General Science Mixed Quiz: Set 36

The correct answer is B, Magnetic field strength (H). Ampere-turns per metre, written AT/m, is the unit of magnetic field strength, because H is the magnetomotive force set up per unit length of the magnetic path. In a coil the magnetomotive force equals the current multiplied by the number of turns and is measured in ampere-turns; divide that by the length of the magnetic circuit and the result is H, which is why the unit carries a metre in the denominator. H is also called magnetising force, and in air it is linked to flux density by B equal to the permeability times H. A is wrong because magnetic flux density B is measured in tesla, that is weber per square metre. C is wrong because magnetic flux is measured in weber. D is wrong because magnetomotive force itself is measured in ampere-turns, with no length divided out. Exam tip: ampere-turn is magnetomotive force, ampere-turn per metre is field strength H, weber is flux and tesla is flux density.

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 C, Velocity and time. The first equation of motion is written as v equals u plus a t, so it tells how the velocity of a body changes with time. Here u is the initial velocity, v the velocity after time t and a the uniform acceleration. All three equations of motion hold only for straight-line motion with constant acceleration. A is wrong because the link between position and time is the second equation, s equals u t plus half a t squared. B is wrong because the link between position and velocity is the third equation, v squared equals u squared plus two a s, which has no time term. D is wrong because acceleration appears in all three equations but none of them connects velocity with acceleration alone; either time or displacement must come in. Exam tip: remember the three as velocity-time, position-time and velocity-position in that order.

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 A, The principle of conservation of energy is not violated. As the body falls its height shrinks, so the potential energy m g h falls, but exactly that much energy reappears as kinetic energy, half m v squared, because the body speeds up. The sum of the two stays the same at every point of the fall, so the total mechanical energy is conserved and energy is only changing form. At the moment of release the energy is all potential; just before the body strikes the ground it is almost all kinetic. When air resistance acts, the small shortfall leaves as heat and sound, so the energy is still accounted for. B is wrong because no energy is destroyed, only converted. C and D are wrong because gravity is a force, not a law that can be obeyed or broken, and neither statement answers what happens to the lost potential energy. Exam tip: for free fall, m g h plus half m v squared stays constant.

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, Weight. The weight of an object is the force with which the earth attracts it, so the force of gravity acting on an object is its weight. Weight is calculated as W equals mg, where m is the mass of the body and g is the acceleration due to gravity, about 9.8 metre per second squared at the surface of the earth. Weight is a force, so it is a vector quantity and its SI unit is the newton. Because g changes from place to place, the same object weighs a little less at the equator than at the poles and about one sixth as much on the moon, while its mass stays exactly the same. A is wrong because impulse is force multiplied by the time for which it acts, and it changes the momentum of a body. B is wrong because mass is the quantity of matter in a body, a scalar measured in kilograms, which does not change with place. C is wrong because acceleration is the rate of change of velocity. Exam tip: mass in kilograms never changes, weight in newtons changes with g.

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 B, Water - 1200. Water has a specific heat capacity of about 4186 joule per kilogram per kelvin, not 1200, so this pair is the wrong one. Specific heat capacity is the heat needed to raise the temperature of one kilogram of a substance by one kelvin, and water's value is the highest among common liquids. That is why water is used as a coolant in car radiators and industry, why the sea warms and cools slowly, and why coastal places have a milder climate than inland towns. A is a correct pair because aluminium takes about 900 joule per kilogram per kelvin. C is a correct pair because carbon in its graphite form is close to 506.5. D is a correct pair because tungsten, a heavy metal, needs only about 134.4, so metals heat up quickly. Exam tip: remember water as about 4186 joule per kilogram per kelvin, which is one calorie per gram per degree Celsius.

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, +3. The object stands between the pole and the focus of the concave mirror, so the image formed is virtual, erect and enlarged, and the magnification is positive. Using the sign convention, u is -12 cm and f is -18 cm. From the mirror formula, 1/v + 1/u = 1/f, we get 1/v = 1/f - 1/u = -1/18 + 1/12 = 1/36, so v = +36 cm, an image formed 36 cm behind the mirror. Magnification m = -v/u = -36 divided by -12, which is +3, so the image is three times the size of the object. This is exactly why a concave mirror is used as a shaving mirror and by dentists. A is wrong because a negative magnification means a real and inverted image, which a concave mirror gives only when the object lies beyond the focus. C is wrong for the same reason. D is wrong because an image smaller than the object is never formed in this position. Exam tip: an object inside the focus of a concave mirror always gives a virtual, erect and magnified image.

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 A, Frequency. Pitch is how shrill or how flat a sound seems to the ear, and it is decided by frequency, the number of vibrations per second measured in hertz. A higher frequency gives a shriller sound, so a whistle or a woman's voice has a higher pitch than a drum or a man's voice; the human ear hears roughly 20 to 20000 hertz. B is wrong because wavelength changes with the medium the sound travels through, while the pitch a listener hears stays the same, so frequency and not wavelength fixes pitch. C is wrong because amplitude decides loudness, which is why striking a drum harder makes it louder but not shriller. D is wrong because timbre, or quality, is what lets us tell a flute from a violin playing the same note at the same loudness. Exam tip: frequency gives pitch, amplitude gives loudness and waveform gives quality.

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 B, 540 cal. The heat produced by a current is given by Joule's law of heating, H equals I squared into R into t. Here the current is 0.3 A, the resistance is 418 ohms and the time is 1 minute, which is 60 seconds. So H = 0.09 into 418 into 60 = 2257.2 joule. One calorie equals 4.18 joule, so 2257.2 divided by 4.18 gives 540 calorie. Joule's law says the heat produced is proportional to the square of the current, to the resistance and to the time, which is why doubling the current gives four times the heat. The same law explains the electric iron, the heater, the geyser, the filament of a bulb and the fuse that melts to protect a circuit. A is wrong because 360 calorie would need a current of about 0.245 A for the same resistance and time. C is wrong because it is one tenth of the correct value. D is wrong because 36 calorie would need a current of only about 0.077 A. Exam tip: use H equals I squared Rt, then divide the joule figure by 4.18 to get calories.

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 D, s. The element with atomic number 56 is barium, and its outermost electron enters the 6s orbital, so it sits in the s-block. Barium has the configuration of xenon followed by 6s2, which places it in group 2 of the periodic table along with the other alkaline earth metals such as calcium and strontium. The block of an element is decided by the sub-shell that receives the last electron: groups 1 and 2 plus helium form the s-block, groups 13 to 18 the p-block, groups 3 to 12 the d-block, and the lanthanoids and actinoids the f-block. A is wrong because p-block elements end in a p sub-shell. B is wrong because f-block elements are the inner transition metals. C is wrong because d-block elements are the transition metals of groups 3 to 12. Exam tip: atomic number 56 is barium, group 2, s-block.

The correct answer is C, neutralisation reaction. In the given equation sodium hydroxide, which is a base, reacts with sulphuric acid to give sodium sulphate and water, and a reaction in which an acid and a base cancel each other to form a salt and water is called neutralisation. Its general form is acid plus base gives salt plus water, and heat is given out, so the reaction is exothermic. Two molecules of sodium hydroxide are needed here because sulphuric acid is dibasic and supplies two hydrogen ions. Everyday examples are an antacid taken for acidity in the stomach, lime spread on an acidic soil and baking soda rubbed on a bee sting. A is wrong because a precipitation reaction forms an insoluble solid, while both products here stay in solution. B is wrong because in a decomposition reaction a single compound splits into two or more simpler substances. D is wrong because a redox reaction involves a change in oxidation numbers, and here they do not change. Exam tip: acid plus base giving salt and water is always neutralisation.

The correct answer is D, Dilution. Adding water to an acid spreads the same number of hydrogen ions through a larger volume, so the number of hydrogen ions per unit volume falls, and that process is called dilution. A dilute acid therefore acts less strongly than a concentrated one, even though the acid itself is the same substance. Dilution of a strong acid is exothermic, so acid is always added slowly to water with constant stirring, never water to acid, or the heat released can make the mixture splash out. The same idea applies to bases, where dilution lowers the number of hydroxide ions per unit volume. A is wrong because concentration means increasing the amount of acid in a given volume, which is the opposite of what happens here. B is wrong because acidification means making a substance acidic, not thinning an acid that is already there. C is wrong because neutralisation is the reaction of an acid with a base to give a salt and water. Exam tip: always add acid to water, never water to acid.

The correct answer is B, graphite. Graphite is an allotrope of carbon in which each atom is bonded to three others, leaving one electron per atom free to move through the layers, so it conducts electricity although it is a non-metal; this is why graphite is used for electrodes and in dry cells. Option A, sulphur, is a brittle, non-conducting solid, the standard example of non-metallic behaviour. Option C, phosphorus, does not conduct and its white form is stored under water because it ignites in air. Option D, iodine, is the non-metal that is lustrous, so it is the exception to a different rule and a favourite distractor here. Note also diamond, the other allotrope of carbon: it is the hardest natural substance and conducts heat extremely well, but it does not conduct electricity.