General Science Mixed Quiz: Set 7

The correct answer is B, M L² T⁻². Work is force multiplied by displacement. Force has the dimensions M L T⁻², and multiplying it by a length adds one more power of L, which gives M L² T⁻². Energy has the same dimensions as work, since energy is the capacity to do work, and so does torque.

Option A, M L T⁻², is the dimensional formula of force, and also of weight, which is a force. Option C, M L² T⁻³, belongs to power, since power is work divided by time and therefore carries one extra power of T in the denominator. Option D, M L⁻¹ T⁻², is the formula for pressure, which is force divided by area. Because work and torque share the same dimensions, dimensional analysis alone cannot tell them apart, a standard limitation of the method.

The correct answer is B, Pyrometer. A pyrometer measures very high temperatures, such as those of furnaces, kilns and molten metal, without touching the hot object. It works on the principle that every hot body gives off thermal radiation whose intensity and colour depend on its temperature; the instrument reads this radiation and converts it into a temperature value. Ordinary mercury thermometers stop at about 350 degrees Celsius, so steel plants, glass works and cement kilns rely on pyrometers, which can read well above 1,000 degrees Celsius. The word comes from the Greek pyro, meaning fire. A is wrong because a bolometer measures the power of incident electromagnetic radiation, such as infrared or microwaves, not furnace temperature. C is wrong because an ammeter measures electric current in amperes. D is wrong because a fluxmeter measures magnetic flux. Exam tip: pyrometer for furnace heat, thermometer for body heat, ammeter for current, fluxmeter for magnetism.

The correct answer is D, New Cartesian sign convention. It is the standard set of rules used for reflection by spherical mirrors and for the mirror formula. Under this convention the pole of the mirror is the origin and the principal axis is the x-axis. The object is always placed on the left, all distances are measured from the pole, distances in the direction of the incident light are positive and those against it are negative. Heights above the axis are positive and below it negative, so a concave mirror has a negative focal length and a convex mirror a positive one. A is wrong because 'system convention' is not a named rule in optics. B is wrong because 'sign convention' is only the general idea; the specific set used is the New Cartesian one. C is wrong because 'mirror convention' is not a recognised term. Exam tip: New Cartesian means measure from the pole; concave f is negative, convex f is positive; mirror formula 1/v + 1/u = 1/f.

The correct answer is B, Baking soda. Its chemical name is sodium hydrogen carbonate and its formula is NaHCO3. It is a mild, non-corrosive base made by the Solvay process, in which brine is treated with ammonia and carbon dioxide. When heated it gives off carbon dioxide, which is why it makes cakes rise; it is also used in antacids, soda-acid fire extinguishers and as a cleaning agent. Note the trap in this question: baking soda and baking powder are different things. A is wrong because baking powder is a mixture of baking soda with a mild edible acid such as tartaric acid, not a single compound. C is wrong because washing soda is sodium carbonate decahydrate, Na2CO3.10H2O, used to soften hard water and in glass and soap making. D is wrong because plaster of Paris is calcium sulphate hemihydrate, CaSO4.1/2H2O, used for casts and moulds. Exam tip: baking soda NaHCO3, washing soda Na2CO3.10H2O, plaster of Paris CaSO4.1/2H2O, bleaching powder CaOCl2.

The correct answer is C, 143. The number 235 is the mass number and uranium's atomic number is 92, so the nucleus holds 235 minus 92, that is 143 neutrons. The mass number (A) counts protons and neutrons together, while the atomic number (Z) counts only protons, so neutrons = A − Z. Every uranium atom has 92 protons; its isotopes differ only in the number of neutrons. Uranium-235 makes up only about 0.7% of natural uranium, the rest being mostly U-238 with 146 neutrons. Yet U-235 is the isotope that splits easily when struck by a slow neutron, which is why reactor fuel is "enriched" in it. Option A is wrong because 235 is the total of protons and neutrons, not the neutrons alone. Option B is wrong because 92 is the number of protons, that is the atomic number. Option D is wrong because 51 has no link with this nucleus and is only a distractor. Exam tip: neutrons = mass number minus atomic number; U-235 has 143 and U-238 has 146.

The correct answer is D, Four. In diamond every carbon atom is joined to four other carbon atoms by strong covalent bonds. These bonds point towards the corners of a tetrahedron and build a rigid three-dimensional network that runs through the whole crystal. That network makes diamond the hardest natural substance, which is why it is used in cutting and drilling tools. Since all four valence electrons are used in bonding, no free electrons are left, so diamond does not conduct electricity. In graphite, the other common form of carbon, each atom bonds to only three others in flat hexagonal layers, and the spare electron lets graphite conduct. A is wrong because two bonds per carbon cannot build a solid network. B is wrong because carbon has a valency of four and cannot form five bonds. C is wrong because three bonds per atom describes graphite, not diamond. Exam tip: diamond = 4 bonds, hard, insulator; graphite = 3 bonds, soft, conductor.

The correct answer is B, Copper and Zinc. Brass is an alloy of copper and zinc, usually about 70 per cent copper and 30 per cent zinc. Adding zinc makes brass harder than pure copper, gives it a golden-yellow shine and helps it resist corrosion. That is why brass is used for utensils, door handles, taps, musical instruments like the trumpet, and cartridge cases. An alloy is a mixture of a metal with other metals or a non-metal, made to improve properties such as strength, hardness or resistance to rust. A is wrong because copper and tin make bronze, the alloy that gave its name to the Bronze Age. C is wrong because copper with aluminium gives aluminium bronze, not brass. D is wrong because copper and iron do not form a common alloy; iron with a little carbon makes steel. Exam tip: Brass = Cu + Zn, Bronze = Cu + Sn, Solder = Pb + Sn, Stainless steel = Fe + Cr + Ni + C, German silver = Cu + Zn + Ni.

The correct answer is B, Both I and II. Both pairs are wrong. Amyloplasts store starch, a carbohydrate, and aleuroplasts store proteins; oils and fats are stored by elaioplasts. Plastids are organelles found only in plant cells. Chloroplasts hold chlorophyll and do photosynthesis, chromoplasts hold the yellow, orange and red pigments of flowers and fruits, and leucoplasts are colourless storage plastids. The leucoplasts are named after what they keep: amyloplasts keep starch (amylum), as in potato tubers; elaioplasts keep oils (elaion means oil), as in castor seeds; aleuroplasts keep proteins (aleurone), as in the outer layer of wheat grains. A is wrong because it accepts pair II, which links aleuroplasts to carbohydrates instead of proteins. C is wrong because it treats both pairs as correct. D is wrong because it accepts pair I, which links amyloplasts to fats instead of starch. Exam tip: amylo = starch, elaio = oil, aleuro = protein; all three are leucoplasts.

The correct answer is C, Rickets. Vitamin D helps the intestine absorb calcium and phosphorus, so without it the bones of a growing child stay soft and bend, giving bow legs, a pigeon chest and a large forehead; this disease is rickets. In adults the same deficiency causes osteomalacia, a softening of already formed bones. Vitamin D is called the sunshine vitamin because the skin makes it when sunlight falls on it; fish liver oil, egg yolk and milk are food sources. Its chemical name is calciferol. A, Beriberi, is caused by lack of vitamin B1 (thiamine) and affects the nerves and the heart. B, Scurvy, comes from lack of vitamin C (ascorbic acid) and causes bleeding gums. D, Pneumonia, is an infection of the lungs caused by bacteria or viruses, not a deficiency disease. Exam tip: remember the pairs, A night blindness, B1 beriberi, C scurvy, D rickets, K delayed clotting.

The correct answer is C, more than the atmospheric pressure. Air always moves from a region of higher pressure to one of lower pressure, so it flows out of the lungs only when the pressure inside them rises above that of the outside air. During expiration the diaphragm relaxes and moves up into its dome shape, and the intercostal muscles between the ribs relax, so the ribs move down and inward. This reduces the volume of the chest cavity, which raises the pressure in the lungs and pushes the air out. Inspiration is the reverse: the diaphragm contracts and flattens, the chest cavity grows, lung pressure falls below atmospheric pressure and air rushes in. Option A is wrong because when the pressures are equal no air moves; this happens for a moment between breaths. Option B is wrong because lower pressure inside the lungs draws air in, which is inspiration. Option D is wrong because contraction of the diaphragm enlarges the chest and causes inspiration, not expiration. Exam tip: inspiration means the diaphragm contracts and lung pressure falls; expiration means it relaxes and lung pressure rises.

The correct answer is A, Aedes - Chikungunya - Bacteria. This set is wrong because chikungunya is caused by a virus, the chikungunya virus, and not by bacteria. It is spread by Aedes mosquitoes, the same day-biting mosquitoes that carry dengue and Zika, and it causes high fever with severe joint pain. The name comes from a word in the Makonde language of East Africa meaning 'that which bends up', describing patients bent over with pain. Aedes breeds in clean water stored in coolers, tyres, pots and tanks, which is why dengue and chikungunya cases rise after the monsoon. Option B is a correct set because the Culex mosquito spreads lymphatic filariasis, or elephantiasis, caused by parasitic worms such as Wuchereria bancrofti. Option C is correct because the female Anopheles mosquito spreads malaria, caused by the Plasmodium parasite, a protozoan. Option D is correct because Aedes also spreads dengue, which is caused by the dengue virus. Exam tip: Aedes carries dengue, chikungunya and Zika, all viruses; Anopheles carries malaria; Culex carries filariasis and Japanese encephalitis.

The correct answer is A, Melatonin. The pineal gland, a small pine-cone-shaped gland deep in the brain, secretes melatonin. Melatonin controls the body's day-night rhythm, called the circadian rhythm, and helps regulate sleep. The gland releases more melatonin in darkness and less in bright light, which is why bright screens late at night can disturb sleep. Melatonin also plays a part in the timing of puberty and in seasonal changes in some animals. The French philosopher Descartes once called the pineal gland 'the seat of the soul'. B is wrong because progesterone is made mainly by the ovaries (the corpus luteum) and helps prepare for and maintain pregnancy. C is wrong because epinephrine, or adrenaline, is released by the adrenal medulla and prepares the body for 'fight or flight'. D is wrong because insulin is made by the beta cells of the islets of Langerhans in the pancreas and lowers blood sugar. Exam tip: pineal gland, melatonin, sleep; pancreas, insulin; adrenal medulla, adrenaline.

The correct answer is A, Zinc, Iron, Manganese. All three are needed by plants only in very small amounts, which makes them micronutrients. Plants need macronutrients in large amounts: nitrogen, phosphorus and potassium as primary nutrients, and calcium, magnesium and sulphur as secondary ones. Micronutrients such as iron, manganese, zinc, copper, boron, molybdenum and chlorine are needed only in traces, yet a shortage of any one of them still harms the plant. For example, a lack of zinc causes khaira disease in rice, and a lack of iron makes young leaves turn yellow. B is wrong because potassium and magnesium are macronutrients, even though copper is a micronutrient. C is wrong because phosphorus and calcium are macronutrients. D is wrong because sulphur is a macronutrient and aluminium is not an essential plant nutrient at all. Exam tip: macro, nitrogen, phosphorus, potassium, calcium, magnesium and sulphur; micro, iron, manganese, zinc, copper, boron, molybdenum and chlorine.

The correct answer is A, The pressure in blood vessels exceeds outside pressure. At great heights the air is thin, so the atmospheric pressure acting on the body is much lower than at sea level. The blood inside our vessels keeps pushing outwards at nearly its usual pressure. In the nose the blood vessels are very fine and lie close to the surface, so when the pressure inside them becomes greater than the pressure outside, some of them burst and the nose bleeds. The cold, dry mountain air also makes the lining of the nose crack more easily. The same fall in air pressure is why water boils below 100 °C on mountains and food takes longer to cook. B is wrong because the pressure inside the vessels becomes more than, not less than, the outside pressure. C is wrong because equal pressures would give no push to burst the vessels. D is wrong because blood does not become thick enough at a height to cause nose bleeding. Exam tip: higher altitude, lower air pressure, so the pressure in blood vessels is relatively higher and the nose can bleed.

The correct answer is D, General theory of relativity. LIGO, the Laser Interferometer Gravitational-Wave Observatory in the USA, detected gravitational waves for the first time in September 2015 (announced in February 2016), and such waves were predicted by Einstein's general theory of relativity in 1916. General relativity treats gravity as the curving of space-time and says that huge accelerating masses, like two black holes spiralling into each other, send ripples through space-time at the speed of light. LIGO's two detectors at Hanford and Livingston measured a change in arm length smaller than the width of a proton. India is building a third detector, LIGO-India, at Hingoli in Maharashtra. A, String theory, has made no prediction that any experiment has yet confirmed. B, Special relativity, deals with motion at constant speed and does not include gravity. C, Quantum mechanics, describes atoms and particles, not gravitational waves. Exam tip: LIGO means gravitational waves, which means general relativity; the 2017 Physics Nobel went to Weiss, Barish and Thorne for it.

The correct answer is C, 277. Water is densest at about 4 degrees Celsius, and 4 plus 273 gives roughly 277 kelvin. Most liquids keep shrinking as they cool, but water behaves oddly: below 4 degrees Celsius it starts to expand again because its molecules begin forming the open, hexagonal pattern of ice. This anomalous expansion is why ice is lighter than water and floats, and why a lake freezes from the top while the 4-degree water sinks to the bottom, letting fish survive the winter. Its density at that point is very close to 1 gram per cubic centimetre. D is wrong because 273 kelvin is 0 degrees Celsius, the freezing point, where water is already less dense than at 4 degrees. A is wrong because 0 kelvin is absolute zero, where no liquid water can exist. B is wrong because 227 kelvin is about minus 46 degrees Celsius, far below freezing. Exam tip: maximum density of water at 4 degrees Celsius equals 277 K; freezing at 273 K, boiling at 373 K.

The correct answer is B, A bottle opener. Levers are grouped by where the fulcrum, the load and the effort sit. In a second class lever the load lies between the fulcrum and the effort. In a bottle opener the rim of the cap is the fulcrum at the tip, the cap being lifted is the load in the middle, and your hand applies the effort at the far end. Such levers always multiply force because the effort arm is longer; a wheelbarrow and a nutcracker work the same way. A, A pair of scissors, is a first class lever, with the pivot between the effort and the load. C, A cricket bat, is a third class lever: the lower hand applies the effort between the top hand, which acts as the fulcrum, and the ball. D, A bow and arrow, works by storing energy in the bent bow like a spring, not by placing the load between the fulcrum and the effort. Exam tip: first class has the fulcrum in the middle, second class the load in the middle, third class the effort in the middle.

The correct answer is B, barometer. A barometer measures the pressure of the atmosphere, traditionally by balancing it against a column of mercury. It is also used for forecasting weather, because a sudden drop in pressure signals an approaching storm, and for finding altitude, since pressure falls as one rises.

Option A, the hygrometer, measures the humidity of the air. Option C, the anemometer, measures the speed of the wind and is the cup-shaped device seen at weather stations. Option D, the lactometer, checks whether milk has been diluted, by measuring its relative density. Keep the confusing pair apart: hygrometer for humidity and hydrometer for the density of a liquid. The mercury barometer was invented by Evangelista Torricelli, and the aneroid barometer, which uses a sealed metal box instead of a liquid, is the portable form carried on aircraft and used as an altimeter. Pressure itself is measured in pascals, and one atmosphere is about 1.013 lakh pascals.

The correct answer is A, Red light has a longer wavelength and is scattered the least, making it visible from a distance. Red has the longest wavelength in visible light, about 700 nm, so the tiny particles of air, fog, smoke and dust scatter it the least. The light therefore travels far without fading and can be seen from a distance, which is exactly what a danger signal needs. This follows Rayleigh scattering: the shorter the wavelength, the more the light is scattered. The same idea explains why the clear sky looks blue, since blue light is scattered the most, and why the sun looks red at sunrise and sunset. B is wrong because red light is not more reflective than other colours. C is wrong because how easily a colour is produced has nothing to do with its use in signals. D is wrong because looks are not the scientific reason. Exam tip: longest wavelength = least scattering = red for danger; shortest wavelength = most scattering = blue sky.

The correct answer is D, 32. The N shell is the fourth shell (n = 4), and the most electrons a shell can hold is given by the formula 2n², so 2 × 4² = 32. The shells around the nucleus are named K, L, M and N for n = 1, 2, 3 and 4, and the same formula gives them room for 2, 8, 18 and 32 electrons. This is the Bohr–Bury scheme taught in Class 9. One more rule is often tested with it: the outermost shell of an atom cannot hold more than 8 electrons, which is why potassium is written 2, 8, 8, 1 and not 2, 8, 9. A is wrong because 2 is the capacity of the K shell. B is wrong because 8 is the capacity of the L shell. C is wrong because 16 is not the capacity of any shell; the M shell holds 18. Exam tip: remember 2n², so K = 2, L = 8, M = 18 and N = 32.