Current Affairs MCQs – Page 48 (Q471-480)

Nitrogen is the most abundant gas in the Earth's atmosphere, making up roughly 78 percent of the air we breathe, far more than oxygen, which accounts for about 21 percent. Despite its abundance, most living organisms cannot use atmospheric nitrogen directly and instead rely on nitrogen-fixing bacteria to convert it into usable forms. Carbon dioxide, oxygen and argon are tempting distractors, with oxygen being the second most abundant atmospheric gas and carbon dioxide and argon present only in much smaller trace amounts. Nitrogen gas is relatively inert, meaning it does not readily react with other substances under normal atmospheric conditions.

The chemical formula for water is H2O, indicating that each molecule consists of two hydrogen atoms bonded to a single oxygen atom, one of the simplest yet most essential compounds for life on Earth. Water's unique properties, including its ability to dissolve many substances and its unusual behavior of expanding when frozen, make it critical to countless biological and geological processes. CO2, NaCl and O2 are tempting distractors, representing carbon dioxide, table salt and oxygen gas respectively, all common compounds but distinct from water. Roughly 71 percent of the Earth's surface is covered by water, mostly in the form of oceans.

The SI unit of force is the newton, named in honor of Sir Isaac Newton, defined as the force needed to accelerate a one-kilogram mass at a rate of one metre per second squared. This unit is fundamental to classical mechanics and appears throughout physics and engineering calculations involving force, weight and motion. Pascal, joule and watt are tempting distractors, representing the SI units of pressure, energy and power respectively, each closely related to but distinct from force. Newton's own laws of motion, published in his 1687 Principia Mathematica, form the theoretical basis for this unit that bears his name.

The SI unit of energy is the joule, named after English physicist James Prescott Joule, who conducted pioneering experiments establishing the relationship between heat, work and mechanical energy in the 19th century. One joule is defined as the amount of energy transferred when a force of one newton moves an object a distance of one metre. Watt, ohm and newton are tempting distractors, representing the SI units of power, electrical resistance and force respectively, each related to but distinct from energy. Joule's experiments helped establish the law of conservation of energy, a cornerstone principle of modern physics.

The SI unit of power is the watt, named after Scottish engineer James Watt, whose improvements to the steam engine helped drive the Industrial Revolution, defined as one joule of energy transferred or converted per second. Power measures the rate at which work is done or energy is transferred, distinguishing it from energy itself, which measures a total quantity. Volt, newton and joule are tempting distractors, representing the SI units of electric potential, force and energy respectively, each related to but distinct from power. Everyday electrical appliances are commonly rated in watts or kilowatts to indicate their rate of energy consumption.

The SI unit of electric current is the ampere, often shortened to amp, named after French physicist Andre-Marie Ampere, a pioneer in the study of electromagnetism in the early 19th century. One ampere is defined as the flow of a specific number of electric charges per second past a given point in a circuit. Volt, ohm and watt are tempting distractors, representing the SI units of electric potential, resistance and power respectively, each closely related to but distinct from current. Household electrical devices and circuit breakers are commonly rated in amperes to indicate the maximum current they can safely handle.

The SI base unit of thermodynamic temperature is the kelvin, named after Scottish physicist Lord Kelvin, who developed the concept of an absolute temperature scale beginning at absolute zero, the theoretical point at which all molecular motion stops. Unlike Celsius or Fahrenheit, the Kelvin scale does not use the degree symbol and is essential in scientific contexts requiring precise temperature measurement. Celsius, Rankine and Fahrenheit are tempting distractors, as each is a different temperature scale used in various contexts, with Rankine being an absolute scale used mainly in some American engineering fields. Absolute zero occurs at 0 Kelvin, equivalent to about minus 273.15 degrees Celsius.

The SI unit of pressure is the pascal, named after French mathematician and physicist Blaise Pascal, who conducted important early experiments on fluid pressure and vacuums. One pascal is defined as one newton of force applied over an area of one square metre, a relatively small unit often expressed in kilopascals for practical measurements like atmospheric pressure. Newton, joule and bar are tempting distractors, with bar being another common, though non-SI, unit of pressure often used in meteorology. Standard atmospheric pressure at sea level is approximately 101,325 pascals, or roughly 1013 hectopascals.

The SI unit of frequency is the hertz, named after German physicist Heinrich Hertz, who was the first to conclusively demonstrate the existence of electromagnetic waves in the 1880s, confirming James Clerk Maxwell's earlier theoretical predictions. One hertz represents one cycle or oscillation per second, a unit used to measure everything from sound waves to radio frequencies and computer processor speeds. Ohm, watt and decibel are tempting distractors, representing electrical resistance, power and sound intensity level respectively, each distinct from frequency. Human hearing typically ranges from about 20 hertz to 20,000 hertz, defining the audible sound spectrum.

The speed of light in a vacuum is approximately 300,000 kilometres per second, or more precisely about 299,792 kilometres per second, a fundamental constant of physics central to Einstein's theory of relativity. Nothing with mass can travel faster than this speed, a limit that has profound implications for our understanding of space, time and causality. 450,000, 600,000 and 150,000 kilometres per second are close numerical distractors designed to test precise knowledge of the actual figure. Light from the Sun takes about eight minutes to reach the Earth, meaning we always see the Sun slightly as it appeared moments in the past.