Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

A black hole is a region in space where gravity is so intense that not even light or any form of radiation can escape from it. This extreme gravitational pull is a result of its very high density, as the mass of the black hole is compressed into a very small volume, creating a gravitational field strong enough to trap light and radiation. Event Horizon: The boundary around a black hole beyond which nothing, not even light, can escape due to the extreme gravitational pull. Singularity: The point at the center of a black hole where gravity is infinitely strong, and matter is thought to be crushed to an infinitely small point with infinite density. Schwarzschild Radius: The radius of the event horizon, which depends on the mass of the black hole. It defines the size of the black hole’s event horizon. Accretion Disk: A rotating disk of matter, such as gas and dust, that orbits a black hole. The matter in the disk heats up as it spirals toward the event horizon. Hawking Radiation: A theoretical prediction by physicist Stephen Hawking that black holes can emit radiation due to quantum effects near the event horizon, eventually leading to their slow evaporation.

Explanation

Explosions in mines are often caused by the presence of methane gas, which mixes with air to form an explosive mixture. This phenomenon is known as a "firedamp explosion." Methane is highly flammable and can ignite when exposed to a spark or heat, leading to devastating consequences in mining environments.

Explanation

Nichrome is an alloy of nickel and chromium, often used in heating elements due to its high resistance to heat and corrosion. It is ductile, allowing it to be drawn into wires for use in various applications. It is considered hard relative to other ductile materials, which is why it finds applications in industrial heating where both durability and flexibility are important. Options (a), (b) and (c) are incorrect:

Carborundum (silicon carbide) is very hard but not ductile; it is brittle. It is mainly used as an abrasive material. Cast iron is hard but brittle, and it cannot undergo significant deformation without breaking. While Tungsten is harder, it is less ductile compared to Nichrome in practical scenarios. Tungsten’s brittleness increases under certain conditions, making Nichrome a more balanced choice for being both hard and ductile.

Explanation

Statement 1 is correct: Hard water, rich in calcium and magnesium, can contribute to dietary intake of these minerals, but prolonged consumption may lead to kidney stones and urinary tract issues, particularly for susceptible individuals. Research indicates that high calcium levels can affect renal function.

Statement 2 is correct: When hard water is used with soap, it forms soap scum, which reduces lather and makes washing less effective. Scum leaves residue on clothes, making them feel rough and unclean. This can also increase detergent usage.

Statement 3 is correct: The minerals in hard water like calcium carbonate and magnesium salts, form scale in boilers and pipes, reducing thermal efficiency and leading to energy wastage and equipment failure.

Statement 4 is correct: Continuous irrigation with hard water results in soil salinization, decreasing permeability and crop yield. Excess minerals like calcium and magnesium hinder plant nutrient absorption due to reduced soil’s permeability. Directions: The following two Items consist of statements. One labeled as the ‘Assertion (A)’ and the other as ‘Reason (R)’. You have to answer these items using the code given below: (1999)

Explanation

A is matched with 2: Cracking is a process in the petroleum industry where large hydrocarbons are broken into smaller hydrocarbons like gasoline and diesel. B is matched with 3:Smelting is used in the copper industry to extract metal from its ore by heating it in a furnace. C is matched with 4: Hydrogenation is used in the production of edible fats by adding hydrogen to vegetable oils, converting them into margarine or vanaspati. D is matched with 1: Vulcanization is a process in the rubber industry where sulfur is added to raw rubber to improve its elasticity and strength.

Explanation

Blue-green algae, also known as cyanobacteria are often used as biofertilizers in rice cultivation. They have the ability to fix atmospheric nitrogen into a form that plants can use, enriching the soil with nitrogen and improving crop growth.

Explanation

A phytotron is a facility that provides an environment where various environmental factors such as temperature, humidity, light, and CO₂ levels can be controlled precisely to study plant growth and development. This setup helps scientists to conduct experiments on plants in a controlled and reproducible environment. Phytotron is neither related with growing plants in disease free conditions nor conserving endangered species of plants.

Explanation

Soft drinks, especially colas, often contain caffeine, which is a stimulant. Caffeine can help to increase alertness and reduce fatigue, and it is commonly added to colas and other energy drinks.

Explanation

Canola oil is derived from a type of mustard plant that has been specially bred to have very low levels of erucic acid, which is a substance that can be harmful in large amounts. This makes canola oil safe and suitable for human consumption. Canola oil is known for being rich in unsaturated fatty acids, especially omega-3 and omega-6 fatty acids, making it a heart-healthy cooking oil. It has a long shelf life due to its stability, and its mild flavor makes it suitable for a variety of culinary uses.

Explanation

Assertion (A) is false: Humans have 46 chromosomes (23 pairs), one of which determines sex. This pair consists of XX in females and XY in males. During reproduction, the mother always contributes an X chromosome, while the father can contribute either an X or a Y chromosome. If a sperm carrying an X chromosome fertilizes the egg, the offspring will be female (XX), whereas if a sperm carrying a Y chromosome fertilizes the egg, the offspring will be male (XY). Since the sperm determines the final chromosomal combination, the father plays the major role in sex determination. Reason (R) is true: Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).