General Science Mixed Quiz: Set 32

The correct answer is B, dyne-sec/cm². The poise is the CGS unit of dynamic or absolute viscosity, named after the French physician Jean Poiseuille, and one poise equals one dyne-second per square centimetre, which is the same as one gram per centimetre per second. Dynamic viscosity measures the internal friction of a fluid, the shearing stress needed for a unit rate of shear, so its unit is a stress multiplied by time. In SI the unit is the pascal-second, and one poise equals 0.1 pascal-second. Water at room temperature has a viscosity of about one centipoise, while honey is thousands of times thicker. A is wrong because dyne/cm² is a unit of stress or pressure, with no time in it. C is wrong because gram is a unit of mass, and g-sec/cm² does not reduce to the dimensions of viscosity. D is wrong because gm-cm/sec² is the dyne itself, a unit of force. Exam tip: 1 poise = 1 dyne-s/cm² = 0.1 Pa-s; water is about 1 centipoise.

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, Gravitational force and Normal force. A block lying quietly on a table is in equilibrium, so the forces on it must add up to zero, but that does not mean there are no forces at all. The Earth pulls the block down with its weight, mg. The table pushes back on it with an equal and opposite normal reaction, acting perpendicular to the surface, and these two balance each other. Friction is a force that appears only when there is motion along the surface or a tendency towards such motion; nothing is pushing the block sideways here, so no friction acts. This is Newton's first law in a familiar everyday form. Option A is wrong because gravity alone would make the block accelerate downward through the table. Option C is wrong because static friction needs an applied horizontal force that the block is resisting. Option D is wrong because sliding friction acts only while a body is actually sliding over a surface. Exam tip: on a body at rest with no horizontal push, only weight and normal reaction act, and friction is zero.

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, 315 W. Power is the work done divided by the time taken, and here the work is the potential energy the boy gains while climbing the staircase. The total height is 45 steps multiplied by 14 cm, which is 630 cm or 6.3 m. The work done against gravity is W = mgh = 50 into 10 into 6.3 = 3150 joules. Dividing by the 10 seconds he takes gives P = 3150 divided by 10 = 315 watts. The watt is the SI unit of power and equals one joule per second. Option A is wrong because 315 is the right number but ms is a unit of time, not of power. Option C is wrong because 337.5 W follows from using a height other than 6.3 m. Option D is wrong because the joule measures work or energy rather than power, and 310.55 does not follow from the data. Exam tip: use P = mgh divided by t, and convert centimetres to metres before substituting.

The correct answer is B, Cones. Cones are the photoreceptor cells of the retina that respond to colour in bright light. The human retina carries two kinds of photoreceptors. Cones number about six to seven million, sit densely near the centre of the retina and come in three types, sensitive to red, green and blue light; the brain mixes their signals into every shade we see. They work only when the light is good, which is why colours fade at dusk. Option A is wrong because rods are far more numerous but work in dim light and give only shades of grey, not colour. Option C is wrong because the blind spot is the point where the optic nerve leaves the eyeball and carries no photoreceptors at all. Option D is wrong because the fovea is a small pit in the retina, a place rather than a cell type, although it is packed with cones. Exam tip: rods for night and grey, cones for colour and daylight; colour blindness is a defect of the cones.

The correct answer is D, It is upright and smaller than the object. A concave lens is a diverging lens, so for every position of a real object it forms an image that is virtual, erect and diminished. Rays that pass through a concave lens spread out; when they are extended backwards they appear to meet on the same side as the object, between the optical centre and the focus. Such an image cannot be caught on a screen. Because the image is always small and the field of view is wide, a concave lens is used in spectacles for myopia and in the peephole viewer of a door. A and B are wrong because an inverted image is always a real image, and a concave lens never forms one. C is wrong because a concave lens cannot magnify; an erect and enlarged image comes from a convex lens when the object lies between its optical centre and focus. Exam tip: concave lens – virtual, erect and diminished image, always.

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 D, Acoustics. Acoustics is the branch of physics that deals with how sound is produced, how it travels and how it is heard or absorbed. The word comes from a Greek root meaning to hear. Sound is a mechanical wave, so it needs a material medium and cannot pass through a vacuum; it travels at about 343 metres per second in air at room temperature and much faster in water and in steel. Acoustics is put to work in designing halls and studios so that echo and noise are controlled, and in sonar, ultrasound scanning and hearing aids. A is wrong because optics is the study of light, its reflection, refraction and the working of lenses and mirrors. B is wrong because photonics deals with the making, control and detection of photons, as in lasers and optical fibres. C is wrong because astrophysics studies the physics of stars, galaxies and the universe. Exam tip: acoustics – sound; optics – light; photonics – photons; seismology – earthquake waves.

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, 12.5 kWh. Electrical energy is power multiplied by time, so the unit follows directly from the units you put in. The oven is rated 2500 W, which is 2500 divided by 1000, that is 2.5 kilowatts. Running it for 5 hours uses E = P into t = 2.5 kW into 5 h = 12.5 kilowatt-hours. The kilowatt-hour is the commercial unit of electrical energy, the unit printed on a domestic electricity bill, and one kilowatt-hour equals 3.6 million joules. Option A is wrong because 12500 comes from forgetting to convert watts into kilowatts, so the figure is a thousand times too large. Option C is wrong because 12500 J would be the energy used in only 5 seconds, and a meter does not bill in joules. Option D is wrong because the number is right but the joule is the wrong unit here. Exam tip: one kilowatt-hour equals 1000 W into 1 h, or 3.6 million joules, so convert watts to kilowatts before multiplying by hours.

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 A, Isotopes of Hydrogen. Hydrogen has three isotopes: protium with one proton and no neutron, deuterium with one proton and one neutron, and tritium with one proton and two neutrons. All three have atomic number 1, so they occupy the same place in the periodic table, but their mass numbers are 1, 2 and 3. Deuterium forms heavy water, used as a moderator in nuclear reactors, while tritium is radioactive and is used with deuterium in fusion research. Hydrogen is the only element whose isotopes are given separate names of their own. B is wrong because carbon's isotopes are written as carbon-12, carbon-13 and carbon-14. C is wrong because uranium's main isotopes are uranium-235 and uranium-238. D is wrong because titanium's isotopes carry no special names of this kind. Exam tip: protium, deuterium and tritium all have atomic number 1 and mass numbers 1, 2 and 3.

The correct answer is B, Roasting. Roasting means heating a sulphide ore strongly in plenty of air, so that the sulphide turns into an oxide and the sulphur escapes as sulphur dioxide gas. The standard example is zinc blende: 2ZnS + 3O2 gives 2ZnO + 2SO2. An oxide is easier to reduce to the metal with carbon, which is why ores of zinc, lead and copper first pass through this step. Remember the key contrast: roasting uses excess air and suits sulphide ores, while calcination uses limited or no air and suits carbonate ores. A is wrong, because calcination heats carbonate ores such as calamine in limited air, as when ZnCO3 gives ZnO and CO2. C is wrong, because smelting is the later step in which the oxide is reduced to metal in a furnace with a reducing agent and a flux. D is wrong, because incineration is burning waste at a high temperature, not a step in extracting metals. Exam tip: sulphide ore, roasting, excess air; carbonate ore, calcination, little or no air.

The correct answer is C, zinc. Calamine is zinc carbonate, and since it is a carbonate ore it is converted to the oxide by calcination, that is by heating in the absence of air, before being reduced to the metal. The other important ore of zinc is zinc blende, which is the sulphide and is roasted rather than calcined. Option A is wrong because the chief ore of tin is cassiterite, the oxide. Option B is wrong because magnesium is obtained from magnesite, dolomite and from sea water as its chloride. Option D is wrong because copper comes mainly from copper pyrites, also called chalcopyrite, and from cuprite. A pair of definitions is worth keeping ready for this topic: calcination is heating a carbonate ore without air, while roasting is heating a sulphide ore in air, and both give the oxide.

The correct answer is A, Protein. The lens of the eye is made mostly of water and special proteins called crystallins, packed in a very regular order that keeps the lens clear so light can pass straight through to the retina. With age, and faster with diabetes, ultraviolet light, smoking or an injury, these proteins break down and clump together. The clumps scatter light, so the lens turns cloudy and vision becomes blurred, dim and glary. This clouding is a cataract, and it is one of the leading causes of blindness in India. It is treated by a short operation in which the cloudy lens is removed and replaced by an artificial intraocular lens. Option B is wrong because carbohydrate changes are not what clouds the lens, although high blood sugar in diabetes speeds up the protein damage. Option C is wrong because fat does not form the clear structure of the lens. Option D is wrong because the tear glands keep the eye moist and have nothing to do with the lens. Exam tip: cataract = cloudy lens from clumped proteins; glaucoma = raised pressure inside the eye.

The correct answer is D, propane and butane. Liquefied petroleum gas is a mixture of these two saturated hydrocarbons, which are gases at ordinary pressure but turn liquid under moderate pressure, so a large quantity of fuel fits into a small cylinder; a strong-smelling compound is added so that a leak is noticed. Option A is wrong because ethene is an unsaturated gas used to make polythene and to ripen fruit, not as cooking fuel. Option B is wrong because ethyne, also called acetylene, is burnt with oxygen in welding torches for its very hot flame, and it is not supplied in domestic cylinders. Option C is wrong because propene is a raw material of the plastics industry, chiefly for polypropylene. Remember also that compressed natural gas, used in vehicles, is mainly methane, a different fuel from LPG.

The correct answer is B, Ovum. The female egg cell, or ovum, is the largest cell in the human body. It measures about 100 to 130 micrometres across, roughly the thickness of a hair, and is the only human cell that can just be seen without a microscope. It is this big because it carries the cytoplasm, food store and machinery an embryo needs in its first days, and a girl is born with her whole stock of these cells already formed. A is wrong because the sperm is the smallest human cell, a few micrometres in the head, built only to swim and carry a nucleus. C is wrong because a nerve cell is the longest cell, since a single axon can run about a metre from the spinal cord to the toe, but it is extremely thin and not the largest in volume. D is wrong because an osteoclast, the cell that dissolves bone, is large and has many nuclei yet stays smaller than the ovum. Exam tip: ovum is the largest cell, sperm the smallest and the nerve cell the longest.

The correct answer is C, Carbohydrates. The buccal cavity is the mouth, and the saliva poured into it begins the digestion of starch, a carbohydrate. Three pairs of salivary glands supply saliva, which carries the enzyme salivary amylase, also called ptyalin. It works best in a slightly alkaline medium and breaks the long starch chains into the sugar maltose, which is why a piece of bread kept in the mouth slowly tastes sweet. The teeth and tongue help by grinding the food and rolling it into a bolus. A is wrong because protein digestion begins in the stomach, where pepsin works in the acid of hydrochloric acid. B is wrong because the digestion of fat takes place chiefly in the small intestine, where bile from the liver breaks fat into small droplets and pancreatic lipase acts on them. D is wrong because starch digestion clearly does begin in the mouth. Exam tip: mouth – starch by amylase; stomach – protein by pepsin; small intestine – fat by bile and lipase.

The correct answer is B, Villi. Villi are the small finger-like folds on the inner wall of the small intestine, so they belong to the digestive system. Their work is to enlarge the surface through which digested food is absorbed; each villus does hold a capillary and a lymph vessel inside it, but the villus itself is not a part of the circulatory system. The human circulatory system is made of the heart, the blood and the blood vessels. A is wrong because capillaries are the thinnest vessels, where gases and nutrients pass between blood and the tissues. C is wrong because veins carry blood back to the heart and have valves to stop it flowing backwards. D is wrong because arteries carry blood away from the heart and have thick elastic walls to take the pressure. Exam tip: villi absorb digested food in the small intestine; the heart, blood and blood vessels make up the circulatory system.