UPSC CDS-2

41. A person is standing on a frictionless horizontal ground. How can he m

A person is standing on a frictionless horizontal ground. How can he move by a certain distance on this ground?

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By sneezing
By jumping
By running
By rolling
This question was previously asked in
UPSC CDS-2 – 2017
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The correct option is A) By sneezing.
On a frictionless horizontal surface, a person cannot propel themselves forward by pushing against the ground (like walking, running, or jumping) because there is no friction to provide an external reaction force in the horizontal direction. However, by sneezing, the person expels air in one direction. According to Newton’s third law of motion, this action creates an equal and opposite reaction force on the person’s body, propelling them in the opposite direction of the expelled air.
This is a classic physics problem illustrating Newton’s laws of motion, particularly the conservation of momentum. In the absence of external forces (friction), the total momentum of the person-air system remains constant. If the person expels air with a certain momentum, their body must acquire an equal and opposite momentum to conserve the total momentum (initially zero).

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42. After using for some time, big transformers get heated up. This is due

After using for some time, big transformers get heated up. This is due to the fact that

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  • 1. current produces heat in the transformers
  • 2. hysteresis loss occurs in the transformers
  • 3. liquid used for cooling gets heated

Select the correct answer using the code given below.

1 only
2 and 3 only
1 and 2 only
1, 2 and 3
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UPSC CDS-2 – 2017
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Transformers get heated up due to current producing heat in the windings (copper loss), hysteresis loss in the core, and the liquid used for cooling getting heated as it absorbs these losses.
The main reasons for heating in a transformer are power losses occurring during its operation. These include copper losses (I²R losses) in the windings due to the resistance of the copper wires, and iron losses (core losses) in the core material. Iron losses consist of hysteresis loss (energy dissipated due to the repeated magnetization and demagnetization of the core by the alternating magnetic field) and eddy current loss (induced circulating currents in the core causing resistive heating). Statement 1 correctly identifies copper loss. Statement 2 correctly identifies hysteresis loss, which is one component of iron loss.
Large transformers often use oil or other liquids for cooling. This liquid absorbs the heat generated by the copper and iron losses and circulates, allowing the heat to be dissipated, usually through radiators. The fact that the liquid gets heated (Statement 3) is a direct consequence of the heat generated by losses (1 and 2, plus eddy currents) being transferred to the coolant. While not a primary *source* of heat generation like 1 and 2, the heating of the cooling liquid is an integral part of the thermal behavior and the overall “heated up” state of a large, operating transformer. Thus, all three facts listed contribute to understanding why big transformers get heated up.

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43. Infrared, visible and ultraviolet radiations/ light have different pro

Infrared, visible and ultraviolet radiations/ light have different properties. Which one of the following statements related to these radiations/light is not correct?

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The wavelength of infrared is more than that of ultraviolet radiation.
The wavelength of ultraviolet is smaller than that of visible light.
The photon energy of visible light is more than that of infrared light.
The photon energy of ultraviolet is lesser than that of visible light.
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UPSC CDS-2 – 2017
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The statement “The photon energy of ultraviolet is lesser than that of visible light” is not correct.
Electromagnetic radiations are ordered by their frequency or wavelength. In order of increasing energy (and frequency, and decreasing wavelength), the spectrum goes from Infrared (IR) to Visible light to Ultraviolet (UV). Photon energy is directly proportional to frequency (E = hf) and inversely proportional to wavelength (E = hc/λ). Therefore, UV radiation has higher frequency, higher photon energy, and shorter wavelength compared to visible light and infrared radiation.
Statement A is correct because IR has a longer wavelength than UV. Statement B is correct because UV has a shorter wavelength than visible light. Statement C is correct because visible light has higher energy than IR. Statement D claims UV energy is lesser than visible light energy, which is false; UV energy is higher than visible light energy.

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44. A ray of light is incident on a plane mirror at an angle of 40° with r

A ray of light is incident on a plane mirror at an angle of 40° with respect to normal. When it gets reflected from the mirror, it undergoes a deviation of

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40°
100°
90°
80°
This question was previously asked in
UPSC CDS-2 – 2017
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When a ray of light is incident on a plane mirror at an angle of 40° with respect to normal, it undergoes a deviation of 80°.
According to the law of reflection, the angle of incidence (i) is equal to the angle of reflection (r), and both are measured with respect to the normal to the mirror surface. Given i = 40°, then r = 40°. Deviation is the angle between the direction of the incident ray and the direction of the reflected ray. If the incident ray were not reflected, it would continue in a straight line. The reflection changes its direction.
The angle between the incident ray and the normal is 40°. The angle between the reflected ray and the normal is 40° on the opposite side of the normal. The total angle between the incident ray and the reflected ray is the sum of the angle between the incident ray and the normal and the angle between the normal and the reflected ray in the plane of reflection, which is 40° + 40° = 80°. This angle represents the deviation of the ray from its original path. Alternatively, the angle between the incident ray and the mirror surface is θ = 90° – i = 90° – 40° = 50°. The angle of deviation (δ) for reflection from a plane mirror is also given by δ = 180° – 2θ = 180° – 2(50°) = 180° – 100° = 80°.

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45. Two wires are made having same length l and area of cross-section A. W

Two wires are made having same length l and area of cross-section A. Wire 1 is made of copper and wire 2 is made of aluminium. It is given that the electrical conductivity of copper is more than that of aluminium. In this context, which one of the following statements is correct?

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The resistance of wire 1 will be higher than that of wire 2.
The resistance of wire 2 will be higher than that of wire 1.
The resistance of both the wires will be the same.
If same current is flown through both the wires, the power dissipated in both the wires will be the same.
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The resistance of wire 2 will be higher than that of wire 1.
The resistance (R) of a wire is inversely proportional to its electrical conductivity (σ) for a given length (l) and area of cross-section (A). The formula is R = (1/σ) * (l/A). Since both wires have the same length and area of cross-section, their resistances are directly proportional to their resistivities (ρ = 1/σ). We are given that the electrical conductivity of copper (wire 1) is more than that of aluminium (wire 2), i.e., σ_Cu > σ_Al. This implies that the resistivity of copper is less than that of aluminium (ρ_Cu < ρ_Al).
Since R = ρ * (l/A) and l and A are the same for both wires, R is proportional to ρ. As ρ_Cu < ρ_Al, it follows that R_1 (copper) < R_2 (aluminium). Therefore, the resistance of wire 2 (aluminium) is higher than that of wire 1 (copper). Power dissipated is given by P = I²R or P = V²/R. If the same current flows, power dissipated is proportional to resistance. If the same voltage is applied, power dissipated is inversely proportional to resistance.

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46. An electron and a proton starting from rest are accelerated through a

An electron and a proton starting from rest are accelerated through a potential difference of 1000 V. Which one of the following statements in this regard is correct?

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The kinetic energy of both the particles will be different.
The speed of the electron will be higher than that of the proton.
The speed of the proton will be higher than that of the electron.
The speed of the electron and the proton will be equal.
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UPSC CDS-2 – 2017
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The speed of the electron will be higher than that of the proton.
When an electron and a proton, both starting from rest, are accelerated through the same potential difference V, they gain the same kinetic energy (KE). The kinetic energy gained is equal to the work done by the electric field, which is qV, where q is the charge of the particle and V is the potential difference. The magnitude of charge is the same for both electron and proton (|q_e| = |q_p|). So, KE_electron = KE_proton = |q|V.
Kinetic energy is given by KE = 1/2 * mv², where m is the mass and v is the speed. Since KE is the same for both particles, and the mass of the electron (m_e) is significantly less than the mass of the proton (m_p) (m_e ≈ m_p/1836), for the equation 1/2 * m_e * v_e² = 1/2 * m_p * v_p² to hold, the velocity of the lighter particle (electron) must be greater than the velocity of the heavier particle (proton). Thus, v_e > v_p.

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47. A biological community in its environment such as a pond, an ocean, a

A biological community in its environment such as a pond, an ocean, a forest, even an aquarium is known as

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biome
community
abiotic environment
ecosystem
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A biological community in its environment such as a pond, an ocean, a forest, even an aquarium is known as an ecosystem.
An ecosystem is defined as a community of living organisms (biotic components) interacting with the nonliving components (abiotic components) of their environment. The examples given (pond, ocean, forest, aquarium) all represent systems where plants, animals, and other organisms live and interact with physical and chemical factors like water, soil, air, and sunlight.
A community refers specifically to the interacting group of different species in a particular area. A biome is a large geographical region characterized by specific climate and ecological features. The abiotic environment refers only to the non-living parts. The definition provided in the question accurately describes an ecosystem, encompassing both the biotic community and its abiotic environment.

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48. Pearl is a hard object produced within the soft tissues of a mollusk.

Pearl is a hard object produced within the soft tissues of a mollusk. Which one of the following is the main constituent of pearl?

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Calcium carbonate
Calcium oxide
Calcium nitrate
Calcium sulphate
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UPSC CDS-2 – 2017
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The main constituent of pearl is calcium carbonate.
Pearls are formed within mollusks when an irritant, such as a parasite or a piece of shell, enters the shell. The mollusk secretes layers of nacre (mother-of-pearl) around the irritant as a defense mechanism. Nacre is composed primarily of microscopic crystals of calcium carbonate (CaCO3), mainly in the aragonite form, cemented together by an organic protein matrix called conchiolin.
The calcium carbonate layers combined with the organic matrix create the iridescent luster characteristic of pearls. The quality and value of a pearl depend on factors like size, shape, color, luster, surface quality, and nacre thickness.

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49. Human insulin molecule is composed of one α-chain having 21 amino acid

Human insulin molecule is composed of one α-chain having 21 amino acids and one β-chain having 30 amino acids. How many functional insulin genes occur in adult humans?

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One
Two
Three
Four
This question was previously asked in
UPSC CDS-2 – 2017
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There are two functional insulin genes in adult humans.
The gene encoding human insulin, INS, is located on chromosome 11. Humans are diploid organisms, meaning they have two sets of chromosomes (except for sex chromosomes in males). Therefore, a healthy individual has two copies of the INS gene, one on each of the homologous chromosome 11 pair. Both copies are typically functional, encoding the proinsulin precursor that is cleaved to form mature insulin.
Mutations in the INS gene can lead to various forms of diabetes, such as Maturity Onset Diabetes of the Young type 1 (MODY1). The structure of the insulin molecule, composed of alpha and beta chains linked by disulfide bonds, is derived from a single proinsulin polypeptide chain.

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50. Match List-I with List-II and select the correct answer using the code

Match List-I with List-II and select the correct answer using the code given below the Lists :

List-I
(Cell Organelle)		 List-II
(Function)
A. Mitochondria 1. Photosynthesis
B. Chloroplast 2. Protein synthesis
C. Ribosomes 3. Intracellular digestion
D. Lysosomes 4. ATP formation

Code :

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A-3, B-1, C-2, D-4
A-2, B-1, C-4, D-3
A-4, B-1, C-2, D-3
A-4, B-2, C-1, D-3
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UPSC CDS-2 – 2017
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The correct match is A-4, B-1, C-2, D-3.
Mitochondria are known as the powerhouses of the cell because they are the primary sites of cellular respiration, generating ATP. Chloroplasts are organelles found in plant cells and algae where photosynthesis takes place. Ribosomes are responsible for protein synthesis. Lysosomes contain hydrolytic enzymes that break down waste materials and cellular debris through intracellular digestion.
This question tests basic knowledge of the functions of major eukaryotic cell organelles. Understanding the primary role of each organelle is fundamental in biology.

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