chemical bonding forces are relevant in solids and molecules, not in hot stellar plasma. Step-by-Step Solution: Step 1: Recognise that a star has enormous mass, so gravitational attraction is very strong between its particles. Step 2: Understand that thermal pressure and radiation pressure push outward, trying to expand the star. Step 3: Self gravity pulls inward, opposing this expansion and holding the star together. Step 4: At equilibrium, gravitational forces inward balance the combined outward pressures, maintaining a stable star. Step 5: Therefore, gravitational forces are the fundamental binding mechanism at the scale of the whole star. Verification / Alternative check: Astrophysical models of stars are built by solving equations of hydrostatic equilibrium, which explicitly balance gravitational force against pressure. Observational evidence from star formation, stellar evolution and the existence of compact objects such as white dwarfs and neutron stars all show gravity as the dominant large scale force. Electrical and magnetic forces are significant for local structures, flares and charged particle motions, but they do not bind the total mass in the way gravity does. Why Other Options Are Wrong: Electrical forces: While charged particles experience electromagnetic forces, in a hot plasma positive and negative charges mostly balance, and electrical forces do not dominate the large scale structure of the star. Ionic forces: These are chemical bonding forces relevant in solids and molecules at low temperatures, not in extremely hot stellar interiors. Magnetic forces: Stars do have magnetic fields, but these fields shape local phenomena rather than being the primary binding force of all the stellar matter. Common Pitfalls: Because plasma is charged, some students overestimate the role of electromagnetic forces in holding a star together. Others may think of stars as "burning" like chemical flames and imagine chemical bonds being important. In reality, nuclear reactions provide energy, but gravity both initiates the high temperature conditions during formation and then continually confines the plasma against expansion. Final Answer: Stars are held together mainly by Gravitational forces.

Question 20

Ordinary glass is primarily made from which basic raw material?

Accepted Answer

Introduction / Context: Glass is a common material used in windows, bottles and many everyday objects. It is produced by melting a mixture of raw materials at high temperature. This question asks you to identify the primary basic raw material from which most ordinary glass is made. Given Data / Assumptions: We are talking about typical soda-lime glass used in windows and containers. The manufacturing process involves high temperature melting in a furnace. Several mineral ingredients may be added to adjust properties. The question focuses on the main structural ingredient. Concept / Approach: The main raw material for ordinary glass is silica, which is chemically silicon dioxide (SiO2). In practice, silica is obtained from sand. To make soda-lime glass, silica sand is mixed with sodium carbonate (soda) and calcium carbonate (limestone) and then melted. The soda lowers the melting point, and the lime improves chemical durability, but the structural network of the glass is formed by silica. Therefore, among the given options, "sand" correctly identifies the primary material from which glass is made. Step-by-Step Solution: Step 1: Recall that common glass is often called silica glass because of its high silicon dioxide content. Step 2: Recognise that silica is naturally found in sand, particularly quartz rich sand. Step 3: Note that the standard industrial batch for soda-lime glass includes sand (SiO2), soda (Na2CO3) and lime (CaCO3). Step 4: Understand that while soda and lime are important additives, the largest component by mass is silica from sand. Step 5: Therefore, the correct answer is that glass is primarily made from sand. Verification / Alternative check: Descriptions of glass manufacturing in chemistry and industrial technology textbooks always begin with silica sand as the chief ingredient. The chemical composition of typical soda-lime glass is around 70 percent silica, 15 percent soda and 10 percent lime, plus small amounts of other oxides. Silver iodide is used in some special applications such as cloud seeding and photographic materials, not as a bulk ingredient of glass. Calcium carbonate and lime are components of the mixture but not the sole or primary raw material by volume. Why Other Options Are Wrong: Calcium carbonate only and Lime only: These materials (limestone and lime) are added to the glass batch but cannot alone form ordinary glass; without silica, they would not produce typical transparent glass. Silver iodide crystals: This compound is not a main ingredient in window or container glass and is used for entirely different purposes. Common Pitfalls: Some students may remember that limestone is used in glass making and incorrectly choose calcium carbonate or lime as the main ingredient. Others might think of more exotic substances due to special glass types. To avoid confusion, always recall that silica from sand provides the basic network for glass, while other substances modify its melting point, durability and color. Final Answer: Ordinary glass is primarily made from Sand (silica) as the main ingredient.

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