UPSC CDS-1 Archives

21. Statement I : In Tundra climate, biodiversity is comparatively less. S

Statement I :
In Tundra climate, biodiversity is comparatively less.
Statement II :
Tundra climate has less reproductive warm period.

Option text is missing in the image.

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Statement I is true. Tundra climates are characterized by extremely low temperatures, short growing seasons, and often permafrost, creating harsh conditions that limit the variety and abundance of plant and animal life. Consequently, biodiversity in tundra regions is comparatively low compared to many other biomes. Statement II is also true. The short and cool summers mean the period suitable for plant growth, flowering, and reproduction, as well as for animal breeding cycles, is very brief. This ‘less reproductive warm period’ is a primary reason why fewer species can survive and reproduce effectively in the tundra, directly leading to lower biodiversity. Thus, Statement II is the correct explanation for Statement I.

Biodiversity is influenced by environmental factors like temperature, precipitation, and seasonality. Tundra environments have severe limiting factors for life.

The short growing season limits primary productivity, which in turn affects the food available for herbivores and subsequent trophic levels. Specialized adaptations are required for organisms to survive the cold and short summer in the tundra.

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22. Statement I: Portions of glacial troughs may exhibit remarkably flat f

Statement I:
Portions of glacial troughs may exhibit remarkably flat floors.
Statement II:
The flat floor in a glacial trough is produced by uniform glacial erosion.

Both the statements are individually true and Statement II is the correct explanation of Statement I

Both the statements are individually true but Statement II is not the correct explanation of Statement I

Statement I is true but Statement II is false

Statement I is false but Statement II is true

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Statement I is true; portions of glacial troughs (U-shaped valleys formed by glaciers) often have remarkably flat floors. Statement II is false. While glacial erosion (abrasion and plucking) is responsible for carving the overall U-shape and lowering the valley floor, the characteristic flatness is often achieved not solely by “uniform glacial erosion” (which is rarely truly uniform), but significantly by the deposition of glacial till (ground moraine) and outwash sediments after the ice retreats, filling irregularities on the eroded bedrock floor. Attributing the flatness purely to uniform erosion is inaccurate.

Glacial troughs are characterized by their U-shape, steep sides, and broad, often flat floor. The U-shape is formed by the powerful erosive action of the glacier flowing through a pre-glacial valley.

Processes contributing to the shape and features of a glacial trough include abrasion (grinding action of ice and embedded debris), plucking (lifting and removal of rock fragments), and basal melting. The deposition of ground moraine and later sediments like lacustrine deposits (in lakes formed after deglaciation) plays a crucial role in creating the final flat appearance of the valley floor.

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23. Statement I: Incised meanders are formed in the mature stage of a rive

Statement I:
Incised meanders are formed in the mature stage of a river.
Statement II:
Incised meanders are characterized by rejuvenation and upliftment of land.

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Both the statements are individually true and Statement II is the correct explanation of Statement I

Both the statements are individually true but Statement II is not the correct explanation of Statement I

Statement I is true but Statement II is false

Statement I is false but Statement II is true

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Statement I is false. Incised meanders are typically formed when a river that has already developed meanders on a floodplain (characteristic of the mature stage) experiences rejuvenation. Rejuvenation can be caused by processes like tectonic uplift of the land or a drop in the base level (e.g., sea level). This allows the river to cut downwards into its existing meandering channel, rather than eroding laterally across a floodplain. Statement II is true; incised meanders are specifically associated with the rejuvenation and uplift of the land, which increases the river’s erosive power.

River stages are often simplified into youthful, mature, and old. Meanders typically form in the mature stage on flatter terrain. Rejuvenation introduces a new cycle of erosion, causing vertical cutting even in a meandering course, leading to incised meanders.

Incised meanders can be either ‘entrenched’ (symmetrical valley sides, often due to rapid uplift or deep cutting) or ‘ingrown’ (asymmetrical valley sides, where some lateral erosion continues alongside vertical cutting). They are evidence of a change in the river’s energy regime after the initial meandering pattern was established.

24. Statement I: By far the most common topographic form in a Karst terrai

Statement I:
By far the most common topographic form in a Karst terrain is the sinkhole.
Statement II:
Topographically, a sinkhole is a depression that varies in depth from less than a meter to few hundred meters.

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Both the statements are individually true and Statement II is the correct explanation of Statement I

Both the statements are individually true but Statement II is not the correct explanation of Statement I

Statement I is true but Statement II is false

Statement I is false but Statement II is true

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Statement I is true as sinkholes are indeed the most common and characteristic topographic features in Karst landscapes, formed by the dissolution of soluble bedrock. Statement II is also true; sinkholes vary significantly in size and depth, from shallow depressions to large collapsed features. However, Statement II describes a characteristic of sinkholes (their varying depth) and not the reason why they are the *most common* form. The commonality arises from the widespread nature of the dissolution process in soluble rocks. Therefore, Statement II is not the correct explanation for Statement I.

Karst topography is formed by the dissolution of soluble rocks like limestone, gypsum, and dolomite. Sinkholes are depressions formed by this dissolution and are a defining feature of Karst. Sinkholes can form through solutional processes at the surface or collapse of overlying material into underlying cavities.

Other features common in Karst terrains include caves, underground drainage systems, disappearing streams, dolines, uvalas, and poljes. The size and shape of sinkholes depend on the depth of the water table, thickness of the overlying soil, and the specific rock structure.

25. Working of safety fuses depends upon magnetic effect of the current

Working of safety fuses depends upon

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magnetic effect of the current
chemical effect of the current
magnitude of the current
heating effect of the current

Select the correct answer using the code given below.

1, 2, 3 and 4

1, 2 and 3 only

3 and 4 only

4 only

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A safety fuse is designed to protect electrical circuits from overcurrents. It consists of a wire made of a material with a low melting point (like tin-lead alloy) and a specific resistance. When the current flowing through the wire exceeds a safe limit (the fuse rating), the wire heats up significantly due to the **heating effect of the current** (Joule heating, H = I²Rt). If the **magnitude of the current** is sufficiently high, the heat generated melts the fuse wire, breaking the circuit and stopping the flow of current. Therefore, the working of a safety fuse depends on the magnitude of the current and its heating effect.

– The heating effect of electric current states that heat is produced when current flows through a resistance.
– The amount of heat produced is proportional to the square of the current (I²), the resistance (R), and the time (t).
– Fuse wire melts when the heat generated by excessive current raises its temperature to its melting point.
– The specific melting current is determined by the material, length, and thickness of the fuse wire.

Magnetic effect of current is used in devices like circuit breakers which use an electromagnet to trip a switch when current exceeds a limit. Chemical effect of current is associated with electrolysis. Neither magnetic nor chemical effects are the primary working principles of a simple fuse wire melting due to overcurrent. Only the magnitude of current (as it determines the heat) and the heating effect are relevant.

26. Consider the following statements: There is no net moment on a body

Consider the following statements:

There is no net moment on a body which is in equilibrium.
The momentum of a body is always conserved.
The kinetic energy of an object is always conserved.

Which of the statements given above is/are correct?

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1, 2 and 3

2 and 3 only

1 and 2 only

1 only

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Let’s evaluate each statement:
1. There is no net moment on a body which is in equilibrium. This is correct. A body is in rotational equilibrium if the net torque (moment) acting on it is zero. For complete equilibrium (translational and rotational), both the net force and net moment must be zero.
2. The momentum of a body is always conserved. This is incorrect. The momentum of a body is conserved only if the net external force acting on it is zero. If a net force acts on a body, its momentum changes according to Newton’s second law (F = dp/dt).
3. The kinetic energy of an object is always conserved. This is incorrect. Kinetic energy is conserved only in specific situations, such as elastic collisions where no energy is lost as heat, sound, or deformation, and when no non-conservative forces (like friction) do work on the object, and no external forces change its speed. For example, when an object falls under gravity, its kinetic energy increases.
Only statement 1 is correct.

– Equilibrium implies zero net force (translational equilibrium) and zero net torque or moment (rotational equilibrium).
– Momentum of a system is conserved in the absence of external forces. Momentum of a single body is conserved only if the net force on it is zero.
– Kinetic energy of an object is conserved only if no net work is done on it by non-conservative forces or if the system is isolated and interactions are perfectly elastic.

Conservation laws (momentum, energy, angular momentum) are fundamental in physics, but their application requires careful definition of the system and consideration of external interactions (forces, torques). “Always conserved” statements for a single body or general process are usually incorrect unless specific conditions are met.

27. Which one of the following is the value of one nanometer?

Which one of the following is the value of one nanometer?

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10-7 cm

10-6 cm

10-4 cm

10-3 cm

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One nanometer (nm) is a unit of length equal to 10⁻⁹ meters (m). To convert meters to centimeters (cm), we use the conversion factor 1 m = 100 cm = 10² cm.
So, 1 nm = 10⁻⁹ m = 10⁻⁹ × (10² cm) = 10⁻⁹⁺² cm = 10⁻⁷ cm.

– The prefix ‘nano’ (n) represents a factor of 10⁻⁹.
– The base unit of length in SI is the meter (m).
– 1 meter = 100 centimeters = 10² cm.
– To convert from meters to centimeters, multiply by 10².

Nanometers are commonly used to measure wavelengths of visible light, distances in atomic and molecular structures, and in nanotechnology. Other related units include micrometers (µm, 10⁻⁶ m) and picometers (pm, 10⁻¹² m).

28. Sound waves cannot travel through a

Sound waves cannot travel through a

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copper wire placed in air

silver slab placed in air

glass prism placed in water

wooden hollow pipe placed in vacuum

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Sound waves are mechanical waves, meaning they require a medium to propagate. They travel through the vibrations of particles in solids, liquids, and gases. A vacuum is a space essentially devoid of matter. Therefore, sound waves cannot travel through a vacuum because there are no particles to transmit the vibrations. A wooden hollow pipe placed in vacuum includes a region (the vacuum surrounding and possibly inside the pipe) through which sound cannot travel.

– Sound propagation requires a material medium (solid, liquid, or gas).
– Sound travels at different speeds in different media (typically fastest in solids, slower in liquids, and slowest in gases).
– Vacuum has negligible matter, so it cannot support the propagation of mechanical waves like sound.

Options A, B, and C describe scenarios where sound can travel through solid materials (copper wire, silver slab, glass prism) and/or gaseous air or liquid water. In a vacuum, even if a solid object like a wooden pipe is present, sound cannot travel *through* the vacuum space itself. If sound were generated within the solid pipe, it could travel through the pipe material, but it would not propagate outward into the vacuum. The question asks where sound cannot travel *through*, and the presence of vacuum prevents propagation across that space.

29. Which one of the following is the correct relation between the Kelvin

Which one of the following is the correct relation between the Kelvin temperature (T) and the Celsius temperature (t_c)?

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These are two independent temperature scales

T = t_c

T = t_c - 273·15

T = t_c + 273·15

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The Kelvin temperature scale is an absolute scale where 0 K is absolute zero. The Celsius scale is a relative scale where 0°C is the freezing point of water. The size of one degree Celsius is equal to the size of one kelvin. The relationship between Kelvin temperature (T) and Celsius temperature (t_c) is given by the formula T = t_c + 273.15. This means that a temperature in Celsius can be converted to Kelvin by adding 273.15.

– The Kelvin scale starts at absolute zero (0 K), where particle motion theoretically stops.
– The Celsius scale is based on the phase change points of water at standard pressure (0°C for freezing, 100°C for boiling).
– The temperature 0°C corresponds to 273.15 K.
– The formula T = t_c + 273.15 correctly shifts the zero point of the Celsius scale to match the absolute zero of the Kelvin scale while maintaining the same interval size.

For most practical purposes and in many physics problems, the value 273.15 is often approximated as 273. The freezing point of water is exactly 273.15 K and the boiling point is 373.15 K. The Kelvin scale is the standard unit of thermodynamic temperature in the International System of Units (SI).

30. Why is argon gas used along with tungsten wire in an electric bulb?

Why is argon gas used along with tungsten wire in an electric bulb?

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To increase the life of the bulb

To reduce the consumption of electricity

To make the emitted light colored

To reduce the cost of the bulb

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Argon gas is used in electric bulbs along with a tungsten filament primarily to increase the life of the bulb. At the high operating temperature of the tungsten filament, tungsten atoms tend to evaporate or sublime. The presence of an inert gas like argon at a certain pressure within the bulb reduces the rate of evaporation of the tungsten filament, making it last longer.

– Tungsten filaments operate at very high temperatures (around 2500-3000°C) to produce light by incandescence.
– High temperatures cause the tungsten metal to sublime (evaporate) from the filament.
– Evaporated tungsten atoms deposit on the cooler glass bulb wall, causing blackening.
– Sublimation thins the filament over time, eventually causing it to break.
– Inert gases like argon, krypton, or xenon, when present at pressure, impede the movement of tungsten atoms away from the filament, reducing the evaporation rate and thus prolonging the filament’s life and preventing rapid blackening of the bulb.

Early incandescent bulbs were vacuum sealed. Adding inert gas was a significant improvement in bulb technology, leading to longer-lasting and brighter bulbs compared to vacuum bulbs. While the inert gas does cause a slight loss of energy through convection, this is offset by the ability to operate the filament at a slightly higher temperature for improved efficiency and light output, while still significantly increasing bulb lifespan.