General Science Mixed Quiz: Set 27

The correct answer is A, Poise. Dynamic viscosity measures how strongly a fluid resists flowing, and in the centimetre gram second system it is measured in poise, a unit named after the French physician Jean Louis Marie Poiseuille, who studied the flow of blood in narrow tubes. One poise is one dyne second per square centimetre, and since the SI unit is the pascal second, one pascal second equals ten poise. Thin liquids are usually quoted in centipoise: water at room temperature is about one centipoise while honey runs into thousands. Option B is wrong because the pascal second is the SI unit of dynamic viscosity, and the question asks for the CGS unit. Option C is wrong because the stoke is the CGS unit of kinematic viscosity, which is dynamic viscosity divided by density. Option D is wrong because option A already names the right unit. Exam tip: dynamic viscosity in poise and pascal second, kinematic viscosity in stoke and square metre per second.

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, 45 degree with the ground. Once the athlete's feet leave the ground they move as a projectile, and the horizontal distance covered, called the range, is given by R equal to u squared into sin 2 theta divided by g. The range is largest when sin 2 theta has its greatest value of one, which happens when 2 theta is 90 degrees, so the angle of projection theta must be 45 degrees. The same formula shows that two angles adding up to 90 degrees give equal ranges. Option A is wrong because a take-off straight up at 90 degrees sends the jumper vertically and the range falls to zero, though the height is the greatest. Option B is wrong because 60 degrees buys height at the cost of distance. Option D is wrong because 30 degrees keeps the jump flat and short, and it covers exactly the same distance as 60 degrees. Exam tip: maximum range at 45 degrees, maximum height at 90 degrees, and complementary angles share a range.

The correct answer is B, tuberculosis (TB). The BCG vaccine takes its name from Albert Calmette and Camille Guerin, the two French scientists who developed it from a weakened strain of Mycobacterium bovis. In India it is given as a single dose soon after birth under the Universal Immunisation Programme, and it protects infants mainly from the severe forms of the disease, such as tuberculous meningitis and miliary tuberculosis. Tuberculosis itself is caused by the bacterium Mycobacterium tuberculosis, identified by Robert Koch in 1882, and it spreads through droplets when a patient coughs. Option A is wrong because typhoid, caused by Salmonella typhi, has its own conjugate vaccine. Option C is wrong because mumps is a viral disease covered by the MMR vaccine along with measles and rubella. Option D is wrong because plague, caused by Yersinia pestis and carried by rat fleas, needs a different vaccine. Exam tip: BCG at birth for TB, and World TB Day falls on 24 March.

The correct answer is D, the speed is less than the square root of 2gh. A body that slides down a smooth slope turns all of its potential energy mgh into translational kinetic energy and reaches the bottom with a speed equal to the square root of 2gh. A cylinder that rolls without slipping must also spin, so the same mgh has to be shared between translation and rotation, and the speed of its axis is bound to come out smaller. Working it out for a solid cylinder, mgh equals half m v squared plus one fourth m v squared, which gives v as the square root of four gh by three, about 1.15 times the square root of gh against 1.41 for the sliding body. Option A is wrong because gh is not even a speed, as the units do not match. Option B is wrong because mgh is an energy and the mass cancels out in any case. Option C is wrong because that value belongs to a body that slides without rotating. Exam tip: of bodies rolling down the same slope, a solid sphere beats a solid cylinder, which beats a ring.

The correct answer is B, Rod-shaped. Bacteria are grouped by shape, and bacilli are the rod-shaped ones; the Latin word bacillus itself means a small rod or stick. Tuberculosis, tetanus, typhoid and anthrax are all caused by rod-shaped bacteria, and Lactobacillus, the bacterium that curdles milk into curd, belongs to the same group. The other shapes in this classification are cocci, which are spherical, spirilla, which are long and spiral, and vibrio, which are curved like a comma. A is wrong because comma-shaped bacteria are called vibrio, the best known being Vibrio cholerae, which causes cholera. C is wrong because spiral bacteria are spirilla and spirochaetes. D is wrong because spherical bacteria are cocci, such as Streptococcus. Exam tip: cocci are round, bacilli are rods, spirilla are spirals and vibrio are comma-shaped.

The correct answer is B, absolute pressure. Pressure counted from a perfect vacuum as the zero point is called absolute pressure. A perfect vacuum holds no gas and exerts no pressure, so it is the true zero of any pressure scale. The working relation is absolute pressure = gauge pressure + atmospheric pressure, and atmospheric pressure at sea level is about 101.3 kilopascals, or 760 mm of mercury. So a tyre whose gauge reads 200 kPa is really at about 301 kPa absolute. Gas laws and thermodynamic formulas always take absolute pressure, which is why the distinction is tested. Option A is wrong because gauge pressure takes atmospheric pressure as its zero, so an open gauge reads zero even though air is pressing on it. Option C is wrong because atmospheric pressure is the weight of the air column itself, read on a barometer. Option D is wrong because 'absolute zero pressure' names the vacuum, the reference point, not the reading taken from it. Exam tip: absolute = gauge + atmospheric; a reading below atmospheric is vacuum or negative gauge pressure.

The correct answer is A, a suspension is a heterogeneous mixture. In a suspension the particles of the solute are large enough to be seen and do not dissolve; they stay spread through the liquid only while it is stirred and settle to the bottom when it is left standing. Chalk powder in water, muddy river water and a shaken bottle of paint are everyday examples. Because the particles are big, a suspension scatters a beam of light, showing the Tyndall effect, and the particles can be separated by filtration. B is wrong because solids spread in a gas, such as smoke, are aerosols, a kind of colloid, not a suspension. C is wrong because the particles of a suspension are large enough to be seen with the naked eye; it is the particles of a solution that cannot be seen. D is wrong because a homogeneous mixture is a solution, which is uniform throughout. Exam tip: solution homogeneous, suspension heterogeneous and settles, colloid in between.

The correct answer is A, the air pressure is less. A liquid boils when its vapour pressure equals the pressure of the air pressing on its surface, so lower air pressure means a lower boiling point. At sea level the atmosphere presses with about 101 kilopascals and water boils at 100 degrees Celsius. On a hill station the column of air above is shorter, the pressure falls, and water may boil at 90 degrees or less, which is why rice and pulses cook slowly in the mountains and a pressure cooker, which raises the pressure inside, is used to cook them faster. Option B is wrong because the surrounding temperature only decides how long heating takes, not the temperature at which boiling begins. Option C is wrong because the latent heat of vaporisation is a property of water and does not shrink with altitude. Option D is wrong because option A already states the correct reason. Exam tip: boiling point rises with pressure and falls with altitude; that single rule explains both the cooker and the hill station.

The correct answer is B, Abscisic acid. Abscisic acid is the one plant hormone in this list that slows growth instead of speeding it up, which is why it is often called the stress hormone of plants. It causes the closing of stomata when water is short, keeps seeds and buds dormant until conditions are right, and helps leaves and fruit fall. The other three are growth promoters. A is wrong because cytokinins encourage cell division and delay the ageing of leaves. C is wrong because gibberellins cause stems to lengthen, break seed dormancy and make some plants flower early. D is wrong because auxins make cells elongate and are the hormone behind phototropism, the bending of a shoot towards light, since auxin gathers on the shaded side. All four are chemical messengers made in one part of the plant and acting in another. Exam tip: abscisic acid alone inhibits; auxin, gibberellin and cytokinin promote growth.

The correct answer is D, Polarization. Only a transverse wave can be polarised, so the polarisation of light proves that its vibrations are at right angles to the direction of travel. In ordinary light the electric field vibrates in every plane around the ray. A polaroid sheet lets through only the vibrations in one plane, and a second polaroid turned at ninety degrees then blocks the light completely. A longitudinal wave such as sound, whose particles vibrate along the direction of travel, has no such plane and can never be polarised. Sunglasses, camera filters and LCD screens all use this property. Option A is wrong because refraction, the bending of light on entering a denser medium, happens with sound waves too. Option B is wrong because diffraction, the spreading of a wave at an edge, is shown by all waves. Option C is wrong because interference only proves that light is a wave, not which kind. Exam tip: interference and diffraction prove light is a wave; polarisation proves it is a transverse wave.

The correct answer is C, increases. Water behaves unlike most liquids between 0 and 4 degrees Celsius, a behaviour called the anomalous expansion of water. Almost every substance shrinks as it is cooled, but water shrinks only until it reaches 4 degrees Celsius. At that temperature it has its smallest volume and therefore its greatest density, about one gram per cubic centimetre. Cool it further, from 4 degrees down to 0 degrees, and it expands again, so one litre takes up more space at 0 degrees than at 4 degrees. This is why ice floats and why, in winter, a lake freezes only at the top while the water below stays at about 4 degrees, allowing fish to live through the cold. A and D are wrong because water only expands over this range, it does not shrink. B is wrong because the volume clearly changes. Exam tip: water is densest at 4 degrees Celsius.

The correct answer is C, decibel. The loudness or intensity level of sound is measured in decibels (dB), a unit named after Alexander Graham Bell. The decibel is a logarithmic unit, so every rise of 10 dB means the intensity of the sound has become ten times greater; that is why a whisper of about 30 dB and ordinary talk of about 60 dB feel so far apart. City traffic runs at about 80 dB, a sound above 120 dB is painful to the ear, and India's noise pollution rules are themselves written in dB for day and night limits. Option A is wrong because the hertz measures frequency, the number of vibrations a second, which the ear hears as pitch and not as loudness. Option B is wrong because wave number counts how many waves fit into a unit length and is used in spectroscopy, not for measuring sound. Option D is wrong for the same reason, since cm -1 is only the unit in which wave number is written. Exam tip: pitch goes with hertz, loudness with decibel.

The correct answer is D, Above the center of gravity. When a floating body tilts a little, the centre of buoyancy shifts to the centre of the newly displaced water, and the vertical drawn through it cuts the original axis of the body at a point called the metacentre. If that point lies above the centre of gravity, the weight and the upthrust form a couple that turns the body back to its old position, so the equilibrium is stable; the gap between the two points is the metacentric height, and a larger value gives a stiffer, quicker roll. Option A is the opposite case: with the metacentre below the centre of gravity the same couple tips the body further over, which is unstable equilibrium, and if the two coincide the body is in neutral equilibrium. Options B and C are wrong because the metacentre's position relative to the centre of buoyancy decides nothing; only its position relative to the centre of gravity does. Exam tip: M above G is stable, M below G capsizes.

The correct answer is C, Oersted. In 1820 the Danish scientist Hans Christian Oersted saw that a compass needle kept near a wire swung aside the moment a current flowed through the wire, and swung the other way when the current was reversed. That small observation proved that an electric current sets up a magnetic field around itself, which is the magnetic effect of current, and it opened the whole study of electromagnetism. The CGS unit of magnetising field strength, the oersted, carries his name. Option A is wrong because James Clerk Maxwell came later and gathered the laws of electricity and magnetism into four equations, showing that light itself is an electromagnetic wave. Option B is wrong because John Ambrose Fleming only gave the left hand and right hand rules, which tell us the direction of the force or of an induced current. Option D is wrong because Michael Faraday discovered electromagnetic induction in 1831, the opposite effect. Exam tip: Oersted 1820, current makes magnetism; Faraday 1831, magnetism makes current.

The correct answer is D, Tunnel diode. A tunnel diode, also called an Esaki diode after Leo Esaki who made it in 1957, is heavily doped on both sides, so its depletion layer is extremely thin and electrons cross it by quantum tunnelling. Over part of its forward characteristic the current falls as the voltage rises, giving a negative resistance region, and it is this property that lets the diode both amplify a signal and sustain oscillations in a circuit. It switches extremely fast and is used in microwave oscillators and high frequency circuits. A is wrong because a point contact diode is used to detect and rectify high frequency signals. B is wrong because a Zener diode works in reverse breakdown and is used to regulate voltage. C is wrong because an ordinary junction diode only rectifies, allowing current one way. Exam tip: tunnel diode means negative resistance, so it can amplify and oscillate; Zener diode means voltage regulation.

The correct answer is B, Alkali metals. Potassium sits in group 1 of the periodic table along with lithium, sodium, rubidium, caesium and francium, and these six are called the alkali metals because their oxides and hydroxides dissolve in water to give strong alkalis. Each has a single electron in its outermost shell, which it loses easily, so they are soft, highly reactive metals that are stored under kerosene and react with water to release hydrogen. Potassium, symbol K from the Latin kalium, burns with a lilac flame. A is wrong because the alkaline earth metals are group 2, such as magnesium and calcium, with two outer electrons. C is wrong because noble gases like helium and argon are group 18 and are almost inert. D is wrong because halogens such as chlorine and iodine are group 17 non-metals. Exam tip: group 1 alkali metals, group 2 alkaline earth metals, group 17 halogens, group 18 noble gases.

The correct answer is B. In a double displacement reaction two compounds exchange their ions, so both reactants must be compounds. Here hydrogen and oxygen are elements combining to form a single product, water, which makes it a combination reaction and also a combustion and redox reaction, but certainly not a double displacement. Option A is wrong as a choice because barium chloride and sulphuric acid swap partners to give a white precipitate of barium sulphate and hydrochloric acid, the classic precipitation type of double displacement. Option C is wrong because copper sulphate and hydrogen sulphide exchange ions to give black copper sulphide and sulphuric acid. Option D is wrong because sodium hydroxide and hydrochloric acid exchange ions to give salt and water, which is neutralisation, a special case of double displacement. The test to apply is simple: look for two compounds exchanging partners.

The correct answer is B, orange. Citrus fruits such as orange, lemon, lime and grapefruit owe their sharp sour taste to citric acid, which is the acid textbooks name for this family and the one examiners expect here. Option A is wrong because tomato is listed with oxalic acid in the standard table, the same acid found in spinach. Option C is wrong because tamarind, like grapes, contains tartaric acid, which is also the acid mixed with baking soda to make baking powder. Option D is wrong because sour milk and curd contain lactic acid, produced when bacteria act on the sugar of milk. Learn the food and acid pairs as a single block, since one of them appears in almost every science paper: lemon and orange with citric acid, vinegar with acetic acid, apple with malic acid and ant sting with formic acid.

The correct answer is A, Sodium bicarbonate (Sodium hydrogen carbonate). Baking soda is sodium hydrogen carbonate, NaHCO3, a mild base made by the Solvay process from brine, ammonia and carbon dioxide. On heating, or on meeting an acid such as the tartaric acid in baking powder, it gives off carbon dioxide, and it is these bubbles that make bread and cake rise. The same reaction makes it useful in soda acid fire extinguishers and as an antacid, since it neutralises excess hydrochloric acid in the stomach. Option B is wrong because sodium carbonate, Na2CO3, is washing soda, a much stronger base used for cleaning and in glass making. Option C is wrong because potassium bicarbonate is a different salt, used in some fire extinguishers and fertilisers, not in the kitchen. Option D is wrong because potassium carbonate is potash, used in soap and glass. Exam tip: baking soda NaHCO3, washing soda Na2CO3.10H2O, caustic soda NaOH, and bleaching powder Ca(OCl)Cl.