Physics

51. Recently, scientists observed the merger of giant ‘blackholes’ billion

Recently, scientists observed the merger of giant ‘blackholes’ billions of lightyears away from the Earth. What is the significance of this observation?

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Higgs boson particles' were detected.
'Gravitational waves' were detected.
Possibility of inter-galactic space travel through 'wormhole' was confirmed.
It enabled the scientists to understand 'singularity'.
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The correct option is B. The observation of the merger of giant black holes billions of lightyears away from Earth led to the first direct detection of gravitational waves.
Gravitational waves are ripples in the fabric of spacetime caused by accelerating massive objects. Highly energetic events like the merger of black holes or neutron stars are strong sources of gravitational waves.
The LIGO and Virgo collaborations detected the first direct evidence of gravitational waves in 2015 (event GW150914), which originated from the merger of two black holes. This observation was a landmark discovery, confirming a major prediction of Einstein’s general theory of relativity and opening a new window for observing the universe through gravitational wave astronomy.
A) Higgs boson particles were detected at the Large Hadron Collider (LHC) at CERN, which is unrelated to black hole mergers.
C) While black holes and general relativity are related to the concept of wormholes, the detection of gravitational waves from a merger does not confirm the possibility of inter-galactic space travel through wormholes.
D) Observing black hole mergers and the resulting gravitational waves provides insights into the nature of gravity in extreme conditions, but it does not directly enable scientists to understand the singularity at the heart of a black hole, which remains a theoretical concept under current physics.

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52. Consider the following phenomena : 1. Light is affected by gravity.

Consider the following phenomena :

  • 1. Light is affected by gravity.
  • 2. The Universe is constantly expanding.
  • 3. Matter warps its surrounding space-time.

Which of the above is/are the prediction/predictions of Albert Einstein’s General Theory of Relativity, often discussed in media ?

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1 and 2 only
3 only
1 and 3 only
1, 2 and 3
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Albert Einstein’s General Theory of Relativity describes gravity not as a force, but as a consequence of the curvature of spacetime caused by mass and energy. The theory makes several key predictions about the universe and gravity.
Statement 1 is correct. A prediction of General Relativity is that light is affected by gravity. Massive objects curve spacetime, and light follows this curvature. This phenomenon, known as gravitational lensing or the bending of light by gravity, was famously confirmed during a solar eclipse in 1919.
Statement 2 is correct. While Einstein initially favored a static universe, his field equations in General Relativity allow for dynamic solutions, including an expanding or contracting universe. The observation of the redshift of distant galaxies by Edwin Hubble in the 1920s provided strong evidence for an expanding universe, a phenomenon that is well-described by cosmological models based on General Relativity (like the Friedmann equations). Thus, the theory predicted the possibility of a non-static universe, which aligns with the observed expansion.
Statement 3 is correct. This is the fundamental principle of General Relativity: mass and energy warp the fabric of spacetime around them, and this warping is what we perceive as gravity.
All three statements describe predictions or fundamental aspects of Albert Einstein’s General Theory of Relativity that are often discussed in media and scientific discourse. Other predictions include gravitational time dilation, gravitational redshift, the precession of planetary orbits (like Mercury’s perihelion), and gravitational waves.

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53. The terms ‘Event Horizon’, ‘Singularity’, ‘String Theory’ and ‘Standar

The terms ‘Event Horizon’, ‘Singularity’, ‘String Theory’ and ‘Standard Model’ are sometimes seen in the news in the context of

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Observation and understanding of the Universe
Study of the solar and the lunar eclipses
Placing satellites in the orbit of the Earth
Origin and evolution of living organisms on the Earth
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The correct answer is A) Observation and understanding of the Universe.
‘Event Horizon’ and ‘Singularity’ are terms associated with black holes, phenomena extensively studied in astrophysics and cosmology, related to the structure and evolution of the Universe. ‘String Theory’ is a theoretical framework in physics attempting to describe the fundamental constituents of the universe as tiny vibrating strings, aiming for a unified theory of everything. The ‘Standard Model’ is a theory describing the fundamental particles and forces (excluding gravity) that make up the Universe and how they interact. All these terms belong to the fields of cosmology, astrophysics, and theoretical particle physics, which are dedicated to observing and understanding the fundamental nature and workings of the Universe.
While related to astronomy, eclipses (B) are specific celestial events and do not directly involve these fundamental concepts. Satellite placement (C) is related to orbital mechanics and space technology, not these theoretical physics terms. Origin and evolution of living organisms (D) is the domain of biology, genetics, and evolutionary science, which are unrelated to these concepts from physics/cosmology.

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54. With reference to ‘fuel cells’ in which hydrogen-rich fuel and oxygen

With reference to ‘fuel cells’ in which hydrogen-rich fuel and oxygen are used to generate electricity, consider the following statements :

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  • 1. If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products.
  • 2. Fuel cells can be used for powering buildings and not for small devices like laptop computers.
  • 3. Fuel cells produce electricity in the form of Alternating Current (AC).

Which of the statements given above is/are correct?

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1 only
2 and 3 only
1 and 3 only
1, 2 and 3
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UPSC IAS – 2015
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Only statement 1 is correct.
In a hydrogen fuel cell, hydrogen reacts with oxygen to produce electricity, water, and heat. This process is efficient and produces only water and heat as by-products when pure hydrogen is used.
Statement 2 is incorrect because fuel cells are highly scalable and can power everything from large buildings, vehicles, and grid-level energy storage to small devices like laptops and mobile phones. Statement 3 is incorrect because fuel cells generate Direct Current (DC) electricity. An inverter is required to convert the DC output to Alternating Current (AC) if needed for applications requiring AC.

55. In the context of modern scientific research, consider the following s

In the context of modern scientific research, consider the following statements about ‘IceCube’, a particle detector located at South Pole, which was recently in the news :

  • It is the world’s largest neutrino detector, encompassing a cubic kilometre of ice.
  • It is a powerful telescope to search for dark matter.
  • It is buried deep in the ice.

Which of the statements given above is/are correct?

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1 only
2 and 3 only
1 and 3 only
1, 2 and 3
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The correct option is C. Statements 1 and 3 about the IceCube particle detector are correct.
– Statement 1: IceCube is indeed the world’s largest neutrino detector. It consists of thousands of sensors embedded in a cubic kilometre of ice at the South Pole, designed to detect high-energy neutrinos.
– Statement 2: While neutrinos are fundamental particles relevant to various areas of physics, including cosmology and potential dark matter interactions, IceCube is primarily designed as a neutrino *telescope* to study astrophysical sources of high-energy neutrinos (like supernovae, gamma-ray bursts, active galactic nuclei). Searching for dark matter is not its primary or stated main purpose.
– Statement 3: The detector sensors (Digital Optical Modules or DOMs) are lowered into holes drilled deep into the Antarctic ice, at depths between 1450 and 2450 meters, making this statement correct.
By detecting the faint light (Cherenkov radiation) produced when neutrinos interact with the ice, IceCube scientists can infer the direction and energy of the neutrinos, opening a new window to observe the universe.

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56. The efforts to detect the existence of Higgs boson particle have becom

The efforts to detect the existence of Higgs boson particle have become frequent news in the recent past. What is/are the importance/importances of discovering this particle?

  • 1. It will enable us to understand as to why elementary particles have mass.
  • 2. It will enable us in the near future to develop the technology of transferring matter from one point to another without traversing the physical space between them.
  • 3. It will enable us to create better fuels for nuclear fission.

Select the correct answer using the codes given below.

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1 only
2 and 3 only
1 and 3 only
1, 2 and 3
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Statement 1 is correct because the Higgs boson is fundamentally linked to the mechanism by which elementary particles acquire mass through their interaction with the Higgs field. Statements 2 and 3 are incorrect; the discovery of the Higgs boson is not related to matter transfer technology (teleportation) or nuclear fission fuel development.
The Standard Model of particle physics describes the fundamental particles and forces. The Higgs field and its associated particle, the Higgs boson, were proposed to explain why some elementary particles have mass while others (like photons) do not. The detection of the Higgs boson in 2012 by the ATLAS and CMS experiments at CERN’s Large Hadron Collider confirmed this mechanism.
Statement 2 describes a speculative concept (teleportation) not related to the properties or applications of the Higgs boson. Statement 3 is irrelevant to the field of nuclear energy; nuclear fission involves the splitting of atomic nuclei, a process governed by the strong nuclear force and properties of isotopes, not the Higgs mechanism.

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57. The known forces of nature can be divided into four classes, viz., gra

The known forces of nature can be divided into four classes, viz., gravity, electromagnetism, weak nuclear force and strong nuclear force. With reference to them, which one of the following statements is not correct?

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Gravity is the strongest of the four
Electromagnetism acts only on particles with an electric charge
Weak nuclear force causes radioactivity
Strong nuclear force holds protons and neutrons inside the nucleus of an atom
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The statement that Gravity is the strongest of the four fundamental forces is not correct.
The four fundamental forces of nature are, in order of decreasing strength: Strong Nuclear Force, Electromagnetic Force, Weak Nuclear Force, and Gravity. Gravity is by far the weakest of the four forces. The Strong Nuclear Force holds the nucleus together, Electromagnetism governs interactions between charges, and the Weak Nuclear Force is involved in radioactive decay.
Although gravity is the weakest force at the particle level, its effects are cumulative and always attractive. This makes it the dominant force on large astronomical scales (planets, stars, galaxies). The relative strengths of the forces are approximately: Strong Nuclear Force ~ 1, Electromagnetic Force ~ 10⁻², Weak Nuclear Force ~ 10⁻⁶, Gravity ~ 10⁻³⁹ (relative to the strong force at typical nuclear scales).

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58. Rainbow is produced when sunlight falls on drops of rain. Which of the

Rainbow is produced when sunlight falls on drops of rain. Which of the following physical phenomena are responsible for this?

  • 1. Dispersion
  • 2. Refraction
  • 3. Internal reflection

Select the correct answer using the codes given below.

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1 and 2 only
2 and 3 only
1 and 3 only
1, 2 and 3
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Rainbow is produced when sunlight falls on drops of rain, and the phenomena responsible are dispersion, refraction, and internal reflection.
When sunlight enters a raindrop, it is refracted (bent). As the light enters, it also undergoes dispersion, splitting into its constituent colours because different wavelengths of light are refracted at slightly different angles. The dispersed light then reflects off the back inner surface of the raindrop (internal reflection). Finally, the light is refracted again as it exits the raindrop towards the observer. All three processes are essential for the formation of a rainbow.
Primary rainbows are formed by light undergoing one internal reflection. Secondary rainbows, which are fainter and appear above the primary rainbow with the colours reversed, are formed by light undergoing two internal reflections. In both cases, refraction and dispersion occur at the air-water interfaces.

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59. Consider the following phenomena : 1. Size of the sun at dusk 2. Co

Consider the following phenomena :

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  • 1. Size of the sun at dusk
  • 2. Colour of the sun at dawn
  • 3. Moon being visible at dawn
  • 4. Twinkle of stars in the sky
  • 5. Polestar being visible in the sky

Which of the above are optical illusions?

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1, 2 and 3
3, 4 and 5
1, 2 and 4
2, 3 and 5
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UPSC IAS – 2013
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The size of the sun at dusk, the colour of the sun at dawn, and the twinkle of stars in the sky are considered optical phenomena or illusions.
1. The apparent increase in the size of the sun (or moon) near the horizon (dusk) is an optical illusion known as the Moon illusion. 2. The reddish/orange colour of the sun at dawn is due to atmospheric scattering (Rayleigh scattering), where shorter wavelengths (blue/green) are scattered away more than longer wavelengths (red/orange) when light travels a longer path through the atmosphere. This phenomenon leads to a perceived colour change. 4. The twinkling of stars is caused by atmospheric refraction due to turbulence in the air, which makes the light from distant stars appear to fluctuate in brightness and position.
Phenomena 3 (Moon being visible at dawn) and 5 (Polestar being visible in the sky) are real astronomical occurrences related to the celestial positions of these bodies and are not optical illusions in the sense of being perceptual distortions or atmospheric effects causing altered appearance. Therefore, 1, 2, and 4 fit the description of optical illusions or related atmospheric optical phenomena causing altered visual perception.

60. Ball bearings are used in bicycles, cars, etc., because

Ball bearings are used in bicycles, cars, etc., because

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the actual area of contact between the wheel and axle is increased
the effective area of contact between the wheel and axle is increased
the effective area of contact between the wheel and axle is reduced
None of the above statements is correct
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Ball bearings are used in bicycles, cars, etc., because they significantly reduce the effective area of contact between the moving parts (like the wheel and axle), thereby reducing friction.
Ball bearings replace sliding friction with rolling friction. Sliding friction occurs over a larger contact area between the axle and its housing. Ball bearings consist of spherical balls rolling between two races. The contact between the balls and the races is nearly point contact (in theory, or a very small ellipse in practice). This reduces the area experiencing friction and, crucially, replaces high sliding friction with much lower rolling friction.
Rolling friction is generally much less than sliding friction for the same load. By allowing parts to roll over each other via the balls, the overall frictional force opposing motion is greatly reduced, making movement easier and more efficient, and reducing wear and tear.

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