66th Prelims Re 2021

Explanation:

Electric current is a fundamental physical quantity in the International System of Units (SI) and is measured in amperes (A). It represents the flow of electric charge per unit of time. Force, velocity, and work are derived quantities: Force = mass × acceleration, Velocity = rate of change of displacement, Work = force × displacement.

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Sound waves are longitudinal waves where particles of the medium vibrate parallel to the direction of wave propagation. Radio waves, X-rays, and gamma rays are electromagnetic (transverse) waves, oscillating perpendicular to the direction of wave travel.

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Dispersion occurs when white light passes through a prism, separating into its constituent colors due to different wavelengths bending at different angles. Convex and concave lenses refract light but do not disperse it. Mirrors only reflect light.

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The temperature where Celsius and Fahrenheit are equal is -40°. Using the formula F = (9/5)C + 32 and solving for C when F = C gives C = -40°.

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Lens power is measured in dioptres (D), representing the reciprocal of the focal length in meters. Watt measures electrical power, Ampere measures electric current, and Volt measures electric potential difference.

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MRI uses strong magnetic fields and radio waves to generate images of internal body structures. X-rays are not used in MRI; they are used in radiography and CT scans.

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Frequency remains constant when sound transitions between media, determining the pitch. Wavelength and speed change according to the medium, while amplitude can also vary due to energy absorption.

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A light year measures distance, representing how far light travels in one year. It is commonly used in astronomy. It is not a measure of time, speed, or force.

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A neutron has no electric charge and is found in the atomic nucleus. Alpha particles are positively charged, electrons are negatively charged, and protons are positively charged.

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Resistivity, indicating how strongly a material opposes current, is measured in ohm-meters (Ω·m). Resistance is measured in ohms, conductance in siemens, and charge in coulombs.

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Sapphire, a variety of corundum, has the chemical formula Al2O3. Trace elements like chromium give it a red color, called ruby. Other formulas represent incorrect compounds.

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The octane number measures petrol's resistance to knocking in engines. Cetane number applies to diesel fuel, Reynolds number is for fluid dynamics, and butane number is not standard.

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Boron has the highest melting point (~2076°C) due to strong covalent bonds. Iron melts at ~1538°C, silicon at ~1414°C, and aluminium at ~660°C.

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Penicillin is an antibiotic effective against bacterial infections. Aspirin and Paracetamol are analgesics/antipyretics, and Chloroquine is an antimalarial drug.

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Compressed natural gas (CNG) primarily consists of methane (CH4). It is a cleaner fuel alternative for vehicles, producing lower emissions than petrol or diesel.

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Acid rain contains sulfuric acid (H2SO4) and nitric acid (HNO3), formed from atmospheric sulfur and nitrogen oxides reacting with water. CO2 contributes to mild acidity but is not a primary acid in acid rain.

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Heavy water contains deuterium instead of normal hydrogen, giving the formula D2O. It is used in nuclear reactors and has slightly different physical properties from H2O.

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Pure water is neutral with a pH of 7. Values below 7 indicate acidity, above 7 indicate alkalinity. The pH scale ranges from 0 to 14.

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The 2019 Nobel Prize in Chemistry was awarded to Goodenough, Whittingham, and Yoshino for developing lithium-ion batteries, which are rechargeable and widely used in electronics and electric vehicles.

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Natural rubber is polyisoprene, formed by polymerizing isoprene units (C5H8). Vinyl acetate forms PVA, styrene forms polystyrene, and propene forms polypropylene.

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Copper sulphate is used as a fungicide and algaecide in water tanks. Nitric acid, zinc sulphate, and magnesium sulphate have other uses and are not commonly used to remove fungi.

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Chlorophyll contains carbon, hydrogen, and magnesium (central atom), but calcium is not a component.

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Xylem transports water and minerals from roots to leaves. Phloem transports nutrients, epidermis protects, and cambium contributes to growth in thickness.

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Green plants absorb carbon dioxide (CO2) during photosynthesis to produce glucose and oxygen. They release oxygen rather than absorb it.

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Kerosene is a hydrocarbon (C and H only) and contains no oxygen. Glass, soil, and cement all contain oxygen.

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Lipase is produced by the pancreas and helps in the digestion of fats in the small intestine.

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The BCG (Bacillus Calmette-Guérin) vaccine protects primarily against tuberculosis. It is given to infants in countries with high TB prevalence.

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Insulin is produced by the beta cells of the pancreas and regulates blood sugar levels. Thyroxine is from the thyroid, Galanin is a neuropeptide, and Gastrin is from the stomach.

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Lymphocytes, part of the lymphatic system, help return excess fluid from tissues to the bloodstream, contributing to circulation. Erythrocytes carry oxygen, platelets aid clotting, monocytes are immune cells.

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Angora wool is obtained from Angora rabbits. Goat wool gives cashmere/mohair, sheep give regular wool, and foxes do not produce usable wool.