General Science Mixed Quiz: Set 62

The correct answer is B, The force of gravitation is doubled. Gravitational force is directly proportional to each mass, so doubling one mass doubles the force.

Newton law of universal gravitation states that the force between two bodies is F equal to G m1 m2 divided by r squared. Here G is the universal gravitational constant, about 6.67 into 10 to the power minus 11 newton metre squared per kilogram squared, and r is the distance between the centres. If m1 is doubled and nothing else changes, the numerator doubles and so does F.

Option A would be right only if both masses were doubled, or if the distance were halved. Option C does not follow from the formula. Option D is the opposite of what happens; the force would halve if one mass were halved. Note that the force depends on the square of the distance, so doubling r makes the force one fourth.

Exam tip: force is proportional to m1 into m2 and inversely proportional to r squared.

The correct answer is A, 1 and 4. Hooke's law holds only as far as the limit of proportionality, and that limit is either equal to or lower than the elastic limit, so statements 1 and 4 are the correct pair. Hooke's law says stress is proportional to strain, which is the straight part of the stress-strain graph; the point where the curve leaves the straight line is the limit of proportionality. A little beyond it the material still springs back to its original shape, and the last point at which it does so is the elastic limit. For most metals the two points lie very close together and for an ideal material they coincide. B is wrong because statement 2 extends the law past the straight part of the graph, where stress and strain are no longer proportional. C and D are wrong because statement 3 says always less, while the two limits may also be equal. Exam tip: order the four points as proportionality limit, elastic limit, yield point, ultimate stress.

The correct answer is B, The f-block. Atomic number 59 is praseodymium, a lanthanide, and the lanthanides and actinides together make up the f-block.

A block is named after the sub-shell that the last electron enters. Praseodymium has the configuration of xenon followed by 4f3 and 6s2, so the differentiating electron goes into the 4f sub-shell. The f-block runs from atomic number 58 to 71, the lanthanides, and from 90 to 103, the actinides; these two rows are printed separately below the main table and are called the inner transition elements.

Option A is wrong because the s-block is groups 1 and 2, the alkali and alkaline earth metals. Option C is wrong because the p-block is groups 13 to 18. Option D is wrong because the d-block is groups 3 to 12, the transition metals, where the last electron enters a d sub-shell.

Exam tip: 58 to 71 are lanthanides and 90 to 103 are actinides, both in the f-block.

The correct answer is C, fish farming. Pisciculture is the rearing of fish in ponds, tanks and other managed waters, the Latin word piscis meaning fish. It is a branch of aquaculture and India is one of the largest fish producers in the world; the Blue Revolution is the name given to the planned growth of fish output, and rohu, catla and mrigal are the common Indian carps raised in ponds. A is wrong because the rearing of honey bees is apiculture, which gives honey and beeswax. B is wrong because the rearing of silkworms is sericulture, in which the mulberry-fed Bombyx mori gives most of the world's silk. D is wrong because the rearing of birds is aviculture, and the keeping of fowl for eggs and meat is poultry farming. Exam tip: learn the culture words together - pisciculture fish, apiculture bees, sericulture silkworms, aviculture birds, horticulture fruits and vegetables, floriculture flowers.

The correct answer is B, Aluminium. Aluminium is the most abundant metal in the crust of the earth, making up about eight per cent of it by weight.

Among all elements of the crust, oxygen comes first and silicon second, and aluminium is third, which makes it the first among metals. It never occurs free in nature because it is highly reactive; its chief ore is bauxite, from which the metal is extracted by electrolysis of molten alumina in the Hall-Heroult process. Aluminium is light, resists corrosion because of a thin oxide film, and is used in aircraft, wires, utensils and foil.

Option A, sodium, is far less abundant and is found in common salt and feldspars. Option C, calcium, follows aluminium and iron, and occurs in limestone and gypsum. Option D, iron, is the second most abundant metal in the crust, though it is the most abundant element in the earth as a whole, counting the core.

Exam tip: in the crust, oxygen, silicon, aluminium, iron; so aluminium is the first metal, iron the second.

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 C, eukaryotic cells. A cell whose nucleus is well organised and bounded by a nuclear membrane is called a eukaryotic cell.

The word comes from the Greek eu, meaning true, and karyon, meaning kernel or nucleus. Besides a true nucleus, eukaryotic cells have membrane-bound organelles such as mitochondria, the endoplasmic reticulum and the Golgi apparatus, and their DNA is organised into several linear chromosomes. All animals, plants, fungi and protists are made of such cells.

Option A, cheek cells, names one particular human epithelial cell used in school slides; it is an example of a eukaryotic cell, not the class itself. Option B, autokaryotic cells, is not a term used in biology. Option D, prokaryotic cells, are the opposite case: bacteria and archaea have no nuclear membrane, so their genetic material lies free in the cytoplasm in a region called the nucleoid.

Exam tip: eukaryote means true nucleus with a membrane; prokaryote means no nuclear membrane.

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 B, Purity of gold in the king crown. Archimedes used his principle to test whether the crown of King Hiero II of Syracuse was pure gold.

The principle says that a body immersed in a fluid is buoyed up by a force equal to the weight of the fluid it displaces. Because gold is denser than silver, a crown of the same weight mixed with silver would be bulkier and would displace more water. By comparing the water displaced by the crown with that displaced by an equal weight of pure gold, Archimedes could show the crown had been adulterated. The story of him crying out eureka in his bath comes from this episode.

Option A is wrong because milk purity is tested with a lactometer, a later instrument that works on density. Options C and D are wrong because ships and submarines apply the law of flotation, but they were not what Archimedes was asked to test.

Exam tip: Archimedes principle, buoyant force equals weight of displaced fluid, used on the gold crown.

The correct answer is A, Wild yak. Bos mutus is the scientific name of the wild yak, the long haired bovine of the high cold plateaus of Ladakh, Tibet and the Karakoram, which grazes above four thousand metres and is listed as Vulnerable on the IUCN Red List. The domestic yak is called Bos grunniens, the grunting ox, and mutus means mute, since the wild animal is far quieter. The two part naming system, with the genus first and the species second, was given by Carl Linnaeus. B is wrong because the horse is Equus caballus. C is wrong because the ox, meaning domestic cattle, is Bos taurus or Bos indicus for the humped Indian breeds. D is wrong because the Asiatic water buffalo is Bubalus bubalis. Exam tip: the genus Bos covers cattle and yak, Bos mutus wild yak and Bos grunniens domestic yak.

The correct answer is C, carbon-14. Carbon-14 is the radioactive isotope of carbon used for radiocarbon dating, and its half-life is close to 5,700 years, which is the figure quoted in the question. A living plant or animal takes in carbon-14 with ordinary carbon; after death the intake stops and the carbon-14 decays by beta emission, so the proportion remaining in wood, bone, cloth or parchment gives the age of the specimen. Option A is wrong because carbon-9 is a very short-lived isotope of no use in dating. Option B is wrong because carbon-12 is the ordinary stable isotope of carbon and is the standard for atomic masses, so it does not decay at all. Option D is wrong because carbon-17 is an extremely unstable isotope that survives only for a fraction of a second.

The correct answer is D, Ligament. A ligament is the connective tissue that joins one bone to another at a joint. It is very elastic and strong, and it holds the bones in place so that a joint can move without the bones slipping apart. Ligaments contain little matrix of their own and are stretched when a joint is twisted, which is what happens in a sprain. A is wrong because a tendon joins a muscle to a bone; tendons are fibrous and strong but have limited stretch, so the pull of a muscle is passed straight to the bone. B is wrong because cartilage is the smooth, flexible tissue that pads the ends of bones and shapes the nose and ear, cushioning the joint rather than tying the bones together. C is wrong because matrix is the material in which the cells of a connective tissue are embedded, not a structure by itself. Exam tip: ligament bone to bone, tendon muscle to bone.

The correct answer is B, decreases. A semiconductor has a small forbidden energy gap, so heating supplies thermal energy that pushes more electrons from the valence band into the conduction band, creating more electron-hole pairs. More charge carriers mean higher conductivity, and therefore lower resistance, which is why a semiconductor is said to have a negative temperature coefficient of resistance. Option A is wrong because resistance rises with temperature in metals, where the carriers are already free and increased lattice vibration merely obstructs them; students apply the metallic rule here by mistake. Option C is wrong because the resistance change in a semiconductor is in fact large and is used in thermistors. Option D is wrong because the resistance never becomes zero; it falls steadily but a semiconductor does not become a superconductor on heating.

The correct answer is B, Fallopian tube. In human beings the sperm meets and fuses with the egg inside the fallopian tube, also called the oviduct.

The ovary releases one egg in a month, and the funnel shaped mouth of the fallopian tube collects it. Sperms swim up from the vagina through the cervix and the uterus into the tube, and fusion usually happens in its wider upper part. The fertilised egg, now a zygote, begins to divide as the tube's lining pushes it along, and reaches the uterus in a few days as a ball of cells that implants in the thick uterine wall and grows there with the help of the placenta.

Option A is wrong because the uterus is where the embryo implants and develops, after fertilisation. Option C is wrong because the ovary only makes and releases the egg. Option D is wrong because the vagina is the passage the sperms enter through.

Exam tip: egg made in the ovary, fertilised in the fallopian tube, developed in the uterus.

The correct answer is B, Concrete. Concrete is the building material made by mixing cement with coarse aggregate such as gravel, fine aggregate such as sand, and water.

The cement and water react in a process called hydration, which sets into a hard mass and binds the aggregate together. A common ratio for ordinary work is one part cement, two parts sand and four parts gravel, written as 1:2:4. Concrete is strong in compression but weak in tension, so steel bars are embedded in it to make reinforced cement concrete, the material of most modern buildings, bridges and dams.

Option A, mortar, is cement or lime with sand and water only, with no coarse aggregate, and is used to join bricks. Option C, slurry, is any thin, pourable mix of a solid in a liquid. Option D, a moderator, is the material that slows neutrons in a nuclear reactor.

Exam tip: mortar has no gravel; concrete has gravel; adding steel gives RCC.

The correct answer is C, Hepatitis B. The hepatitis B vaccine was the first vaccine made by recombinant DNA technology. Scientists cut out the gene for the surface protein of the hepatitis B virus and put it into yeast cells; the yeast then made that protein in large amounts, and the purified protein is injected as the vaccine. Because only one viral protein is used and no whole virus is involved, the vaccine cannot cause the disease, which is what makes recombinant vaccines safe. It was licensed in the mid 1980s and in India it is part of the pentavalent shot given to infants. A is wrong because the polio vaccine is either the killed virus of Salk or the weakened live virus of Sabin. B is wrong because no vaccine against AIDS has been licensed so far. D is wrong because the smallpox vaccine used the live vaccinia virus, and the disease was declared eradicated in 1980. Exam tip: hepatitis B, first recombinant vaccine, made in yeast from the surface antigen gene.

The correct answer is A, nuclear fission and nuclear fusion. A hydrogen bomb, also called a thermonuclear bomb, works in two steps. A fission explosion of uranium or plutonium produces the temperature of millions of degrees needed to force light nuclei together, and the fusion of those nuclei then releases far more energy than the fission stage alone. So both processes contribute to the explosion. Option B is wrong because fission alone describes the atom bomb of the earlier type, which is less powerful. Option C is wrong because cryogenic hydrogen, that is hydrogen liquefied at very low temperature, is rocket fuel and has nothing to do with the bomb's energy. Option D is wrong because merely compressing hydrogen releases no nuclear energy; the nuclei must be made to fuse.

The correct answer is C, arsenic. An n-type semiconductor is made by doping with a pentavalent element, that is one with five valence electrons, such as phosphorus, arsenic, antimony or bismuth. Four of the five electrons form covalent bonds with neighbouring silicon atoms and the fifth is left almost free, so the impurity acts as a donor and electrons become the majority carriers. Option A is wrong because boron is trivalent and gives p-type material. Option B is wrong because indium is also trivalent and is a classic acceptor impurity. Option D is wrong for the same reason, as gallium has three valence electrons. The memory aid is that pentavalent means donor and n-type, while trivalent means acceptor and p-type, and the doped crystal stays electrically neutral in both cases.

The correct answer is A, Henri Becquerel. In 1896 Becquerel found that a uranium salt kept in the dark fogged a wrapped photographic plate, which showed that the salt emitted its own penetrating radiation without being exposed to light. Option B is wrong, although Marie Curie, with her husband Pierre, discovered polonium and radium in 1898, coined the word radioactivity and shared the Nobel Prize with Becquerel; the discovery of the effect itself is his. Option C is wrong because Rutherford came later and separated the emissions into alpha, beta and gamma rays, proposed the nuclear model of the atom and achieved the first artificial transmutation. Option D is wrong because Roentgen discovered X-rays in 1895, which are produced outside the nucleus and are not a form of radioactivity.

The correct answer is B, holes. A p-type semiconductor is made by adding a trivalent impurity such as boron, aluminium, gallium or indium. Because the impurity atom has only three valence electrons, one covalent bond is left incomplete and a vacancy called a hole is created; the impurity therefore acts as an acceptor and holes are the majority carriers, while the few thermally generated electrons are the minority carriers. Option A is wrong because electrons are the majority carriers in n-type material, not p-type. Option C is wrong because protons are bound in the nuclei and never act as charge carriers in a solid. Option D is wrong because the acceptor ions are fixed in the crystal lattice and cannot move, so they carry no current even though they are negatively charged.