UPSC CDS-2 Archives

31. Which of the following statements about universal indicator is/are tru

Which of the following statements about universal indicator is/are true ?

1. It is a mixture of several indicators.
2. It shows different colours at different concentrations of hydrogen ions in solution.
3. It helps to determine the strength of given acid and base in titration.

Select the correct answer using the code given below :

1 only

1 and 2 only

2 and 3 only

1, 2 and 3

This question was previously asked in

UPSC CDS-2 – 2021

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Statement 1: A universal indicator is indeed a mixture of several different indicators (such as thymol blue, methyl red, bromothymol blue, thymol blue) to provide colour changes over a wide range of pH values. This statement is true.
Statement 2: The colour of a universal indicator changes gradually with the concentration of hydrogen ions (or hydronium ions) in the solution, covering the full pH scale (typically from pH 0-14). Different colours correspond to different pH values, which reflect different hydrogen ion concentrations. This statement is true.
Statement 3: While a universal indicator shows the pH throughout a titration, providing insight into how the pH changes with the addition of titrant (related to strength), it does not typically help determine the *strength* in the sense of quantitative concentration determination or finding a precise endpoint for volumetric analysis in titration. Specific indicators with sharp colour changes near the equivalence point are used for accurate titration. Universal indicator gives an approximate pH, which *can* give a general idea of strength (e.g., a strong acid causes a lower pH than a weak acid at the same concentration), but it’s not its primary use in quantitative titration analysis. Therefore, this statement is less accurate or potentially misleading in the context of standard titration procedures for determining strength (concentration). Considering the options, and the definite truth of statements 1 and 2, option B (1 and 2 only) is the most likely correct answer if statement 3 is considered not entirely true or imprecise for typical quantitative strength determination in titration.

– Universal indicator is a blend of multiple indicators.
– It provides a spectrum of colours corresponding to different pH levels.
– It is useful for estimating the pH of a solution but less so for precise titration endpoints.

The pH scale is a measure of the acidity or basicity of a solution, defined by the concentration of hydrogen ions. Strong acids/bases dissociate/ionise almost completely, leading to high/low H+ concentrations (low/high pH). Weak acids/bases only partially dissociate/ionise. Universal indicator colours range typically from red (strongly acidic) through orange, yellow, green (neutral), blue, indigo to violet (strongly alkaline).

32. An athlete completes one round of a circular track of diameter 100 m i

An athlete completes one round of a circular track of diameter 100 m in 20 s. What will be the displacements after 1 minute and 10 s, respectively ?

0 m, 50 m

300 m, 100 m

300 m, 50 m

0 m, 100 m

This question was previously asked in

UPSC CDS-2 – 2021

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The athlete completes one round of a circular track (diameter 100 m, radius 50 m) in 20 seconds.
After 1 minute (60 seconds), the athlete has completed 60 s / 20 s/round = 3 full rounds. In circular motion, after completing a full circle or multiple full circles, the displacement is zero because the final position is the same as the starting position. So, displacement after 1 minute is 0 m.
After 1 minute and 10 seconds (70 seconds), the athlete has completed 70 s / 20 s/round = 3.5 rounds. This is 3 full rounds plus half a round. After 3 full rounds, the displacement is zero. The remaining half-round takes the athlete from the starting point to the diametrically opposite point on the track. The displacement in this case is the straight-line distance between the starting point and the diametrically opposite point, which is equal to the diameter of the circle. The diameter is given as 100 m. So, displacement after 1 minute and 10 seconds is 100 m.

– Displacement is the shortest distance between the initial and final positions.
– For motion along a closed loop (like a full circle), the displacement is zero if the motion starts and ends at the same point.
– For motion along half a circle, the displacement is equal to the diameter.

Distance covered is the total path length traced. In this case, distance after 60s would be 3 * circumference, and distance after 70s would be 3.5 * circumference. Displacement is a vector quantity and depends only on the initial and final positions.

33. What is the effect of pressure of a human body on sand ?

What is the effect of pressure of a human body on sand ?

Larger while standing than while lying

Smaller while standing than while lying

Same while standing or lying

Larger while standing during the daytime and smaller during the night time while lying

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UPSC CDS-2 – 2021

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Pressure is defined as force per unit area (Pressure = Force / Area). The force exerted by the human body on the sand is equal to its weight, which remains the same whether standing or lying down. However, the area of contact with the sand is significantly smaller when standing (area of feet) compared to when lying down (area of the entire body in contact). Since the force is constant, a smaller area results in larger pressure. Therefore, the pressure exerted on the sand is larger while standing than while lying down.

Pressure is inversely proportional to the area of contact for a constant force.

This principle explains why sharp objects exert more pressure than blunt objects under the same force, and why wide tires are used on vehicles intended for soft ground.

34. An electric circuit is consisting of a cell, an ammeter and a nichrome

An electric circuit is consisting of a cell, an ammeter and a nichrome wire of length l. If the length of the wire is reduced to half (l/2), then the ammeter reading

decreases to one-half.

gets doubled.

decreases to one-third.

remains unchanged.

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UPSC CDS-2 – 2021

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According to Ohm’s law, the current (I) through a circuit is inversely proportional to the resistance (R), assuming the voltage (V) is constant (from the cell). The resistance of a wire is directly proportional to its length (R ∝ l). If the length of the nichrome wire is reduced to half (l/2), its resistance becomes half (R/2). Therefore, the current (I = V/R) will double (I’ = V/(R/2) = 2V/R = 2I). The ammeter reading, which measures the current, will get doubled.

Resistance is directly proportional to length. Current is inversely proportional to resistance.

This assumes the temperature of the wire and other factors remain constant. Nichrome is used as a resistive wire material.

35. A ray of light travelling from a rarer medium to a denser medium

A ray of light travelling from a rarer medium to a denser medium

slows down and bends away from the normal.

slows down and bends towards the normal.

speeds up and bends away from the normal.

speeds up and bends towards the normal.

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UPSC CDS-2 – 2021

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When a ray of light travels from a rarer medium (like air) to a denser medium (like glass or water), its speed decreases. Due to the change in speed, the light ray bends towards the normal to the surface at the point of incidence.

Refraction is the bending of light as it passes from one medium to another.

Conversely, when light travels from a denser medium to a rarer medium, it speeds up and bends away from the normal. This phenomenon is governed by Snell’s Law.

36. The magnetic field lines inside a current carrying long solenoid are i

The magnetic field lines inside a current carrying long solenoid are in the form of

ellipse.

parabola.

hyperbola.

parallel straight lines.

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UPSC CDS-2 – 2021

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Inside a current-carrying long solenoid, the magnetic field is strong and uniform. The magnetic field lines are parallel to the axis of the solenoid and are close to each other, indicating a uniform field. They are essentially parallel straight lines within the solenoid.

The magnetic field inside an ideal long solenoid is uniform and axial.

Outside the solenoid, the magnetic field is weak and spreads out. The magnetic field lines form closed loops, emerging from one end (North pole) and entering the other end (South pole), similar to a bar magnet, but the field is concentrated and parallel inside.

37. Where should an object be placed in front of a convex lens to get a re

Where should an object be placed in front of a convex lens to get a real and enlarged image of the object ?

At twice the focal length

At infinity

Between the principal focus and twice the focal length

Beyond twice the focal length

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UPSC CDS-2 – 2021

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When an object is placed between the principal focus (F) and twice the focal length (2F) of a convex lens, a real, inverted, and enlarged image is formed beyond 2F on the other side of the lens.

The position and nature of the image formed by a convex lens depend on the object’s position relative to the focal point and 2F.

Placing the object at twice the focal length (2F) produces a real, inverted image of the same size at 2F. Placing the object at infinity produces a real, inverted, diminished image at the focal point (F). Placing the object beyond twice the focal length (beyond 2F) produces a real, inverted, diminished image between F and 2F.

38. Which one of the following Indian Ocean island nations has recently de

Which one of the following Indian Ocean island nations has recently declared a state of environmental emergency due to oil spill from a grounded ship?

Maldives

Mauritius

Madagascar

Sri Lanka

This question was previously asked in

UPSC CDS-2 – 2020

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In August 2020, the grounding of the Japanese bulk carrier MV Wakashio off the coast of Mauritius resulted in a large oil spill, prompting the country to declare a state of environmental emergency.

The MV Wakashio oil spill incident severely impacted the marine ecosystem around Mauritius.

Maldives, Madagascar, and Sri Lanka are other Indian Ocean island nations, but the specific environmental emergency due to the MV Wakashio oil spill occurred in Mauritius.

39. In August 2020, who among the following was administered the oath as t

In August 2020, who among the following was administered the oath as the Prime Minister of Sri Lanka for the fourth time?

Gotabaya Rajapaksa

Basil Rajapaksa

Mahinda Rajapaksa

Namal Rajapaksa

This question was previously asked in

UPSC CDS-2 – 2020

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Mahinda Rajapaksa was sworn in as the Prime Minister of Sri Lanka for the fourth time on August 9, 2020, following the victory of his party, Sri Lanka Podujana Peramuna (SLPP), in the parliamentary elections.

This refers to a significant political event in a neighboring country in 2020.

Gotabaya Rajapaksa is his brother and was the President of Sri Lanka at the time. Basil Rajapaksa and Namal Rajapaksa are also prominent political figures from the same family.

40. Recently, islands of Andaman and Nicobar were connected with mainland

Recently, islands of Andaman and Nicobar were connected with mainland by Submarine Optical Fibre Cable. Which one of the following islands was not connected initially?

Shaheed Island

Swaraj Island

Little Andaman

Port Blair

This question was previously asked in

UPSC CDS-2 – 2020

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The Submarine Optical Fibre Cable project connected Chennai to Port Blair and then branched out to several other islands in Andaman and Nicobar. While Port Blair was the primary landing point for the cable from the mainland, the question asks which *island* was *not* connected initially. Based on common lists of islands receiving branches from the Port Blair hub upon inauguration (like Swaraj Dweep, Shaheed Dweep, and Little Andaman which are among the options), Port Blair itself serves a different role as the main hub from the mainland. Although technically connected, it is distinct from the other islands that received branch connectivity from Port Blair. Given the likely intent of the question, Port Blair is the most plausible answer as being different in its mode of initial connection within the archipelago network compared to the other islands listed, which received spurs from the Port Blair hub.

The project involved a main cable from Chennai to Port Blair, with branches extending from Port Blair to other islands.

The project, inaugurated in August 2020, aimed to provide high-speed internet connectivity to the islands. The initial list of islands connected included Port Blair, Swaraj Dweep (Havelock), Shaheed Dweep (Neil), Long Island, Rangat, Little Andaman, Car Nicobar, Kamorta, Great Nicobar, and Campbell Bay, although some sources list slightly different initial sets. However, Shaheed, Swaraj, and Little Andaman are consistently listed among the islands receiving branch connections from Port Blair.