General Science Mixed Quiz: Set 60

The correct answer is A, one to eight by mass. A molecule of water contains two atoms of hydrogen and one of oxygen. Taking the atomic masses as one for hydrogen and sixteen for oxygen, the two hydrogen atoms contribute two units of mass and the oxygen atom sixteen, so the ratio by mass is two to sixteen, which reduces to one to eight. Option B, eight to one by mass, is the same figure with the order reversed, and reversing it is the commonest mistake, so note that oxygen is the heavier part. Options C and D confuse mass with volume: by volume, or equivalently by the number of atoms, hydrogen and oxygen are in the ratio of two to one, which is what the formula for water states directly. A fixed ratio of this kind is exactly what makes water a compound rather than a mixture, and it holds for every sample of pure water from any source.

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 D. By Archimedes' principle the upthrust on a body equals the weight of the fluid it displaces, and that weight is the volume of the body actually immersed multiplied by the density of the fluid and by the acceleration due to gravity. Only those two properties of the situation enter the expression. Option A is wrong because the weight of the body decides whether it floats or sinks but not the size of the upthrust; a kilogram of lead and a kilogram of cork displace very different volumes. Option B is wrong because shape matters only in so far as it changes the volume immersed; a lump and a sheet of the same metal fully submerged receive the same upthrust. Option C is wrong because it replaces volume with mass, and two bodies of equal mass but different density displace different volumes of fluid.

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 C. Myopia, or short-sightedness, is the defect in which nearby objects are seen clearly but distant objects look blurred. It arises either because the eye lens has become too converging, that is its focal length is too short, or because the eyeball has grown too long from front to back. In such an eye the rays from a distant object converge too early and the image falls in front of the retina, not beyond it, so statement C is the incorrect one and is therefore the answer. Option A is a correct statement, because a concave or diverging lens of suitable negative power moves the image back on to the retina. Option B is correct, since near sightedness is simply the common English name for myopia. Option D is also correct, because the far point of a myopic eye shifts in from infinity to a few metres.

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 D, only B, that is a liquid. A colloid is named according to the states of its two parts, the dispersed phase and the dispersing medium, and an emulsion is defined as a colloid in which a liquid is dispersed in another liquid, so the dispersing medium must itself be a liquid. Milk, in which fat globules are dispersed in water, and butter, in which water is dispersed in fat, are the standard examples. Option B, only A, names a gas, but a liquid dispersed in a gas is an aerosol, which is what fog, mist and a cloud are, and not an emulsion. Option A, A and C only, names a gas and a solid, so it rules out the one correct medium. Option C, B and C only, correctly includes liquid but wrongly adds solid, and a liquid dispersed in a solid is called a gel, as in cheese and jelly. Fix the set as sol for a solid in a liquid, emulsion for a liquid in a liquid, aerosol for either in a gas and gel for a liquid in a solid.

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, 8 per cent. A floating body displaces its own weight of fluid, so the fraction of its volume that lies below the surface equals the ratio of its density to the density of the fluid, here 920 divided by 1000, which is 0.92. That means 92 per cent of the iceberg is submerged and the remaining 8 per cent stands above the water. Option A, 6 per cent, is wrong because it would require an ice density of 940 kilograms per cubic metre. Option C, 92 per cent, is wrong because that is the submerged fraction, and it is the commonest error in this question, since the candidate stops one step too early. Option D, 20 per cent, is wrong by a wide margin and would need a density ratio of 0.8. The same calculation explains why only the tip of an iceberg is seen at sea.

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.

The correct answer is B, cornea. The cornea is the thin, transparent, slightly bulging membrane that forms the front surface of the eyeball, and light must pass through it before reaching anything else. Because the change of medium from air to cornea is the sharpest in the whole eye, most of the refraction of incoming light also happens here. Option A is wrong because the retina is the light-sensitive screen at the back of the eye on which the image is finally formed, so light reaches it last and not first. Option C is wrong because the pupil is not a membrane at all but an opening, the central hole through which light passes after crossing the cornea. Option D is wrong because the iris is the coloured muscular curtain that widens or narrows the pupil to control the quantity of light entering the eye.

The correct answer is D, Charles’s law. Charles’s law says that at constant pressure the volume of a fixed mass of gas is directly proportional to its absolute temperature, so V by T stays constant. Jacques Charles studied this in 1787, and Joseph Gay-Lussac published the quantitative form in 1802. Written as a ratio it gives V1 by T1 equals V2 by T2, with the temperature always taken in kelvin. Extending the volume-temperature graph backwards to zero volume gives absolute zero, minus 273.15 degrees Celsius, which is how the kelvin scale was fixed. A is wrong because Boyle’s law relates pressure and volume at constant temperature, with PV constant. B is wrong because Dalton’s law of partial pressures adds the pressures of the gases in a mixture. C is wrong because Avogadro’s law links equal volumes of gases to equal numbers of molecules. Exam tip: keep the three apart - Boyle for P and V, Charles for V and T, Gay-Lussac for P and T.

The correct answer is B, the centre of mass of the displaced fluid. The upthrust on a body is the resultant of the pressure forces of the fluid around it, and that resultant acts through the centre of gravity of the fluid the body has pushed aside, which is why the point is called the centre of buoyancy. Option A is wrong because the centre of gravity of the body depends on how the body's own mass is distributed, and the two points coincide only when the body is of uniform density and fully submerged. Option C is wrong because the metacentre is a separate point, defined where the line of the upthrust cuts the centre line of a slightly tilted body, and it lies above the centre of gravity in stable flotation. Option D describes the metacentre rather than the centre of buoyancy.

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, interference. A soap film is extremely thin, and light reflected from its front surface meets light reflected from its back surface. The two waves have travelled slightly different distances, so for each wavelength they either reinforce or cancel one another. This thin-film interference strengthens one colour and removes another at every point of the film, which is why a bubble shows shifting bands of colour. Option A, scattering, is wrong because scattering redirects light by particles and explains the blue sky and the red sunset, not the colours of a film. Option C, dispersion, is wrong because dispersion separates colours by refraction through a medium such as a prism or a raindrop, and a soap film is too thin to disperse light this way. Option D, diffraction, is wrong because that is the bending of light around obstacles and through narrow slits, as in a CD track or a grating.

The correct answer is D, stomata. The tiny pores on the surface of a leaf, found mostly on its lower side, are called stomata.

Each stoma is a slit guarded by two bean shaped guard cells, which swell to open it and shrink to close it. Through these pores the plant takes in carbon dioxide for photosynthesis and gives out oxygen, and water vapour escapes through them in the process called transpiration. Having them on the shaded lower surface reduces the loss of water. Floating plants such as the water lily carry their stomata on the upper surface instead, and fully submerged plants have almost none.

A is wrong: pore is only the general word for an opening and is not the botanical term. B is wrong: opening is likewise a plain description, not a name. C is wrong: cilia are tiny hair like structures that help some cells and organisms move, and they are not found on leaves.

Exam tip: stomata are leaf pores guarded by guard cells, mostly on the lower surface, used for gas exchange and for transpiration.

The correct answer is D, a Newtonian fluid. In such a fluid the shearing stress is directly proportional to the rate of shear, so the coefficient of viscosity, which measures the resistance to deformation, keeps the same value whatever the stress applied; water, air, petrol and thin oils behave in this way. Option A, a Bingham plastic, is wrong because it will not flow at all until a yield stress is exceeded, toothpaste being the familiar example. Option B, a pseudoplastic fluid, is wrong because its apparent viscosity falls as the shear rate rises, which is how paint spreads when it is brushed. Option C, a dilatant fluid, is wrong because its apparent viscosity rises with the shear rate, as in a thick paste of cornflour and water that hardens when struck. The last three are grouped together as non-Newtonian fluids.

The correct answer is B, the iris. The iris is the coloured ring of muscle lying just behind the cornea. By contracting and relaxing it makes the central opening, the pupil, smaller in bright light and larger in dim light, and in this way it regulates how much light falls on the retina. Option A is wrong because the cornea is the fixed transparent front membrane; it refracts light strongly but cannot change the size of any opening. Option C is wrong because the retina is the screen of rod and cone cells at the back of the eye where the image is formed and converted into nerve signals. Option D is wrong because the ciliary muscles act on the crystalline lens, changing its curvature and focal length to focus objects at different distances, which is accommodation and not light control.

The correct answer is C. In a capillary tube the height of rise is directly proportional to the surface tension of the liquid and inversely proportional to its density and the radius of the tube. If a liquid climbs higher than water in the same tube, the most natural explanation is that its surface tension is greater than that of water, which is the same as saying that the surface tension of water is less than that of the liquid. Option D states the relation the wrong way round and would make the liquid rise less than water. Option A is wrong because viscosity decides how fast the liquid rises, not how far; the final height is a matter of equilibrium. Option B is wrong because raising the temperature lowers surface tension, which would reduce the rise rather than increase it.

The correct answer is C, 25 cm. The least distance of distinct vision, also called the near point, is the smallest distance at which an object can be held and still be seen clearly without strain. For a normal adult eye this distance is taken as about 25 centimetres, and it is the standard value used in every numerical problem on magnifying glasses and microscopes. Option A, 10 cm, is closer than an adult eye can comfortably focus, although a young child can manage something near it. Option B, 15 cm, is likewise too small for the standard adult value. Option D, 50 cm, is far beyond the near point of a healthy eye and is nearer to the receded near point of a person with hypermetropia or presbyopia, whose ciliary muscles can no longer thicken the lens enough.