General Science Mixed Quiz: Set 26

The correct answer is B, Michael Faraday. In 1831 Faraday showed that when the magnetic flux linked with a closed coil changes, whether by moving a magnet, moving the coil or changing the current in a nearby coil, a current is induced in it. This discovery is the basis of the generator, the transformer and almost the whole of electrical power engineering.

Option A, Oersted, made the complementary discovery eleven years earlier, in 1820, when he found that a compass needle is deflected near a current-carrying wire, showing that a current produces a magnetic field. Option C, Volta, invented the voltaic pile, the first electric battery, and the volt is named after him. Option D, James Watt, was an engineer of the steam engine and gave his name to the unit of power, but he had nothing to do with induction. The pair worth fixing in memory is Oersted in 1820 and Faraday in 1831.

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 B, atomic number. Henry Moseley showed in 1913, from the frequencies of the X-rays that elements emit, that the atomic number, the number of protons in the nucleus, is the more fundamental property of an element. The periodic law was therefore restated: the properties of elements are a periodic function of their atomic numbers. Option A is wrong because atomic mass was the basis of Mendeleev's law of 1869, which could not place isotopes and needed pairs such as cobalt and nickel to be put out of mass order. Option C is wrong because density is a physical property that shows no simple periodic pattern of this kind. Option D is wrong because valency follows from the electron arrangement and so is itself a consequence of the atomic number, not the basis of the law.

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, in the live wire. The fuse is a short piece of wire of low melting point placed in series in the live line, so that an excessive current melts it and breaks the circuit. Because the break is made on the live side, the appliance is left completely disconnected from the high potential and is safe to handle.

Option A is wrong because a fuse in the neutral wire would indeed stop the current, but the appliance would remain joined to the live wire and anyone touching it could still receive a shock. Option C is wrong because the earth wire is a safety path to the ground and must never carry a fuse, as breaking it would remove the very protection it provides. Option D is wrong because a fuse placed in parallel would short the appliance instead of protecting it; a fuse is always in series with the load it protects.

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, Thorium. John Newlands arranged the fifty-six elements known in 1866 in order of increasing atomic mass, beginning with hydrogen, the lightest, and ending with thorium, the fifty-sixth. He noticed that every eighth element had properties like the first, and named the pattern the Law of Octaves after the musical scale. The law failed once more elements were found, because there was no room left in the arrangement for them. Option A is wrong because radium was discovered only in 1898 by Marie and Pierre Curie, long after Newlands' table. Option C is wrong because iron lies in the middle of the arrangement, not at its end. Option D is wrong because rhodium too sits among the earlier elements and was not the last in his list.

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 B. The tangent drawn to a magnetic field line at any point gives the direction of the field at that point. If two lines crossed, two different tangents could be drawn at the point of crossing, which would mean the compass needle placed there would have to point in two directions at once. Since that is impossible, field lines never intersect.

Option A is wrong because the field being zero is a different situation, called a neutral point, where no line passes at all rather than two crossing. Option C is beside the point: field lines are indeed a way of picturing the field, but even as a picture they must show one direction at each point, so being imaginary is not the reason. Option D states a true fact, that a magnet always has both poles and a single pole cannot exist, but it explains why lines are closed curves and not why they cannot cross.

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 C, 7 periods and 18 groups. The modern periodic table has seven horizontal rows, called periods, and eighteen vertical columns, called groups. The first period holds only two elements, the second and third hold eight each, the fourth and fifth hold eighteen each and the sixth holds thirty-two, while the lanthanides and actinides are shown in two separate rows below. Option A is wrong because it reverses the two counts. Option B is wrong because eighteen is the number of groups, not of periods. Option D is wrong because eight groups belonged to Mendeleev's older table, which had eight vertical columns; the eighteen-group form came with the long form of the modern table, in which elements of a group share the same number of outermost electrons. A useful check is that seven is always the smaller of the two numbers, because the table is wider than it is tall.

The correct answer is B, Lungs. Pneumonia is an infection of the lungs in which the alveoli, the tiny air sacs where oxygen passes into the blood, fill with fluid or pus. That is why the patient has cough with phlegm, fever with chills, chest pain and difficulty in breathing, and the oxygen level in the blood can fall. It is caused most often by the bacterium Streptococcus pneumoniae, and also by other bacteria, viruses and fungi; it spreads through droplets, and children and the elderly are the worst affected. Vaccines against pneumococcus and influenza give protection. Option A is wrong because the kidney is affected by nephritis and kidney stones. Option C is wrong because the liver is affected by hepatitis, jaundice and cirrhosis. Option D is wrong because the heart is affected by conditions such as rheumatic heart disease and myocarditis. Exam tip: pneumonia and tuberculosis attack the lungs, hepatitis the liver, nephritis the kidney.

The correct answer is C, the kilowatt hour. It is the energy consumed by an appliance of one kilowatt working for one hour, and it equals three point six million joules. The electricity meter in a house counts these units, which is why the kilowatt hour is often called simply a unit of electricity.

Option A, the watt, is the SI unit of power, that is the rate of using energy, not of energy itself, so it cannot appear on a bill as a quantity consumed. Option B, the volt ampere, is also a unit of power, used for apparent power in alternating current work, and again measures a rate. Option D, the joule per second, is just another name for the watt and so has the same problem. Only the kilowatt hour multiplies power by time and therefore measures energy.

The correct answer is C, Thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. This is called complementary base pairing, and it is why one strand of DNA can be used to copy the other. The double-helix model was proposed by James Watson and Francis Crick in 1953, using X-ray images made by Rosalind Franklin. Adenine and guanine are purines with two rings, while thymine and cytosine are pyrimidines with one ring, so each pair has the same width and the helix stays even. In RNA, thymine is replaced by uracil. Option A is wrong because guanine is a purine like adenine and pairs with cytosine. Option B is wrong because cytosine pairs with guanine through three hydrogen bonds. Option D is wrong because histone is a protein around which DNA is wound in chromosomes; it is not a base at all. Exam tip: A pairs with T by two bonds, G with C by three; RNA has U in place of T.

The correct answer is A, atomic number but different mass number. Isotopes are atoms of the same element, so they have the same number of protons and therefore the same atomic number, but they carry different numbers of neutrons, which makes their mass numbers differ. Hydrogen has three isotopes, protium, deuterium and tritium, and chlorine occurs naturally as chlorine-35 and chlorine-37. Option B is wrong because atoms with the same mass number but different atomic numbers are isobars, such as argon-40 and calcium-40. Option C is wrong because atoms with the same number of neutrons but different numbers of protons are called isotones. Option D is wrong because atoms with the same number of protons and the same number of neutrons are simply identical atoms of one isotope, not isotopes of each other. Because isotopes differ only in neutrons, they share the same chemical behaviour and differ in physical properties such as density and radioactivity.

The correct answer is D, Galvanometer. A galvanometer detects whether a current is flowing in a circuit and shows its direction, because its needle moves to one side or the other about a central zero. It works on the turning effect of a magnetic field on a current carrying coil, and it is so sensitive that it responds to very small currents, which is why it is used to detect rather than to measure. The same instrument becomes an ammeter when a low resistance shunt is joined in parallel with it, and a voltmeter when a high resistance is joined in series. Option A is wrong because an ohmmeter measures resistance. Option B is wrong because a voltmeter measures potential difference and is connected in parallel across a component. Option C is wrong because a rheostat is a variable resistor used to change current, not to detect it. Exam tip: galvanometer detects, ammeter measures current in series, voltmeter measures voltage in parallel.

The correct answer is C. The resistance of a wire equals the resistivity of the material multiplied by the length and divided by the area of cross section. A longer wire gives the electrons a longer path and more collisions, so the resistance rises with length; a thicker wire gives them more room, so the resistance falls as the area grows.

Option A reverses the dependence on thickness, which is why a thin wire heats up more than a thick one carrying the same current. Option B reverses the dependence on length. Option D is wrong because only the resistivity, not the resistance, is independent of the size of the specimen; resistivity is a property of the material and changes only with the substance and its temperature. A useful check: doubling the length doubles the resistance, while doubling the diameter makes the area four times larger and cuts the resistance to a quarter.

The correct answer is B, J. J. Thomson. After discovering the electron in 1897, J. J. Thomson pictured the atom as a sphere of positive charge with negatively charged electrons stuck in it, a picture often compared to plums in a pudding or seeds in a watermelon. It explained why an atom is electrically neutral, but it had no nucleus and could not survive Rutherford's scattering experiment. Option A is wrong because John Dalton's 1808 theory treated the atom as indivisible and offered no internal structure at all. Option C is wrong because Rutherford replaced this model with the nuclear one after the gold foil experiment. Option D is wrong because Niels Bohr then added fixed permitted shells to Rutherford's nucleus in order to explain why the atom is stable.

The correct answer is C, 24 Joule. Work done in moving a charge through a potential difference is W = Q × V, so W = 2 × 12 = 24 joule. Potential difference between two points is defined as the work done per unit charge in carrying that charge from one point to the other, that is V = W/Q. Its unit, the volt, is therefore one joule per coulomb, and this work does not depend on the path taken between the two points. Moving 2 coulombs across 12 volts thus needs 24 joules of energy. A is wrong because 6 joule would be the work for only 0.5 coulomb at 12 V. B is wrong because 18 joule does not follow from any pairing of the given values. D is wrong because 12 joule is the work for 1 coulomb, not for 2 coulombs. Exam tip: remember V = W/Q, so W = QV, and 1 volt = 1 joule per coulomb.

The correct answer is C, Scandium, gallium and germanium. Mendeleev arranged the elements by increasing atomic mass in 1869 and left blank spaces where his pattern demanded an element that was not yet known. He described in advance the mass, density and compounds of three of them, calling them eka-boron, eka-aluminium and eka-silicon, and when scandium, gallium and germanium were discovered they matched his descriptions closely, which won the periodic law wide acceptance. Option A is wrong because sodium, potassium and calcium were all well known long before 1869. Option B is wrong because cobalt, nickel and copper were known too, and cobalt and nickel were in fact the pair he had to place out of strict mass order. Option D is wrong because radium, radon and rhenium were found much later and were not among his three predictions.