General Science Mixed Quiz: Set 61

The correct answer is A, hydraulic brakes. Pascal's law says that pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid and to the walls of the vessel, so a modest push on the brake pedal creates a pressure in the brake fluid that is passed to the wider pistons at every wheel, where it becomes a large force. The hydraulic lift and the hydraulic press work the same way. Option B is wrong because a barometer measures atmospheric pressure by balancing it against a column of mercury. Option C is wrong because a hydrometer floats in a liquid and measures relative density, which rests on the law of flotation. Option D is wrong because a siphon works on the difference in pressure caused by the difference in the height of the two liquid levels.

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, dioptre. The power of a lens measures how strongly it converges or diverges light, and it is defined as one divided by the focal length expressed in metres. Since the focal length is in metres, the unit of power is the reciprocal metre, which is given the special name dioptre and the symbol D. Option A is wrong because the newton is the unit of force and has nothing to do with the focusing strength of a lens. Option C is wrong because the lumen measures luminous flux, that is the total visible light given out by a source. Option D is wrong because the candela is the base unit of luminous intensity, the light emitted by a source in a particular direction. Only the dioptre is a property of the lens itself rather than of the light.

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, pascal second, equal to a newton second per square metre, which follows from Newton's law of viscosity, where the shearing stress in pascals is divided by the velocity gradient in reciprocal seconds. Option A, the poise, is wrong because it is the CGS unit of the same quantity, and one pascal second equals ten poise. Option C, stokes, is wrong because it is the CGS unit of kinematic viscosity, which is the coefficient of viscosity divided by the density and is measured in square metres per second in SI units. Option D, newton per metre, is wrong because it is the unit of surface tension, a force per unit length, and the pairing of surface tension with viscosity is a favourite way of setting a trap in this chapter.

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 B, minus 2 dioptres. Two steps are needed. First, the focal length must be converted to metres: 50 centimetres is 0.5 metre. Second, the power is one divided by the focal length in metres, which gives two dioptres in magnitude. Finally the sign convention is applied: a concave or diverging lens always has a negative focal length and therefore a negative power, so the answer is minus 2 D. Option A has the right magnitude but the wrong sign, and would describe a convex lens of the same focal length. Option C comes from forgetting to convert centimetres to metres and dividing by 2 instead, and option D repeats that error with the correct sign. Candidates who keep the unit conversion and the sign convention separate rarely lose this mark.

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, surface tension. Cohesive forces pull the molecules at the surface of a liquid inward, so the surface behaves like a stretched membrane and takes the smallest area that can enclose the given volume; for a fixed volume the shape of least surface area is a sphere, which is why a free drop and a soap bubble are both round. Option A, viscosity, is wrong because it governs resistance to flow and so decides the speed of falling, not the shape. Option C, capillarity, is wrong because it is a consequence of surface tension together with adhesion, and describes the rise or fall of a liquid in a narrow tube rather than the shape of a drop. Option D, buoyancy, is wrong because it is the upthrust of a surrounding fluid and explains floating, not shape; large falling drops are in fact flattened by air resistance.

The correct answer is C, 1.6 sec. Time period is the time taken for one full oscillation, so it is the total time divided by the number of oscillations: 64 divided by 40 gives 1.6 seconds. Frequency is the reverse quantity, the number of oscillations in one second, which here is 40 divided by 64, or 0.625 hertz; period and frequency are always reciprocals of each other. For a simple pendulum the period depends only on the length of the thread and on the acceleration due to gravity, through T equal to 2 pi times the square root of L by g. It does not depend on the mass of the bob, nor, for small swings, on how wide the swing is. A pendulum about one metre long has a period of close to two seconds. A is wrong because 0.6 second would give more than 100 oscillations in 64 seconds. B and D are wrong because 6 and 16 seconds are far too long for 40 swings in just over a minute. Exam tip: time period equals total time divided by the number of oscillations.

The correct answer is D, violet. The refractive index of a transparent medium is not the same for every colour; it rises as the wavelength falls. Violet has the shortest wavelength among the visible colours, so glass offers it the highest refractive index, it bends the most at both faces of the prism and it emerges with the greatest deviation. That is why violet lies at the lower end of the spectrum on the screen. Option A is the opposite case: red has the longest wavelength, the lowest refractive index in glass and therefore the least deviation. Options B and C, yellow and green, lie between red and violet in wavelength and so are deviated by intermediate amounts, more than red but less than violet. Remembering VIBGYOR with violet deviated most settles every question of this family.

The correct answer is C, Stapedius. The stapedius, only about 1 millimetre long, is the smallest skeletal muscle in the human body. It lies in the middle ear and is attached to the stapes, which is itself the smallest bone of the body. When a very loud sound reaches the ear, the stapedius contracts and damps the vibration of the stapes, protecting the delicate inner ear; this is called the acoustic reflex. It is supplied by the facial nerve, so damage to that nerve can make ordinary sounds seem painfully loud. Option A is wrong because the biceps is a large muscle at the front of the upper arm that bends the elbow. Option B is wrong because the sartorius, which runs across the thigh, is the longest muscle of the body, not the smallest. Option D is wrong because the triceps at the back of the upper arm straightens the elbow and is a large muscle. Exam tip: smallest muscle stapedius, smallest bone stapes, longest muscle sartorius, largest muscle gluteus maximus.

The correct answer is C. In a liquid, viscosity comes chiefly from cohesion between molecules; heating weakens that cohesion, so the layers slide past one another more easily and the viscosity falls, which is why engine oil becomes thinner as the engine warms and why honey flows freely when it is warmed. In a gas, viscosity comes from the transfer of momentum by molecules moving between layers; heating makes those molecules move faster, so more momentum is carried across and the viscosity rises. Option A and option B are wrong because they treat the two states alike. Option D is wrong because it reverses both results. This contrast is one of the most frequently asked single facts from the chapter and is worth memorising as a pair.

The correct answer is A, Gamma rays. Gamma rays are electromagnetic waves of the highest frequency and shortest wavelength, given out by the nucleus of a radioactive atom and in nuclear reactions, and their energy lets them kill cancer cells in radiotherapy. Cobalt-60 is the source used in the gamma knife and in the teletherapy units of Indian hospitals; gamma rays also sterilise surgical instruments and are used to preserve onions and potatoes. They carry no charge and no mass, so a magnetic field does not bend them, and only thick lead or concrete stops them. B is wrong because ultraviolet waves come from the Sun and from lamps, and are much weaker. C is wrong because visible light is the narrow band our eyes can see. D is wrong because X-rays come from electrons striking a metal target outside the nucleus, not from the nucleus itself. Exam tip: the order of increasing frequency is radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.

The correct answer is B, cone cells. The retina carries two kinds of photoreceptor. Cone cells need reasonably bright light to work and respond selectively to different wavelengths, so they give us the sensation of colour; when the cones are defective a person is colour blind. Option A is wrong because rod cells are sensitive to very dim light but cannot distinguish wavelengths, which is why colours fade and the world looks grey at dusk when only the rods are working. Option C is wrong because goblet cells are mucus-secreting cells of the lining of the intestine and the respiratory tract and are not found in the retina. Option D is wrong because mast cells belong to the immune system and release histamine during allergic reactions. Only rods and cones are retinal receptors, and of these only the cones see colour.

The correct answer is C, butane and propane. The LPG supplied in household cylinders is mainly a mixture of butane and propane, two gases that turn liquid under moderate pressure. Both are saturated hydrocarbons got while refining crude oil or processing natural gas, and because they liquefy on compression, a cylinder holds far more fuel than the same volume of gas would. The gases have no smell of their own, so a strong-smelling compound called ethyl mercaptan is added to make a leak noticeable at once. LPG burns with a clean blue flame and leaves almost no residue, which makes it a far better home fuel than wood or coal. A is wrong because methane is the chief part of CNG and biogas, not of LPG. B is wrong because ethane is at most a minor component. D is wrong because hexane is a liquid at room temperature and serves as a solvent. Exam tip: LPG is butane plus propane, while CNG is mainly methane.

The correct answer is C, it remains unchanged. While the ice floats it displaces a volume of water whose weight equals the weight of the ice, by the law of flotation. When the ice melts it becomes water of exactly that weight, and water of that weight occupies exactly the volume the floating ice was displacing, so the level neither rises nor falls. Option A is wrong because the melted water fills the space the submerged part of the ice occupied and adds nothing further. Option B is wrong because no water leaves the glass. Option D is wrong because the balance holds throughout the melting, so there is no intermediate change. If the ice contained a stone or a cork the answer would differ, and that is the version examiners use to catch candidates who have learnt the result without the reasoning.

The correct answer is C, Bakelite. Bakelite is a thermosetting polymer, made by condensing phenol with formaldehyde, and once it has set under heat its chains are cross-linked, so it cannot be melted and moulded again. That hardness and poor conduction of heat and electricity are why bakelite is used for switches, plugs, handles of pans and radio cabinets; it was prepared by Leo Baekeland and was the first fully synthetic plastic. Melamine and urea-formaldehyde resins behave in the same way. A is wrong because polythene is a thermoplastic that softens on heating and can be recycled into new articles. B is wrong because PVC is also a thermoplastic, used for pipes, cable covers and raincoats. D is wrong because neoprene is a synthetic rubber, that is an elastomer, valued for resisting oil and petrol. Exam tip: thermosetting means bakelite, melamine and urea-formaldehyde; thermoplastic means polythene, PVC and polystyrene.

The correct answer is B, a convex lens. In hypermetropia the eye lens is too weak or the eyeball is too short, so rays from a nearby object are not converged enough and the image falls behind the retina. A convex or converging lens of suitable positive power brings the rays together a little before they enter the eye, so the eye lens can now form the image exactly on the retina and the near point returns to about 25 centimetres. Option A is wrong because a concave lens diverges light further and is the correction for myopia, the opposite defect. Option C is wrong because a cylindrical lens corrects astigmatism, where the cornea is not perfectly spherical. Option D is wrong because a plane mirror only reflects light without converging or diverging it and cannot change where an image forms inside the eye.

The correct answer is C, scattering of light. The molecules of the atmosphere are much smaller than the wavelength of visible light, and such particles scatter short wavelengths far more strongly than long ones. Blue light from the sun is therefore thrown sideways again and again and reaches the eye from every direction in the sky, which makes the sky look blue; the same mechanism makes the setting sun look red. Option A is wrong because dispersion needs refraction through a medium that separates colours, as in a prism or a raindrop forming a rainbow. Option B is wrong because total internal reflection explains mirages, optical fibres and the sparkle of a diamond, not the colour of the sky. Option D is wrong because interference explains the colours of soap bubbles and oil films, which arise from thin layers rather than from the open atmosphere.