General Science Mixed Quiz: Set 19

The correct answer is B, minus 10 centimetres. By the sign convention the focal length of a concave lens is negative, so f is minus 15 centimetres, and the object distance measured against the direction of the incident light is minus 30 centimetres. Putting these in the lens formula 1/v minus 1/u equals 1/f gives 1/v equal to 1/f plus 1/u, that is minus 1/15 plus minus 1/30, which is minus 3/30 or minus 1/10. Hence v is minus 10 centimetres.

The negative sign shows that the image lies on the same side as the object, so it is virtual and erect, and being nearer the lens than the object it is also diminished. That is true of a concave lens for every position of the object. Options A, C and D come from dropping a sign or from adding the reciprocals wrongly.

The correct answer is A, Distillation. Distillation separates a liquid from a solution or from another liquid by boiling it and condensing the vapour, so it is used when the components differ in boiling point, as in getting pure water from salt water or separating acetone from water. It is not the method for purifying a solid mixed with solid impurities. Option B is useful because sublimation purifies a solid that turns straight into vapour on heating, such as camphor, naphthalene, iodine or ammonium chloride, leaving the non-volatile impurity behind. Option C is useful because crystallization dissolves the solid in a hot solvent and lets pure crystals form on cooling, the standard way to purify alum, copper sulphate and sugar. Option D is wrong because two of the three processes do purify solids, so they cannot all be useless. Exam tip: solids are purified by sublimation, crystallization and chromatography; distillation is for liquids.

The correct answer is C, Pitch. Pitch is the characteristic of a sound by which the brain judges it as shrill or flat, and it is decided by the frequency of the wave. A higher frequency is heard as a higher pitch, which is why a woman's voice or a whistle sounds shriller than a drum or a man's voice. The physical quantity is frequency; the sensation produced in the brain is pitch.

Option A, wavelength, is the distance between two successive compressions and is a measurement of the wave in space, not a sensation. Option B, wave velocity, depends on the medium and its temperature and is the same for a shrill and a flat sound in the same air. Option D, oscillation, simply means one complete to and fro vibration; counting oscillations per second gives frequency, but the word itself names no property that the brain interprets.

The correct answer is C, Arthropoda. The name itself says so: in Greek arthros means jointed and podos means foot, so arthropods are the animals with jointed legs. They also have a hard outer skeleton of chitin, a segmented body and an open circulatory system, and they shed the skeleton as they grow, a process called moulting. Arthropoda is the largest phylum in the animal kingdom, holding insects, spiders, scorpions, crabs, prawns, centipedes and millipedes - about eighty out of every hundred known animal species. Option A is wrong because molluscs such as snails, octopus and mussels have a soft body with a muscular foot and usually a shell. Option B is wrong because nematodes are unsegmented roundworms like Ascaris, with no legs at all. Option D is wrong because echinoderms such as starfish and sea urchins are spiny-skinned marine animals that move on tube feet. Exam tip: Arthropoda - jointed legs, chitin skeleton, largest phylum; Mollusca is the second largest.

The correct answer is C, Graphite. Among the allotropes of carbon, graphite has the lowest standard enthalpy of formation, which is taken as zero, so it is the reference state and the most stable form under ordinary conditions of temperature and pressure. In graphite each carbon atom is sp2 hybridised and bonded to three others in flat hexagonal sheets, and the loose sheets slide over one another, which makes it soft and a good lubricant; the spare electron in each atom makes graphite a conductor of electricity. Option A is wrong because coal is not a pure allotrope but an impure mixture of carbon with hydrogen, sulphur and mineral matter. Option B is wrong because fullerenes such as C60 are strained cage molecules and are less stable than graphite. Option D is wrong because diamond, though the hardest natural substance, is slightly higher in energy and turns to graphite very slowly. Exam tip: graphite most stable and conducts electricity, diamond hardest and does not.

The correct answer is D, uterus. The zygote divides as it travels down the fallopian tube and the resulting ball of cells gets implanted in the thick lining of the uterus.

Fertilisation itself takes place in the fallopian tube, where a sperm fuses with the ovum to form the zygote. Repeated division turns it into an embryo, which reaches the uterus in about a week and sinks into the endometrium, the soft inner wall prepared by hormones. There the placenta develops and supplies the growing embryo with food and oxygen from the mother's blood while carrying away waste. Human pregnancy lasts about nine months.

Option A is wrong because the cervix is only the narrow neck of the uterus that opens into the vagina. Option B is wrong because the ovary produces the ovum and hormones but does not hold the embryo. Option C is wrong because the vagina is the passage that receives the sperm and later serves as the birth canal.

Exam tip: fertilisation in the fallopian tube, implantation in the uterus, nourishment through the placenta.

The correct answer is D, green. Barium compounds such as barium nitrate give fireworks and signal flares a bright green flame.

The colour comes from a flame test. Heat excites the electrons of the metal ion, and as they fall back they release light of a fixed wavelength that is typical of that metal. Barium gives apple green, so barium nitrate is the standard green agent in pyrotechnics, where it also supplies oxygen to the burning mixture.

Option A is wrong because orange comes from calcium salts such as calcium chloride. Option B is wrong because blue is produced by copper compounds, notably copper chloride. Option C is wrong because yellow is the signature of sodium, which is why a sodium vapour lamp glows yellow.

Exam tip: remember the flame colours - sodium yellow, potassium lilac, calcium brick red, copper blue-green, barium apple green, strontium crimson.

The correct answer is D, Lead and tin. Solder is an alloy of lead and tin, usually in nearly equal parts.

An alloy is a mixture of a metal with one or more other elements, made to gain a property the pure metal lacks. Solder is useful because the mixture melts at a far lower temperature than either lead or tin alone, so it flows easily and is used to join wires and electrical joints. Other alloys asked in papers are brass, made of copper and zinc, bronze of copper and tin, stainless steel of iron, chromium and nickel, and German silver of copper, zinc and nickel.

Option A is wrong because lead with copper is not the soldering alloy. Option B is wrong because tin with iron gives tin plating, used for tin cans. Option C is wrong because lead and iron together are not used as solder.

Exam tip: solder is lead plus tin and melts at a low temperature; brass is copper and zinc, bronze is copper and tin.

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 D, Thallophyta. Algae belong to Thallophyta, the simplest division of the plant kingdom. Their body is a thallus, which means it is not divided into root, stem and leaf, and they have no vascular tissue. Most algae live in water, make their own food by photosynthesis and reproduce by spores; Spirogyra, Ulothrix, Chara and Volvox are common examples. Option A is wrong because angiosperms are flowering plants whose seeds lie enclosed in a fruit, the most advanced group of all. Option B is wrong because pteridophytes, such as ferns, are the first plants with proper vascular tissue, though they bear no seeds. Option C is wrong because bryophytes, such as mosses and Marchantia, are called the amphibians of the plant kingdom; they stand a step above thallophytes and need water for reproduction. Exam tip: the order of the plant kingdom is Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.

The correct answer is D, gold. Calaverite is gold telluride, with the formula AuTe2.

It is one of the very few minerals in which gold occurs chemically combined rather than as the free metal, because gold is a noble metal that usually resists reaction. Calaverite was named after Calaveras County in California, where it was found in 1861, and it is an important gold ore in Kalgoorlie in Australia and in Cripple Creek in Colorado. It looks brassy yellow to silvery white and is brittle.

Option A is wrong because the common silver telluride is hessite, and silver's chief ore is argentite. Option B is wrong as zinc is mined mainly as zinc blende, a sulphide. Option C is wrong because copper comes largely from copper pyrites, malachite and cuprite.

Exam tip: link ore to metal - calaverite gold, argentite silver, zinc blende zinc, bauxite aluminium, haematite iron, cinnabar mercury.

The correct answer is C, Breaking a chalk stick. Force has to be applied to break the chalk because its particles hold one another together, and that pull is the force of attraction between particles.

Every substance is made of particles that attract one another, and the strength of that attraction decides how hard a thing is to break. The attraction is strongest in solids, less in liquids and least in gases, which is why an iron rod needs a hammer, water can be separated with a finger and air offers no resistance at all. The school activity of breaking chalk, then a pencil and then an iron nail shows the difference in this force from one solid to another.

Option A is wrong because compressing a sponge only squeezes out the air in its pores. Option B is wrong because dissolving sugar shows diffusion and the spaces between particles. Option D is wrong because heating ice shows a change of state, not the attraction itself.

Exam tip: attraction between particles is strongest in solids, weaker in liquids and weakest in gases.

The correct answer is A, Ant. Among the four, the ant has the largest brain in proportion to its body. An ant’s brain is tiny in absolute terms, with about two hundred and fifty thousand neurons, yet it makes up roughly a sixth of the insect’s body weight, a share no vertebrate comes close to. This is a general rule of body size: as animals get smaller, the brain shrinks more slowly than the body, so small creatures carry proportionately bigger brains. Option B is wrong because an elephant has the largest brain in absolute weight on land, about five kilograms, but that is a very small fraction of a body of several tonnes. Option C is wrong because a dolphin, though highly intelligent, has a brain near one per cent of its body weight. Option D is wrong because a human brain is about 1.4 kilograms, roughly two per cent of body weight, high for a vertebrate but far below an ant’s share. Exam tip: elephant biggest brain by weight, ant biggest in proportion.

The correct answer is A, 2. A centre-tap full wave rectifier needs two p-n junction diodes, one for each half of the input cycle. The secondary winding of the transformer is tapped at its middle, so its two halves give equal voltages of opposite sign. During one half cycle the upper diode conducts and during the next half cycle the lower diode conducts, and both send current through the load in the same direction, so the output has two pulses in every cycle. That is why a full wave rectifier gives a higher average output and a lower ripple than a half wave one. The other way to build a full wave rectifier is the bridge circuit, which uses four diodes but needs no centre tap. Option B is wrong because one diode makes a half wave rectifier that uses only half of each cycle. Option C is wrong because four diodes are used in a bridge rectifier. Option D is wrong because six diodes are used in a three-phase full wave rectifier. Exam tip: half wave 1 diode, centre-tap full wave 2, bridge 4.

The correct answer is C, a and c, that is Spirulina and Chlorella. Both are tiny algae grown in tanks and sold as protein rich food supplements, and both have been studied as food for astronauts. Spirulina is a blue green alga, really a cyanobacterium, whose dried powder is about sixty per cent protein and also carries iron and beta carotene. Chlorella is a single celled green alga that multiplies very fast in a small space and gives off oxygen as it grows, which is why space agencies have tested it in closed life support systems. Such food from microbes is called single cell protein. Option A is wrong because Spirogyra, the slippery filamentous alga of ponds, is not eaten as a supplement. Option B is wrong for the same reason, as it also carries Spirogyra. Option D is wrong because it leaves out both correct names and adds Funaria, which is a moss and not an alga at all. Exam tip: Spirulina and Chlorella give single cell protein.

The correct answer is A, Archimedes' Principle. It states that the upthrust on a body dipped fully or partly in a fluid equals the weight of the fluid the body pushes aside. This is why a bucket of water feels lighter while it is still in the well, and why a ship of steel floats: its hollow shape displaces enough water to balance its own weight. The principle also gives the law of flotation and is used to find the purity of metals and the density of liquids with a hydrometer. B is wrong because Bernoulli's principle links the speed of a flowing fluid with its pressure, and explains lift on an aeroplane wing. C is wrong because the Beer–Lambert law deals with how much light a solution absorbs as it passes through. D is wrong because Pascal's law says pressure applied to an enclosed fluid is passed on equally in every direction, which is the basis of hydraulic brakes and lifts. Exam tip: Archimedes for buoyancy, Pascal for hydraulic press, Bernoulli for aerofoil lift.

The correct answer is C, Two. A normal umbilical cord contains two arteries and one vein, three blood vessels in all.

The umbilical cord joins the developing foetus to the placenta. The two umbilical arteries carry deoxygenated blood, carbon dioxide and wastes from the foetus to the placenta, while the single umbilical vein brings oxygen-rich blood and nutrients from the placenta back to the foetus. This is the reverse of the usual pattern in the body, where arteries carry oxygenated blood. The vessels are cushioned by a jelly-like tissue called Wharton's jelly, and a mature cord is about 50 to 55 cm long.

A is wrong: three is the total number of vessels, not of arteries. B is wrong: one is the number of umbilical veins. D is wrong: four vessels are never present in a normal cord.

Exam tip: Umbilical cord - two arteries plus one vein; the vein is the one carrying oxygenated blood to the foetus.

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 B, Papaver Somniferum. Opium is the dried latex of the opium poppy, whose botanical name is Papaver somniferum; the second word means sleep bringing. The milky latex is collected by making shallow cuts in the unripe capsule, and from it come the medicines morphine and codeine, used to control pain and cough. India grows the crop only under licence from the Narcotics Commissioner at Gwalior in Madhya Pradesh, and the licensed districts lie in Madhya Pradesh, Rajasthan and Uttar Pradesh, which is why state papers ask this question. Option A is wrong because Emblica officinalis is amla, the Indian gooseberry, rich in vitamin C. Option C is wrong because Rauvolfia serpentina is sarpagandha, the source of reserpine used for high blood pressure. Option D is wrong because Cinchona species yield quinine, the old treatment for malaria. Exam tip: opium Papaver somniferum, amla Emblica officinalis, quinine from Cinchona.

The correct answer is B, Gamma rays. Gamma rays sit at the far end of the electromagnetic spectrum, with the shortest wavelength and therefore the highest frequency and energy. Arranged from the longest wave to the shortest, the spectrum runs radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. All of them travel at the same speed in vacuum, so a shorter wave must have a higher frequency and each packet carries more energy. Gamma wavelengths are smaller than about 0.01 nanometre; they come out of the nucleus of a radioactive atom and are used to sterilise surgical instruments and to treat tumours. Option A is wrong because visible light measures roughly 400 to 700 nanometres, tens of thousands of times longer. Option C is wrong because infrared lies just beyond red and is longer than visible light, which is why we feel it as heat. Option D is wrong because X-rays are short but still longer than gamma rays, and they come from electrons, not the nucleus. Exam tip: the energy order is the reverse of the wavelength order.