General Science Mixed Quiz: Set 34

The correct answer is A, 1038 m. An echo is the sound heard when a wave is reflected from a distant obstacle and comes back, so in the time measured the sound covers the distance to the cliff and then the same distance back again. The total path is therefore twice the distance, and twice the distance equals v into t, that is 346 into 6 = 2076 metres. Dividing by two gives a distance of 1038 metres. For an echo to be heard as a separate sound the reflecting surface must be far enough away that the return takes at least 0.1 second, which in air needs a distance of about 17 metres. Option B is wrong because 1083 is only a rearrangement of the digits of the correct figure. Option C is wrong because 2076 m is the full to-and-fro path rather than the distance to the cliff. Option D is wrong because 2706 follows from neither step of the calculation. Exam tip: the distance of the reflector equals v into t divided by 2, and the minimum distance for a distinct echo in air is about 17 m.

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 A, gold. Ductility is the property of being drawn into a wire, and gold is the most ductile metal known; it is also the most malleable, so a very small quantity can be beaten into an extremely thin sheet or drawn into a very long wire. Option C, silver, is the next most ductile and is the best conductor of both heat and electricity, which is why it is easy to confuse the two superlatives; remember that silver leads in conduction while gold leads in ductility and malleability. Option B, copper, is ductile enough to be drawn into the wires used in household wiring, but far less so than gold. Option D, iron, is ductile when hot but comparatively hard and is valued for strength rather than for being drawn out.

The correct answer is A, Crown Gall. Crown gall is caused by the bacterium Agrobacterium tumefaciens, which enters through a wound near the base, or crown, of the stem and makes the plant grow rough tumour-like swellings there. The bacterium works by pushing a piece of its own Ti plasmid into the plant's cells and forcing them to divide, and that natural trick is why laboratories use it as a vector to carry new genes into plants. Grapevine, apple, rose, walnut and stone fruits suffer the most. Option B is wrong because mosaic diseases, such as tobacco mosaic, are caused by viruses that mottle the leaves in light and dark patches. Option C is wrong because smut of wheat, bajra and sugarcane is a fungal disease that fills the ear with black powdery spores. Option D is wrong because white blister, or white rust, of crucifers such as mustard is also fungal and raises white blisters on leaves and stems. Exam tip: bacterial — crown gall, citrus canker, bacterial blight of rice; viral — mosaic, leaf curl; fungal — smut, rust, blight.

The correct answer is B, dienes. The prefix di stands for two and the ending ene for a carbon to carbon double bond, so a diene is a hydrocarbon carrying exactly two such bonds; buta-1,3-diene, the raw material of synthetic rubber, is the standard example. Option A is wrong because terpenes are a class of natural compounds built from isoprene units and found in the oils of plants; they may contain several double bonds but the name says nothing about the number. Option C is wrong because the ending yne refers to a triple bond, so a name of that kind would describe three triple bonds and not double bonds at all. Option D is wrong for the same reason: it would mean two triple bonds. Reading the prefix for the count and the ending for the kind of bond answers the whole family of such questions.

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, Geitonogamy. Geitonogamy is pollination between two different flowers borne on the same plant. It is an odd halfway case: because the pollen has to travel from one flower to another it needs an agent such as an insect or the wind, so in working it looks like cross-pollination, yet the pollen comes from the same plant, so genetically it is self-pollination and brings no new variation. A is wrong because autogamy is pollination within the same flower, where pollen falls on the stigma of that very flower, as in pea and wheat. C is wrong because xenogamy is the transfer of pollen to the stigma of a flower on a different plant, and it is the only one of the three that brings genetically different pollen and so gives rise to variation. D is wrong because option B already names the process correctly. Exam tip: autogamy – same flower; geitonogamy – same plant, another flower; xenogamy – another plant.

The correct answer is A, 250 cm. In an astronomical telescope set for normal adjustment, the magnifying power equals the focal length of the objective divided by the focal length of the eyepiece. Here the magnification is 100 and the eyepiece is 2.5 cm, so the objective must be 100 multiplied by 2.5, that is 250 cm. This is why astronomical telescopes are long instruments: a large objective focal length with a short eyepiece focal length gives high magnification, and in normal adjustment the tube length is roughly the sum of the two focal lengths. B is wrong because an objective of 40 cm would give a magnification of only 16. C is wrong because a focal length smaller than the eyepiece would shrink the image instead of enlarging it. D is wrong because 100 cm gives a magnification of 40. Exam tip: for a telescope magnification is objective divided by eyepiece, so the objective is the longer lens.

The correct answer is B, Surface tension and viscosity both decrease. Heating a liquid makes its molecules move faster and sit a little further apart, so the attraction between them weakens, and both properties depend on that attraction. Surface tension arises because molecules at the surface are pulled inward by their neighbours, and that inward pull fades as temperature rises until it reaches zero at the critical temperature. Viscosity in a liquid comes from molecules gripping each other as layers slide past, so the same weakening makes the liquid thinner and easier to pour, which is why warm oil flows far more freely than cold oil. A is wrong because surface tension falls rather than rises on heating. C is wrong because neither of the two rises. D is wrong because viscosity of a liquid falls, not rises. Exam tip: liquids thin out on heating, but a gas becomes more viscous when heated.

The correct answer is A, Used on ordinary combustibles such as wood and paper. Fires are sorted into classes by what is burning, and Class A covers ordinary solid fuels — wood, paper, cloth, straw, rubber and many plastics. These fires leave glowing embers, so they are put out mainly by cooling, and plain water or a water-based extinguisher is the cheapest and most effective choice for them. Option B is wrong because burning liquids such as petrol, kerosene, oil, paint and solvents are Class B, where water would spread the fire and foam or dry powder is used instead. Option C is wrong because a fire in live electrical equipment is a separate class — Class C in the American scheme and marked Class E in the Indian and European ones — and it needs a non-conducting agent such as carbon dioxide, never water. Option D is wrong because burning metals such as magnesium, sodium and potassium form Class D and need a special dry powder, since water reacts violently with them. Exam tip: A — solids, B — liquids, C — gases, D — metals, F or K — cooking oil.

The correct answer is C, Red color scatters less than other colors. At sunset the Sun is close to the horizon, so its light travels through a much thicker layer of atmosphere before it reaches the eye. Air molecules scatter short wavelengths, blue and violet, far more strongly than long ones; this is Rayleigh scattering, in which the scattering falls off as the fourth power of the wavelength. Over that long slanting path almost all the blue is scattered sideways out of the beam, and mostly the long-wavelength red and orange light survives to reach us, so the Sun and the sky around it look red. Option A is wrong because sunlight is white and contains all seven colours. Option B is wrong because red is scattered the least, not the most; blue is scattered most, which is why the midday sky is blue. Option D is wrong because the effect lies in the atmosphere, not in the sensitivity of the eye. Exam tip: Rayleigh scattering gives a blue sky at noon and a red Sun at sunrise and sunset.

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 C, Germanium. Germanium is not used to build light emitting diodes because it is an indirect band gap semiconductor, so an electron falling back across the gap gives up most of its energy as heat in the crystal rather than as light. Its band gap is also very small, about 0.66 electron volt, which is far too little to produce visible light. Light emitting diodes are therefore made from direct band gap compounds, whose gap can be tuned to the colour wanted. A is wrong because gallium phosphide is used for green and yellow diodes. B is wrong because indium gallium nitride gives the blue and white diodes that made modern lighting possible and won the Nobel Prize in Physics in 2014. D is wrong because gallium arsenide is the standard material for red and infrared diodes, including the ones inside television remote controls. Exam tip: light emitting diodes need direct band gap materials such as gallium arsenide, gallium phosphide and indium gallium nitride; silicon and germanium are indirect and do not emit light.

The correct answer is C, 18% Tungsten. High-speed steel is named 18-4-1 after the three metals added to it in that order: 18 per cent tungsten, 4 per cent chromium and 1 per cent vanadium, with iron making up the rest along with a little carbon. Tungsten is the heart of the alloy because it keeps the steel hard even when the cutting edge glows red hot, so drills, milling cutters and lathe tools made from it can cut at high speed without losing their edge. Chromium adds hardness and resistance to rust, and vanadium refines the grain and improves wear resistance. A is wrong because chromium in this grade is 4 per cent, not 1. B is wrong because the 18-4-1 grade has no nickel; nickel goes into stainless steel and into invar. D is wrong because vanadium is the 1 per cent part of the name. Exam tip: 18-4-1 means tungsten 18, chromium 4, vanadium 1.

The correct answer is C, Yeast, amoeba, bacteria. All three are unicellular, which means a single cell carries out every job of life. In a unicellular organism that one cell manages nutrition, respiration, movement and reproduction, while a multicellular body shares the work among tissues and organs. Yeast is a single-celled fungus used in baking and brewing, amoeba is a single-celled protozoan that moves and feeds with pseudopodia, and bacteria are single-celled organisms whose cells have no true nucleus. A is wrong because hydra, though a simple animal, is multicellular, with a body wall and tentacles made of many cells. B is wrong for the same reason, as sea anemone is a multicellular animal of the phylum Cnidaria, even though paramecium and bacteria are single-celled. D is wrong because only paramecium in that group is unicellular; hydra and sea anemone are both multicellular. Exam tip: unicellular – bacteria, amoeba, paramecium, yeast, chlamydomonas; multicellular – hydra, sea anemone, spirogyra.

The correct answer is C, water bodies. Red algae, the division Rhodophyta, live in water, mostly in warm and shallow sea water, with a few species in fresh water. Their colour comes from the pigment phycoerythrin, which masks the green of chlorophyll and lets them use the blue light that reaches greater depths, so some grow deeper than other algae. Porphyra, Gracilaria and Polysiphonia are common examples, and the agar used in laboratories and the carrageenan used in food both come from this group. Coralline red algae deposit calcium carbonate and help build coral reefs. Option A is wrong because bare mountain slopes lack the standing water algae need. Option B is wrong because a city is a settlement, not a water body or habitat for marine algae. Option D is wrong because deserts are dry and an alga cannot complete its life cycle without water. Exam tip: Rhodophyta are red from phycoerythrin, Chlorophyta green from chlorophyll, Phaeophyta brown from fucoxanthin.

The correct answer is A, hammer, anvil and stirrup. The middle ear holds three tiny bones, the smallest in the human body, called the malleus, the incus and the stapes, which in everyday English are the hammer, the anvil and the stirrup. Sound waves collected by the pinna travel down the ear canal and set the eardrum vibrating. The three ossicles pass that vibration along in a chain and amplify it about twenty times before handing it to the oval window of the cochlea, where the fluid inside converts it into nerve signals for the auditory nerve. The stapes is the smallest bone in the body, roughly 3 mm long. Option B is wrong because the cochlea is the spiral fluid-filled part of the inner ear, not a middle-ear bone. Option C is wrong because the pinna is the outer flap of the ear. Option D is wrong because there is no bone called the auditory bone. Exam tip: malleus, incus and stapes are the hammer, anvil and stirrup, and the stapes is the smallest bone in the human body.

The correct answer is A, Papaya. A unisexual flower carries only one kind of reproductive organ, either stamens or a pistil, while a bisexual flower carries both. Papaya is dioecious: male and female flowers are borne on separate plants, so pollen must travel from a male tree to a female tree before fruit can set, which is why growers keep a few male trees in a papaya orchard. Other familiar unisexual examples are maize, cucumber, watermelon and coconut, in which the two kinds of flower sit on the same plant and the plant is called monoecious. Option B is wrong because the disc florets of a sunflower head are bisexual. Option C is wrong because the hibiscus flower is a standard bisexual flower carrying both stamens and a pistil. Option D is wrong because mustard, a member of the family Brassicaceae, also bears bisexual flowers. Exam tip: unisexual flowers include papaya, maize, cucumber and watermelon, while hibiscus, mustard, rose and pea are bisexual.

The correct answer is C, To increase friction. The grooves cut into a sole grip the ground, so the foot does not slip while walking or running. Friction is the force that acts between two surfaces in contact and opposes motion between them. It becomes larger when the surfaces are rough, which is why the tread of a sole, the grooves of a tyre and the ridges of a bicycle handle are all made rough on purpose. A smooth sole on a wet floor has very little friction, and that is why people slip there. The same rubbing slowly wears the tread away, so an old shoe or tyre grips poorly and has to be replaced. A is wrong because a sole protects the foot by its thickness and material, not by its pattern. B is wrong because less friction would make walking unsafe; oil and ball bearings are used where friction has to be reduced. D is wrong because treading does not lengthen the life of a shoe. Exam tip: rough surface means more friction – treads, grooves and studs are all made to grip.

The correct answer is D, copper and zinc. Brass takes the workability of copper and the hardness of zinc, resists corrosion and is easy to cast, which is why it is used for utensils, locks, taps, fittings and wind instruments. Option A, copper and tin, is bronze, and the brass and bronze pair is the single most frequently confused item in this chapter, so fix zinc with brass and tin with bronze. Option B, copper and nickel, is cupronickel, used in coins and in condenser tubes. Option C, copper and iron, is not a standard alloy of this kind, though iron and copper occur together in the ore copper pyrites. Related alloys are worth learning with these: German silver is copper, zinc and nickel; gun metal is copper, tin and zinc; and bell metal is copper with a larger proportion of tin.