General Science Mixed Quiz: Set 50

The correct answer is B, Coulomb’s Law. Coulomb’s law gives the force between two point charges at rest. It states that the force is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them, and acts along the line joining them. Charles-Augustin de Coulomb established it in 1785 with a torsion balance. In free space the constant of proportionality is about 9 into 10 raised to 9 newton metre squared per coulomb squared, and the force is repulsive for like charges and attractive for unlike charges. A is wrong because Lenz’s law gives the direction of an induced current, which opposes the change in flux. C is wrong because Gauss’ law relates the electric flux through a closed surface to the charge inside it. D is wrong because Ohm’s law connects voltage, current and resistance in a conductor. Exam tip: remember the shape - Coulomb’s law is an inverse square law, like Newton’s law of gravitation.

The correct answer is C, Thallophyta. Litmus is a purple dye taken from lichens, and in the classification used in school science lichens are placed in Thallophyta, the group of simple plants whose body is an undifferentiated thallus with no true root, stem or leaf. Algae and fungi belong to the same group, and a lichen is in fact a partnership of an alga and a fungus living together. Litmus is a natural indicator: it stays purple in a neutral solution, turns red in acid and blue in base, and is used both as a solution and as litmus paper. Option A is wrong because gymnosperms are well developed plants with naked seeds, such as pine and cycas. Option B is wrong because pteridophytes, the ferns, are the first plants with vascular tissue. Option D is wrong because bryophytes such as moss and Marchantia are called the amphibians of the plant kingdom. Exam tip: litmus is red in acid, blue in base and purple when neutral.

The correct answer is C, +7. Potassium permanganate is a neutral compound, so the oxidation numbers of all its atoms must add up to zero. Potassium, an alkali metal, is always +1, and each of the four oxygen atoms is -2, giving the oxygens a total of -8. Writing the balance as 1 plus x minus 8 equals 0 gives x as +7, so manganese is in the +7 state. This is the highest oxidation state manganese can reach, because it has seven electrons available in its 3d and 4s shells, and it is why KMnO4 is such a strong oxidising agent, used to disinfect water and to titrate in the laboratory. Option A is wrong because +2 is the state of manganese in MnCl2 or MnSO4. Option B is wrong because manganese is a metal and does not take a negative state in this salt. Option D is wrong because a -7 state is impossible for a transition metal here. Exam tip: in KMnO4 manganese is +7, and in K2Cr2O7 chromium is +6.

The correct answer is C. Ultraviolet light is a transverse wave, not a longitudinal one, so this statement is the wrong one. In an electromagnetic wave the electric and magnetic fields vibrate at right angles to each other and to the direction the wave travels, which is the definition of a transverse wave. Longitudinal waves need a material to squeeze and stretch, and sound is the standard example. Option A is correct because ultraviolet light sits in the electromagnetic spectrum between visible light and X-rays. Option B is correct because electromagnetic waves need no medium and cross empty space, which is how the Sun's ultraviolet rays reach the earth. Option D is correct because ultraviolet wavelengths run from about 400 nanometres down to 10 nanometres, shorter than violet light, and this higher energy is what burns skin and is absorbed by the ozone layer. Exam tip: all electromagnetic waves are transverse; only mechanical waves such as sound can be longitudinal.

The correct answer is B, the cerebellum, which lies below and behind the cerebrum and coordinates the work of the muscles so that movement is smooth and the body stays balanced; this is why a person whose cerebellum is affected by alcohol staggers. Option A is wrong because the cerebrum, the largest part of the brain, is the seat of thought, memory, intelligence and the will to move, but not of the fine coordination that follows the order. Option C is wrong because the medulla oblongata governs the involuntary actions that keep a body alive, the heartbeat, breathing, blood pressure, vomiting, sneezing and coughing. Option D is wrong because the thalamus is a relay station that sorts sensory impulses and passes them on to the cerebrum. Keep the trio apart: cerebrum for thinking, cerebellum for balance and medulla for the involuntary.

The correct answer is C, Avogadro. The statement in the question is Avogadro's law, given by the Italian scientist Amedeo Avogadro in 1811. It says that equal volumes of all gases at the same temperature and pressure hold the same number of molecules, so the volume of a gas is directly proportional to the number of moles in it. This is why one mole of any gas occupies 22.4 litres at standard temperature and pressure, and why the number of particles in one mole, about 6.022 x 10 to the power 23, is named the Avogadro number after him. A is wrong because Charles law links the volume of a fixed mass of gas to its temperature at constant pressure. B is wrong because Boyle's law says that volume varies inversely with pressure at constant temperature. D is wrong because Gay-Lussac gave the law of combining volumes and the pressure-temperature law. Exam tip: Avogadro ties volume to the number of molecules, Boyle to pressure and Charles to temperature.

The correct answer is A, thiamine. Thiamine is vitamin B1, and its shortage causes beriberi, in which the nerves and the heart are affected, giving weakness, loss of sensation in the legs and in the wet form swelling and heart failure; the disease was common where polished rice was the staple, since polishing removes the thiamine-rich outer layer. Option B is wrong because a shortage of riboflavin, vitamin B2, gives cracks at the corners of the mouth and inflammation of the tongue. Option C is wrong because a shortage of niacin, vitamin B3, gives pellagra. Option D is wrong because ascorbic acid is vitamin C, whose deficiency gives scurvy, a disease of the gums and connective tissue. Whole grain, pulses, nuts and yeast are the usual dietary sources of thiamine.

The correct answer is C, Stomata. Stomata are the tiny pores on the surface of a leaf through which a plant takes in carbon dioxide and gives out oxygen and water vapour, so the exchange of gases takes place through them. Each stoma is bounded by two bean-shaped guard cells that swell to open the pore and shrink to close it, and this is how the plant controls its water loss. Most stomata lie on the lower surface of a leaf, so less water is lost to direct sunlight. Transpiration also happens largely through these pores. A is wrong because the cell membrane controls what enters and leaves a single cell, not the gas exchange of the whole plant. B is wrong because the nucleus carries the genetic material and directs the activities of the cell. D is wrong because guard cells only open and close the pore, while the exchange itself happens through the stomatal opening. Exam tip: stomata do the gas exchange and transpiration, guard cells only open and close them.

The correct answer is D, filament, hook and basal body. A bacterial flagellum is built of exactly these three parts.

The filament is the long thread outside the cell, made of the protein flagellin coiled into a hollow helix, and it acts like a propeller. The hook is a short curved piece that joins the filament to the cell surface and works like a universal joint. The basal body is embedded in the cell wall and the membrane, and it carries the rings and the motor that spin the filament, driven by the flow of protons across the membrane. Because of this motor the bacterial flagellum rotates, unlike the flagellum of a eukaryotic cell, which bends and whips.

A is wrong: head, tail and lower body name no part of a flagellum. B is wrong: a flagellum has no tail, and this option drops the basal body. C is wrong: it again invents a tail and leaves out the hook.

Exam tip: filament plus hook plus basal body, and the basal body is the rotary motor.

The correct answer is C, a mechanism to reduce CO2 emission. A nuclear reactor splits heavy atoms; it burns no fuel, so it releases no carbon dioxide and needs no equipment to cut such emissions. The heat of fission is produced in the reactor core, carried away by a coolant, passed to water in a heat exchanger or steam generator, and the steam then turns a turbine coupled to a generator. Control rods of cadmium or boron absorb spare neutrons and a moderator such as heavy water slows them down so that fission continues steadily. Option A is wrong as a choice because the turbine is the part that actually converts steam energy into electricity. Option B is wrong because the heat exchanger carries heat from the radioactive coolant loop to the clean water loop. Option D is wrong because the reaction chamber, the core holding the fuel rods, is where fission happens. Exam tip: a nuclear plant emits no carbon dioxide; its waste problem is spent radioactive fuel instead.

The correct answer is B, Galileo Galilei. Galileo was the first to argue that, with air resistance removed, every body falls with the same acceleration regardless of its mass. He reached this by rolling balls down inclined planes and timing them, and the idea is linked in popular accounts with his experiment from the Leaning Tower of Pisa. This overturned the older belief of Aristotle that heavier bodies fall faster. The acceleration he described is g, about 9.8 metres per second squared near the earth. A is wrong because Einstein built on this in the general theory of relativity through the equivalence principle, long afterwards. C is wrong because Edison was an inventor of the electric lamp and phonograph and did no work on falling bodies. D is wrong because Newton, born the year Galileo died, later explained why this happens through his law of gravitation. Exam tip: remember the order - Galileo found that all bodies fall alike, Newton explained the cause.

The correct answer is B, are long chain molecules held together by secondary bonds. In a thermoplastic the polymer exists as long linear or lightly branched chains, and one chain is held to the next only by weak secondary forces such as van der Waals attraction. Heat gives enough energy to loosen those weak links, so the material softens, can be moulded into a new shape and hardens again on cooling, and the cycle can be repeated, which is why thermoplastic waste is recyclable. Polyethylene, polypropylene, PVC, polystyrene and nylon all belong to this group. A is wrong because a three-dimensional network of strong primary bonds describes a thermosetting plastic such as bakelite, which sets once and cannot be remoulded. C is wrong because the ability to deform plastically rises with temperature instead of falling. D is wrong because the secondary bonds do break as thermal energy rises, and that is exactly why the plastic softens. Exam tip: thermoplastic means weak secondary bonds and remoulding, thermosetting means cross-linked primary bonds and a shape set for good.

The correct answer is D, Ar and N2. An ordinary filament bulb is filled with a mixture of argon and nitrogen because both are chemically unreactive and will not burn the white-hot tungsten filament. The filament works at about 2,500 degrees Celsius, and in air it would oxidise within seconds. The inert filling also raises the pressure inside the glass, which slows the evaporation of tungsten atoms, so the filament lasts longer and the glass blackens less. Argon is preferred among the noble gases because it is the cheapest, making up nearly one per cent of air. A is wrong because hydrogen is highly inflammable and would be a danger inside a hot bulb. B is wrong for the same reason, as the hydrogen in it makes the mixture unsafe. C is wrong because the oxygen in it would oxidise and break the filament at once. Exam tip: tungsten filament, melting point about 3,400 degrees Celsius, in an argon-nitrogen filling.

The correct answer is D, Neon. When electricity is passed through a sealed tube holding neon at low pressure, the gas atoms are excited and give out a bright orange-red glow, which is why advertising signs are still called neon signs. Neon is a noble gas discovered in 1898 by Ramsay and Travers; it is chemically inert, forms no ordinary compounds, and is also used in voltage testers, high-voltage indicators and lightning arresters. Every gas glows in its own colour in a discharge tube, and that colour is the fingerprint of its atomic energy levels. Option A is wrong because helium gives a pale pinkish-white glow and is better known for filling balloons and airships. Option B is wrong because argon glows a pale violet-blue and is used to fill electric bulbs and to shield welding. Option C is wrong because nitrogen glows bluish, and its common uses are as an inert packing gas and as a liquid coolant. Exam tip: neon gives red light in a discharge tube, while argon is the gas that fills ordinary electric bulbs.

The correct answer is C, double. Pliers and scissors are each made of two arms joined at one rivet, and each arm is a complete class 1 lever, so the tool is called a double lever. In a class 1 lever the fulcrum lies between the effort and the load; here the rivet is the fulcrum, the hand on the handle gives the effort and the jaw or blade holds the load. Because two such levers press from opposite sides, the squeeze of one hand acts on both faces of the object at once. A is wrong because there are two arms in the tool, not three. B is wrong because a single lever describes a tool with one arm, such as a crowbar or a see-saw. D is wrong because simple names the whole family of six simple machines and does not say how many levers a tool has. Exam tip: scissors, pliers and pincers are double class 1 levers, while a nutcracker is a double class 2 lever.

The correct answer is A, Capra aegagrus hircus. The domestic goat is treated as a subspecies of the wild goat, so its name carries three parts — the genus Capra, the species aegagrus and the subspecies hircus. It is often shortened to Capra hircus. Carl Linnaeus gave science this binomial system, in which the genus name begins with a capital letter, the species name does not, and the whole name is printed in italics or underlined when handwritten. Goats were among the first animals humans tamed, in western Asia roughly ten thousand years ago, and India keeps one of the largest goat populations in the world. Option B is wrong because Bos indicus is the humped Indian cattle, the zebu. Option C is wrong because Sus scrofa is the wild boar, the ancestor of the domestic pig. Option D is wrong because Ovis aries is the domestic sheep, the animal most often confused with the goat in such questions. Exam tip: goat Capra hircus, sheep Ovis aries, cattle Bos indicus, buffalo Bubalus bubalis.

The correct answer is C, Ear. Balance is controlled by the inner ear, which holds the vestibular apparatus alongside the organ of hearing. It is made of three semicircular canals set at right angles to one another and two small sacs, the utricle and the saccule. The canals are filled with fluid; when the head turns, the fluid lags behind and bends tiny hair cells, which send the brain a signal about the direction and the speed of the movement. The utricle and the saccule report the pull of gravity and straight-line motion. This is why an inner-ear infection, or spinning round quickly, leaves a person giddy. Option A is wrong because the heart only pumps blood through the body. Option B is wrong because the liver makes bile, breaks down toxins and stores glycogen. Option D is wrong because the tongue carries the taste buds and helps in speech and swallowing. Exam tip: the cochlea of the inner ear is for hearing, and the three semicircular canals are for balance.

The correct answer is C, Cleaning. In electroplating the article to be coated is made the cathode, the plating metal serves as the anode, and both are dipped in an electrolyte containing a salt of that metal. When current flows, the metal ions travel to the cathode and settle on it. The coating can bond only if the surface is chemically clean, so grease, oil, rust and oxide are stripped off first by degreasing and by pickling in acid; any film left behind makes the plating peel, blister or come out patchy. Option A is wrong because buffing only brings up a shine on a surface that is already clean. Option B is wrong because soldering joins two metals with a filler alloy and has nothing to do with preparing a surface for plating. Option D is wrong because polishing smooths the surface mechanically but does not remove the oily and oxide films that spoil adhesion. Exam tip: the order is clean first, then plate, and the article is always the cathode.

The correct answer is A, Petiole. The petiole is the stalk that joins a leaf blade to the stem; it belongs to the leaf, not to the flower, and a leaf without one is called sessile. A typical flower is built of four whorls borne on the thalamus. The calyx is the outermost ring of sepals, which protect the bud. Inside it the corolla of petals attracts pollinators. Then comes the androecium, the male whorl, whose units are the stamens, each with an anther on a filament. At the centre is the gynoecium, the female whorl, whose unit is the pistil or carpel, made of stigma, style and ovary. Option B is wrong because the pistil is the female part of the flower. Option C is wrong because the stamen is its male part. Option D is wrong because sepals form the calyx, the flower's outermost whorl. Exam tip: the four floral whorls are calyx, corolla, androecium and gynoecium; the petiole is a part of the leaf.

The correct answer is A, Two dry surfaces. Coulomb friction, also called dry friction, is the resistance that acts when two solid surfaces touch each other with no lubricant between them. Charles-Augustin de Coulomb set out its rules: the friction force is proportional to the normal reaction, it does not depend on the apparent area of contact, and it is very nearly independent of the sliding speed. Dry friction covers both the static friction that must be beaten before motion can start and the kinetic friction that acts once sliding has begun, and the limiting static value is the larger of the two. Option B is wrong because friction between lubricated surfaces is called fluid or film friction and obeys the laws of viscosity instead. Option C is wrong because relative motion describes kinetic friction, which is only one part of Coulomb friction. Option D is wrong because the resistance between a solid and a liquid is viscous drag. Exam tip: Coulomb friction means dry friction, proportional to the normal reaction and independent of the contact area.