General Science MCQs – Page 19 (Q181-190)

A periscope commonly uses two plane mirrors, or right-angle prisms in more advanced designs, angled at 45 degrees and positioned parallel to each other inside a tube, allowing a person to see over or around obstacles by reflecting light down through the device via two successive reflections. This simple application of the law of reflection was historically vital in submarines, allowing crews to observe the surface while remaining submerged, and in tanks and trenches for observing surroundings while staying under cover. Modern periscopes often use prisms rather than mirrors since prisms suffer less from silvering degradation and light loss over repeated use.

A kaleidoscope creates colorful repeating patterns mainly through the use of multiple mirrors, typically two or three arranged at specific angles inside a tube, which repeatedly reflect a small collection of loose, colored objects like beads or glass fragments at one end. Each reflection produces additional mirrored copies of the original pattern, and because the objects are free to move, gently rotating the kaleidoscope shifts their arrangement, creating a constantly changing, symmetrical pattern. The word kaleidoscope derives from Greek words meaning beautiful form watcher, and the device was patented by Scottish physicist David Brewster in 1817 while researching light polarization.

Thunder is generally heard a few seconds after lightning is seen mainly because light travels far faster than sound, roughly a million times faster, meaning the flash of lightning reaches an observer's eyes almost instantaneously while the accompanying thunder, generated by the same event, takes measurably longer to arrive. This time delay can be used to estimate the distance to a lightning strike, since sound travels at roughly 343 meters per second, meaning a delay of about three seconds corresponds to a distance of roughly one kilometer. Both the flash and the sound originate simultaneously from the same rapid heating and expansion of air along the lightning channel.

The SI unit used to measure the strength of an electric current is the ampere, commonly shortened to amp, named after French physicist Andre-Marie Ampere, a founding figure in the study of electromagnetism. One ampere corresponds to a flow of one coulomb of electric charge, or about 6.24 quintillion electrons, passing a given point every second. Current is distinct from voltage, measured in volts, and resistance, measured in ohms, though the three are directly related through Ohm's law, and household appliances and circuit breakers are commonly rated in amperes to indicate how much current they draw or can safely handle.

The volt is the SI unit used to measure electric potential difference, commonly called voltage, named after Italian physicist Alessandro Volta, who invented the first chemical battery in 1800. Voltage represents the amount of energy, in joules, available to move each coulomb of electric charge through a circuit, effectively acting as the electrical pressure that drives current through a conductor. It should not be confused with the ampere, which measures the rate of charge flow, or the ohm, which measures resistance to that flow, though all three quantities are linked together through the fundamental relationship described by Ohm's law.

A short circuit occurs when electric current takes an unintended path of very low resistance, often bypassing the normal circuit components such as a lamp or appliance, which causes an abnormally large surge of current to flow, since a lower resistance allows much more current for the same voltage according to Ohm's law. This sudden surge generates excessive heat rapidly, which can melt wire insulation, damage components, or start an electrical fire, making short circuits a leading cause of household electrical hazards. Fuses and circuit breakers are specifically designed to detect this dangerous current surge and quickly interrupt the circuit before serious damage or fire occurs.

Electrical insulation around wires is mainly intended to prevent accidental electric shock, by using materials with extremely high resistance, such as rubber or PVC plastic, to keep dangerous current confined safely within the conductor rather than allowing it to flow into anyone or anything that touches the wire. Insulation also prevents short circuits by keeping adjacent live wires from directly contacting each other or a grounded surface. Damaged, cracked, or aged insulation is a significant safety hazard, which is why electrical codes require regular inspection and replacement of worn wiring, particularly in older buildings and humid environments where insulation can degrade faster.

An earthing, or grounding, wire in household wiring mainly provides a safe path for excess or fault current, such as current that accidentally leaks onto the metal casing of an appliance due to internal insulation failure, directing it safely into the earth rather than through a person who touches the appliance. This significantly reduces the risk of severe electric shock, since electricity naturally follows the path of least resistance, and a properly grounded system offers a much lower-resistance path to earth than through a human body. Grounding also helps protect sensitive electronic equipment from voltage spikes and is a mandatory safety feature in modern electrical codes worldwide.

A fluorescent tube light produces visible light mainly using mercury vapor, which emits ultraviolet radiation when electrically excited by an internal electric discharge, combined with a phosphor coating lining the inside of the glass tube, which absorbs this invisible ultraviolet light and re-emits it as visible light through a process called fluorescence. This two-step process makes fluorescent lighting significantly more energy-efficient than traditional incandescent bulbs, since less energy is wasted as heat. Different phosphor blends can be used to adjust the color temperature of the emitted light, ranging from warm yellowish-white to cool bluish-white lighting.

A traditional incandescent light bulb produces light by heating a thin filament, commonly made of tungsten due to its extremely high melting point of about 3,422 degrees Celsius, until it glows white-hot, a process called incandescence. Tungsten was chosen because it can withstand the intense heat generated by the electric current passing through it without melting or breaking too quickly, though the filament still gradually thins and eventually fails over time. Incandescent bulbs are highly inefficient, converting only about 5 percent of their energy into visible light and wasting the rest as heat, which is why more efficient LED and fluorescent lighting have largely replaced them.