Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Domestic electrical wiring is primarily a parallel connection, meaning that appliances and devices are connected in parallel to the power supply. This ensures that each device receives the same voltage, and turning one device on or off does not affect the others. Parallel wiring also allows for individual control of appliances and prevents overloading of a single circuit. In a series connection, devices share the same current, and the total resistance adds up, which can cause voltage drops, as seen in old-fashioned Christmas lights where if one bulb fails, the entire string goes out.

Explanation

The industrial ages gave us the understanding of sunlight as an energy source. India is endowed with vast solar energy potential. About 5,000 trillion kWh per year energy is incident over India’s land area with most parts receiving 4-7 kWh per sqm per day. Solar photovoltaic power can effectively be harnessed providing huge scalability in India.

Statement 1 is correct: Solar water heaters are widely used for residential purposes.

Statement 2 is correct: Solar-powered pumps are increasingly utilized for small-scale irrigation. Governments under PM KUSUM are advocating for proliferation of such pumps.

Statement 3 is correct: Solar street lights are common in both rural and urban areas.

Statement 4 is correct: Solar microgrids and standalone systems can provide electricity to remote villages and small towns.

Explanation

Statement 1 is correct: In space, there is no atmosphere to scatter sunlight, so the sky appears black, even during the day.

Statement 2 is correct: In space, stars appear as steady points of light because there is no atmospheric turbulence to cause them to twinkle, as we observe from Earth.

Statement 3 is correct: Space near the Sun is extremely hot, with temperatures rising significantly when exposed to direct sunlight. The spacecraft would experience extreme temperatures, which is why temperature regulation inside the spacecraft is essential for astronauts.

Explanation

An alpha particle consists of two protons and two neutrons, which is exactly the nucleus of a helium atom (He2+). The mass of an alpha particle is very close to the mass of a helium atom as the mass of electrons is insignificant in comparison with protons and neutrons.

Explanation

Option (b) is correct: Chromium is added to iron to produce stainless steel and other high-performance alloys. It provides resistance to oxidation and high temperatures while also increasing hardness and abrasion resistance. Chromium’s ability to form a protective oxide layer makes it essential for producing steel that can withstand harsh conditions. Options (a), (c) and (d) are incorrect:

Aluminium is used for lightweight and corrosion-resistant alloys but not for high-temperature or abrasion resistance. Nickel primarily enhances toughness and corrosion resistance but does not directly improve abrasion resistance as much as chromium. Tungsten contributes to high-temperature strength and wear resistance, especially in tool steels, but chromium is the primary alloying element for the application.

Explanation

Micronutrients are essential elements required by plants in very small quantities (typically less than 100 mg/ kg of plant dry matter). Despite their minimal requirement, these nutrients play a critical role in various physiological and biochemical processes necessary for plant growth and development. Sodium is not considered an essential micronutrient for most plants. It may play a role in some specific plants, such as C₄ plants, but it is not universally required as a micronutrient. Other important micronutrients are Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), Chlorine (Cl), Nickel (Ni).

Explanation

Option (d) is correct: Methyl alcohol (methanol) is a highly toxic substance that is sometimes illegally added to liquor to reduce costs. Once consumed, it metabolizes into formaldehyde and formic acid, causing blindness, organ failure, or death. Symptoms of methanol poisoning include blurred vision, nausea, and seizures. Options (a), (b) and (c) are incorrect:

Ethyl alcohol is commonly known as ethanol, it is the primary component in alcoholic beverages and is safe for consumption in moderate amounts. Amyl alcohol is found in some industrial applications, amyl alcohol is rarely used in adulterated liquor due to its cost and limited availability. Benzyl alcohol is a non-toxic solvent and not associated with blindness in liquor tragedies. It is used in pharmaceuticals and cosmetics.

Explanation

The physico-chemical characteristics of water in water sources are primarily affected by effluents discharged from various sources, including industries, sewage, and agricultural runoff. Effluents introduce pollutants like organic matter, chemicals, heavy metals, and nutrients into water bodies, leading to significant changes in water quality. How Effluents cause Changes:

Chemical Changes: Effluents can alter the pH, increase the concentration of harmful chemicals, and introduce toxic substances. Nutrient Loading: Excessive nutrients (like nitrates and phosphates) from effluents can cause eutrophication, leading to algal blooms. Dissolved Oxygen Levels: Organic pollutants increase the Biological Oxygen Demand (BOD), reducing dissolved oxygen levels and harming aquatic life. Turbidity and Color: Effluents can increase turbidity, reduce light penetration, and alter the color of the water.

Explanation

Living organisms require a variety of elements for various physiological functions. Among these, certain elements are required in major quantities (also known as macronutrients). The elements potassium (K), sodium (Na), magnesium (Mg), and calcium (Ca) are macronutrients required in relatively large amounts by living organisms:

Potassium (K) is vital for cell function, maintaining osmotic balance, and nerve transmission. Sodium (Na) is important for maintaining osmotic pressure and fluid balance, as well for nerve function. Magnesium (Mg) is essential for photosynthesis in plants, enzyme function, and the structural component of bones in animals. Calcium (Ca) is crucial for bone and teeth formation, muscle contraction, blood clotting, and nerve function.

Explanation

Seedless tomatoes can be produced through a process called parthenocarpy where fruits develop without fertilization and thus contain no seeds. This is achieved by spraying hormones like gibberellins or auxins on the flowers of the tomato plants. These hormones promote fruit development without the need for fertilization leading to seedless fruits.