General Science MCQs – Page 2 (Q11-20)

Electric current is measured in amperes (A), commonly shortened to amps, named after French physicist Andre-Marie Ampere, a pioneer of electromagnetism. One ampere represents a flow of about 6.24 quintillion electrons past a point per second, or formally one coulomb of charge per second. Current is closely tied to voltage (measured in volts) and resistance (measured in ohms) through Ohm's law, V = IR. Household circuit breakers are rated in amperes to prevent wires from overheating due to excessive current.

Temperature on the absolute scale is measured in kelvin (K), named after Lord Kelvin, who proposed the concept of absolute zero, the theoretical point where all molecular motion stops. Absolute zero equals 0 K, or minus 273.15 degrees Celsius, and has never been reached experimentally though scientists have gotten extremely close in laboratory conditions. Unlike Celsius or Fahrenheit, the kelvin scale has no negative values, which makes it essential in physics and chemistry calculations such as the ideal gas law. Kelvin degrees are the same size as Celsius degrees.

The amount of substance is measured in moles (mol), a unit that counts particles such as atoms or molecules using Avogadro's number, approximately 6.022 times ten to the 23rd particles per mole. This unit lets chemists relate the microscopic world of atoms to measurable, macroscopic quantities like grams, since one mole of any substance has a mass in grams equal to its molecular weight. The mole is essential for balancing chemical equations and calculating reactant and product quantities in reactions. It was named in 1902 from the German word Molekul.

Luminous intensity is measured in candela (cd), a unit originally based on the light emitted by a standard candle before being redefined using precise physical constants tied to a specific frequency of light. It differs from the lumen, which measures total visible light output from a source in all directions, and the lux, which measures illuminance, or how much light falls on a given surface area. The candela remains one of the seven SI base units and is important in designing lighting for safety and visibility standards.

Earth's gravitational acceleration is approximately 9.8 meters per second squared, meaning a falling object's speed increases by about 9.8 m/s for every second it falls, ignoring air resistance. This value varies slightly across the globe due to Earth's shape, rotation, and local geology, ranging from about 9.78 m/s squared at the equator to 9.83 m/s squared near the poles. Galileo is credited with first demonstrating that objects of different masses fall at the same rate in a vacuum, a principle later confirmed dramatically during Apollo 15's hammer-and-feather experiment on the Moon.

Kinetic energy, the energy of motion, is calculated as one-half times mass times velocity squared (KE = 1/2 mv squared), showing that energy increases with the square of speed rather than linearly. This means doubling an object's speed quadruples its kinetic energy, which is why high-speed collisions are so much more destructive than slow ones. Kinetic energy contrasts with potential energy, which is stored energy due to position, such as gravitational potential energy. The total mechanical energy of a system, kinetic plus potential, remains constant when only conservative forces act.

Gravitational potential energy is calculated as mass times gravitational acceleration times height (PE = mgh), representing the energy an object has due to its position above a reference point. This stored energy converts into kinetic energy as an object falls, which is the principle behind hydroelectric dams that release stored water to generate electricity. The higher and heavier an object, the more potential energy it possesses, which is why roller coasters gain the most speed after the tallest drops. This concept is central to the law of conservation of mechanical energy.

A see-saw is a classic example of a lever, one of the six classical simple machines identified since antiquity, consisting of a rigid bar that pivots around a fixed point called the fulcrum. Levers are classified into three classes based on the relative positions of the fulcrum, load, and effort; a see-saw is a first-class lever because the fulcrum sits between the two forces. Other everyday levers include scissors, crowbars, and bottle openers. Archimedes famously claimed that with a long enough lever and a place to stand, he could move the Earth.

A screw is essentially an inclined plane wrapped helically around a cylinder, converting rotational force into linear motion or clamping force along its length. This design allows screws to hold materials together with far more force than a simple nail, since turning the screw multiplies the effort applied over many rotations. The same wrapped-inclined-plane principle appears in spiral staircases and in mechanisms like augers and drill bits. Screws are one of the six classical simple machines, alongside the lever, pulley, wheel and axle, wedge, and inclined plane.

A wedge functions as two inclined planes joined back to back, tapering to a thin edge that converts a downward or forward force into sideways splitting forces. Axes, knives, doorstops, and nails all use the wedge principle to concentrate force into a small area, making cutting or splitting easier than with a blunt tool. The longer and thinner the wedge, the greater its mechanical advantage, though it requires more distance of travel to do the same work. Like the screw, the wedge is a variation on the inclined plane, one of the six simple machines.