General Science Mixed Quiz: Set 64

The correct answer is A, the becquerel. One becquerel is one disintegration per second, and it is the SI unit of the activity of a radioactive source, named after the discoverer of radioactivity. Option B is wrong because the curie is the older unit of activity, based on the activity of a gram of radium, and one curie equals 3.7 into ten to the power ten becquerel; it is still quoted but is not the SI unit. Option C is wrong because the gray measures absorbed dose, that is the energy deposited in a kilogram of matter, and it replaced the rad. Option D is wrong because the sievert measures equivalent dose, which weights the absorbed dose by the harm the type of radiation does to tissue, and it replaced the rem.

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, Bardeen, Brattain and Shockley. John Bardeen, Walter Brattain and William Shockley built the first working transistor at Bell Laboratories in 1947 and shared the Nobel Prize in Physics in 1956 for the discovery of the transistor effect. Option A is wrong because Jack Kilby and Robert Noyce are associated with the integrated circuit, developed from 1958, for which Kilby received the Nobel Prize in Physics in 2000. Option B is wrong because J. J. Thomson discovered the electron and Rutherford the nucleus, both long before electronics. Option D is wrong because Faraday and Maxwell belong to the nineteenth century work on electromagnetism. The word transistor itself is formed from transfer and resistor. The device they built was a point-contact transistor in germanium, and Shockley went on to describe the junction transistor that made mass production possible; the three names are usually asked together as a set.

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, Au, that is gold. Malleability is the property of being beaten into thin sheets and ductility the property of being drawn into wires, and gold possesses both to the highest degree of any metal: a single gram can be beaten into a sheet of about one square metre and drawn into a wire of great length, which is why gold leaf and gold wire have been made for centuries. Option A is wrong because sodium is so soft that it can be cut with a knife and is reactive enough to be stored under kerosene, so it cannot be drawn into a usable wire. Option C is wrong because cerium, a lanthanide used in lighter flints and alloys, is brittle and not valued for either property. Option D is wrong because mercury is the only metal that is liquid at room temperature, and a liquid can be neither beaten into sheets nor drawn into wires.

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, spontaneous. In spontaneous combustion a substance catches fire by itself, without any external flame being brought near it. This happens when the slow oxidation of the substance in air releases more heat than the substance needs to reach its own ignition temperature, so the heat accumulates until the material bursts into flame. White phosphorus is the standard laboratory example, and heaps of coal dust, oily rags and damp haystacks catch fire in the same way. A, rapid combustion, is wrong because there the fuel burns quickly only after it is ignited by an outside source, as cooking gas does when a match is brought to it. C, complete combustion, describes the quality of burning, not how it starts: it means the carbon of the fuel is fully converted to carbon dioxide because oxygen is plentiful. D, explosive combustion, is wrong because it describes a reaction so fast that gas, heat, light and sound are produced in an instant, as in a firecracker.

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 A, Tarapur in Maharashtra. The Tarapur Atomic Power Station was the first nuclear power station in India and also the first in Asia, built with American collaboration and using boiling water reactors, unlike the pressurised heavy water reactors of the later Indian stations. Option B is wrong because Kalpakkam, the Madras Atomic Power Station, came later and is known as the site of the prototype fast breeder reactor of the second stage. Option C is wrong because Rawatbhata in Rajasthan was the second station, built with Canadian collaboration. Option D is wrong because Narora in Uttar Pradesh is later still. Candidates should keep Apsara, the first research reactor at Trombay in 1956, separate from Tarapur, the first power station. Apsara was a research reactor for experiments and isotope production, while Tarapur generated electricity for the grid, and that difference is what the question turns on.

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 C, it remains electrically neutral in both cases. Doping replaces a few host atoms with impurity atoms, and each impurity atom brings its own nucleus along with its electrons, so the total positive and negative charge in the crystal stays balanced. The names n-type and p-type describe which carrier is in the majority, not an overall charge. Option A is wrong because the extra electron contributed by a donor is matched by the extra proton in the donor nucleus. Option B is wrong for the same reason on the acceptor side. Option D is wrong because doping raises conductivity sharply, often by several orders of magnitude, which is the whole purpose of the process and the reason extrinsic semiconductors, not pure ones, are used in devices.

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 B, lead. Galena is lead sulphide, with the formula PbS, and is the principal ore from which lead is extracted; being a sulphide, it is concentrated by froth flotation and then roasted to the oxide before reduction. Option A is wrong because the ores of zinc are zinc blende, which is the sulphide ZnS, and calamine, which is the carbonate ZnCO3. Option C is wrong because tin comes from cassiterite or tin stone, the oxide SnO2, and is refined by liquation. Option D is wrong because mercury comes from cinnabar, the sulphide HgS, and is refined by distillation since it boils at a low temperature. The habit to build is to read the ending of the name: most sulphides of this group end in blende, pyrites, galena or cinnabar, while carbonates end in ite and are calcined rather than roasted.

The correct answer is D, pinna. The pinna is the outer, visible flap of the ear, and its funnel shape collects sound from the surroundings.

Sound gathered by the pinna travels down the ear canal to the tympanic membrane, or eardrum, which starts to vibrate. These vibrations pass through the three small bones of the middle ear, the malleus, incus and stapes, to the cochlea, the coiled fluid filled part of the inner ear. There the vibrations are turned into nerve signals, and the auditory nerve carries them to the brain, where they are recognised as sound.

A is wrong: the auditory nerve carries signals to the brain but does not collect sound. B is wrong: the tympanic membrane vibrates when sound reaches it and does not gather sound itself. C is wrong: the cochlea lies deep inside the ear and changes vibrations into nerve impulses.

Exam tip: the path of sound is pinna, ear canal, eardrum, then malleus, incus and stapes, then cochlea, auditory nerve and brain.

The correct answer is A, Ghee. Calorific value is the heat released on completely burning one gram of a substance, and among the four foods listed ghee has the highest, because it is almost entirely fat. Fats yield roughly nine kilocalories per gram, more than twice what carbohydrates and proteins give, since the carbon and hydrogen in fat are far less oxidised to begin with and so have more energy to release on oxidation. B, maize, and C, rice, are wrong because both are mainly starch, a carbohydrate, which gives about four kilocalories per gram. D, meat, is wrong because it is largely protein and water; protein also gives about four kilocalories per gram, and the water in meat contributes nothing at all. The same reasoning explains why oils and butter are called energy-dense foods and why hydrogen, the lightest and least oxidised fuel, tops the calorific value table for fuels.

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 C, thorium. Homi Bhabha designed the programme around the fact that India has modest uranium but very large thorium reserves in the monazite sands of the Kerala coast. The third stage is to convert thorium into uranium-233 and burn it in reactors designed for that fuel, which would give the country a fuel supply of its own for centuries. Option A is wrong because natural uranium is the fuel of the first stage, burnt in pressurised heavy water reactors. Option B is wrong because plutonium, recovered by reprocessing the spent fuel of the first stage, is the fuel of the second stage in fast breeder reactors such as the prototype at Kalpakkam. Option D is wrong because beryllium is used as a neutron reflector and moderator, not as fuel.

The correct answer is B, sulphide ores. In froth flotation the powdered ore is agitated with water, a frothing agent such as pine oil and a collector. Sulphide particles are preferentially wetted by oil and are carried up with the froth, while the earthy gangue is wetted by water and settles at the bottom, so zinc blende and copper pyrites are concentrated this way. Option A is wrong because oxide ores are usually heavier than the gangue and are concentrated by hydraulic washing, as with haematite and tin stone. Option C is wrong because carbonate ores are not oil-wetted and are normally concentrated by washing before calcination. Option D is wrong because halide ores such as rock salt are soluble in water and are handled by dissolution and crystallisation. A depressant such as sodium cyanide can hold one sulphide back while another floats.

The correct answer is C, the outermost blue non-luminous zone. In this zone the supply of air is unrestricted, so combustion is complete and all the carbon of the fuel is converted to carbon dioxide, releasing the maximum heat. It gives little light and is faintly blue, which is why it is called the non-luminous zone, and a goldsmith directs exactly this part of the flame on gold or silver through a blowpipe to melt it. A is wrong because the innermost dark zone around the wick holds unburnt vaporised wax and receives the least oxygen, making it the coldest part of the flame. B is wrong because the middle yellow zone shows only partial combustion, where glowing unburnt carbon particles give the flame its light but not its greatest heat. D is wrong because the three zones differ sharply in both temperature and composition, and the whole point of studying flame structure is that difference.

The correct answer is B. Calcination is the heating of an ore in the absence or a limited supply of air and below its melting point, so that water of hydration and carbon dioxide are driven off; it is therefore the step used for carbonate ores such as calamine and for hydrated ores such as bauxite. Option A is wrong because heating in a plentiful supply of air is roasting, which is applied to sulphide ores such as zinc blende, where sulphur escapes as sulphur dioxide. Option C is wrong because adding a reducing agent such as coke is the separate step of smelting or reduction, which comes after calcination or roasting. Option D is wrong because both calcination and roasting are deliberately carried out below the melting point; melting the ore is the business of smelting. Both steps share one aim, to obtain the oxide, which is the form easiest to reduce.