UPSC Physics

Notes:
Static friction is a self-adjusting force, matching the applied force up to its maximum limit. Sliding friction is the force when an object is moving and is always less than the limiting value of static friction. Rolling friction is always much smaller than sliding friction, not greater. Thus, only statements 1 and 2 are correct.

Notes:

• The Nobel Prize in Physics for 2022was awarded to John F. Clauser, Alain Aspect and Anton Zeilinger for their work in quantum mechanics by the Royal Swedish Academy of Sciences.
• In 2021, the Nobel Prize in Physics was awarded to Syukuro Manabe and Klaus Hasselmann (jointly)for their research on climate models and to Giorgio Parisi for his work on the interplay of disorder and fluctuations in physical systems.
• The Nobel Prize for 2022 in Physiology or medicine was awarded to Svante Pääbo for his research in the field of genomes of extinct hominins and human evolution.

Notes:

• The magnitude of the Sun’s solar activity is decreasing. This period of decreased solar activity is known as the Modern Grand Solar Minimum that will last from 2020 to 2053.
• Sunspots (some as large as 50,000 km in diameter) are areas that appear dark on the surface of the Sun (photosphere). They appear dark because they are cooler than other parts of the Sun’s surface.
• Sunspots are relatively cool because they form at areas where magnetic fields are particularly strong.
• 2020 marks the beginning of the 11^thsolar cycle. The beginning of a solar cycle is a solar minimum, or when the Sun has the sunspots and thus, least activity.
• The middle of the solar cycle is the solar maximum, or when the Sun has the most sunspots.
• Maunder Minimum: The last time such an event occurred was during the Maunder Minimum, from 1645 CE to 1710 CE. That period is a part of the Little Ice Age (from 1300 to around 1850), when Earth went through a series of elongated cold periods.
• During the Maunder Minimum, the solar irradiance went down by 0.22 % in 1710 CE when the period ended. This brought down the temperatures in the Northern Hemisphere, especially in Europe, by 1-1.5°C and led to frozen rivers, long cold winters and cold summers.

Notes:

• Each of the year’s full moon gets a nickname. Any full moon within the month of November is called a Beaver Moon. The Beaver Moon got its name because it falls at that time of the year when beavers are working continuously to build themselves dams for the winter.
• A total lunar eclipse occurs when the Earth casts its shadow completely over a full moon, blocking reflection of all direct sunlight from the lunar orb and dimming the color of the moon to a reddish hue, hence the term “blood moon.”
• This is only possible when the orbits of the Earth, moon and sun align so that the moon is directly behind Earth relative to the sun. Otherwise, the moon passes above or below Earth’s shadow because its orbit around Earth is usually tilted relative to Earth’s orbit about the sun.

Notes:

• Red dwarf stars are small, low-mass, dim, and cool stars, they are the most common and smallest in the universe.
• As they don’t radiate much light, it’s very tough to detect them with the naked eye from Earth.
• However, as red dwarfs are dimmer than other stars, it is easier to find exoplanets that surround them. Therefore, red dwarfs are a popular target for planet hunting.
• The habitable zone of red dwarf stars is closer to the star than stars like our sun, making it easier to observe potentially habitable planets.

Notes:
Trans-Neptunian Objects (TNOs) are celestial bodies that orbit the Sun beyond the orbit of Neptune. They are part of the Kuiper Belt, a region of the outer solar system that contains a multitude of icy objects. Here are brief descriptions of four notable TNOs:

• Pluto: Pluto is perhaps the most well-known Trans-Neptunian Object. It was classified as the ninth planet in our solar system until its reclassification as a dwarf planet in 2006. Pluto has a diverse terrain, including icy plains, mountains, and a heart-shaped feature called Tombaugh Regio. It has five known moons, with Charon being the largest.
• Eris: Eris is another significant TNO. It is slightly smaller than Pluto but is more massive. Its discovery in 2005 led to the reclassification of Pluto as a dwarf planet. Eris has a highly eccentric orbit and is known for its highly reflective surface, suggesting the presence of icy materials.
• Makemake: Makemake is a large TNO named after the creation deity of the Rapa Nui people of Easter Island. It was discovered in 2005 and is notable for its reddish surface color. Makemake has no known moons and has a thin atmosphere composed mainly of nitrogen.
• Haumea: Haumea is a peculiar TNO with an elongated, rugby-ball-like shape, making it one of the most unique objects in the solar system. It was discovered in 2004 and named after the Hawaiian goddess of fertility. Haumea has two known moons, Hi’iaka and Namaka, and its surface is covered in crystalline water ice.

These four TNOs represent the diverse characteristics and intriguing features found among the many objects that reside in the Kuiper Belt beyond the orbit of Neptune. They offer insights into the formation and evolution of our solar system and continue to be fascinating subjects of scientific study.

Notes:

• Nuclear fusion happens when two heavy atomic nuclei merge to form a lighter nucleus, releasing energy. Incorrect: Nuclear fusion involves the merging of light atomic nuclei (such as hydrogen isotopes deuterium and tritium) to form a heavier nucleus (helium), releasing a vast amount of energy. Unlike nuclear fission, fusion does not involve heavy nuclei.
• It requires extremely high temperatures to overcome electrostatic repulsion between nuclei. Correct: Fusion requires extremely high temperatures (over 100 million Kelvin) to overcome the Coulomb barrier, which is the electrostatic repulsion between positively charged nuclei.
• Fusion energy produces minimal long-lived radioactive waste, unlike fission. Incorrect: Unlike nuclear fission, fusion does not generate long-lived radioactive waste. The main byproduct of fusion is helium, which is non-radioactive. Although fusion reactions involving tritium can produce some radioactive materials, their half-life is much shorter than that of fission waste.

Notes:

• The Richter scale was developed by Charles Richter in 1935: The Richter scale was indeed developed by Charles Richter in 1935 to measure earthquake magnitude. However, it has largely been replaced by the Moment Magnitude Scale (Mw) for modern seismology, as Mw provides more accurate readings for large earthquakes.
• The moment magnitude scale (Mw) considers the area of the fault and the size of seismic waves: This is correct. Mw provides a more accurate measure for larger earthquakes than the Richter scale.
• The Modified Mercalli Intensity scale measures the intensity of an earthquake without considering the human perception: This is incorrect. The Modified Mercalli Intensity scale measures the intensity of an earthquake based on the human perception. It classifies earthquakes from I (not felt) to XII (total destruction).

Thus, only two statements are correct.

Notes:

1. Neutrino production is driven by nuclear fusion reactions in the core, not by opacity. Thus, changing opacity values does not directly affect neutrino production.
2. The discrepancies caused by iron opacity challenge our understanding of solar models, suggesting that element abundances may not be as predicted.
3. The radiation-convection zone boundary in the sun is indeed where iron opacity is tested, allowing us to understand how energy is transported throughout the star.
4. Opacity is crucial in modelling the structure and evolution of stars. Inaccurate opacity data can lead to erroneous predictions about galaxy structure and overall universe evolution.

Notes:
Satyendra Nath Bose developed new statistical laws for photons, giving rise to Bose–Einstein statistics. This work enabled the classification of particles called bosons. However, he did not independently derive Einstein’s photoelectric equation; this theory was developed solely by Einstein. Thus, only statements 1 and 2 are correct, while statement 3 is incorrect.