General Science Mixed Quiz: Set 18

The correct answer is A, Decrease in potential energy. A conservative force is one whose work depends only on the starting and the finishing point, not on the path taken, and whose work around any closed path is zero. Gravity and the spring force are the common examples. Potential energy is defined for such a force by the relation that the work it does equals the loss in potential energy. When a stone falls, gravity does positive work and the stone’s potential energy falls by exactly that amount. Option C is wrong because it states the opposite; potential energy rises only when work is done against the force, as in lifting the stone. Option B is right only when the conservative force is the sole force acting, so it is not the defining statement, and friction or an applied force would break it. Option D is wrong because kinetic energy grows, not falls, when such work is positive. Exam tip: conservative force, work equals minus the change in potential energy, and zero on a closed loop.

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 B, it slows down and bends towards the normal. A denser medium has a higher refractive index, and the refractive index is the speed of light in vacuum divided by its speed in the medium, so light must travel more slowly inside it. When the ray meets the surface at an angle, the part of the wavefront that enters first is slowed first, which swings the ray towards the normal. Air to glass and air to water are the standard examples.

Option A takes the correct change of speed with the wrong bending. Option C describes what happens in the opposite case, when light passes from a denser medium to a rarer one. Option D combines two errors at once. A ray that falls along the normal is a special case and passes straight through without bending, though its speed still changes.

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 B, 600 m. The speed of a wave is the product of its frequency and its wavelength, so the speed here is 50 hertz multiplied by 4 metres, that is 200 metres per second. Distance is speed multiplied by time, so in 3 seconds the wave covers 200 multiplied by 3, which is 600 metres. Always find the speed first and only then apply the time.

Option A, 100 m, would follow from dividing rather than multiplying somewhere in the working. Option C, 200 m, is the distance covered in one second and is the answer to a different question; it is the speed, not the answer asked for. Option D, 300 m, corresponds to no correct step at all and is included because it resembles the rounded speed of sound in air, which is irrelevant here since the speed is given indirectly by the data.

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 B, D.C. only. In a permanent magnet moving coil instrument the coil is pivoted in the field of a permanent magnet, so the deflecting torque is proportional to the current itself and not to its square. If alternating current is passed, the torque reverses every half cycle; the pointer cannot follow fifty reversals a second and rests at zero, because the average value of a sine wave over a full cycle is zero. That is why such an ammeter or voltmeter reads direct current only, and why a rectifier is placed ahead of it when alternating current has to be measured. Its scale is uniform and it draws very little power, which makes it the moving coil galvanometer of the laboratory. Options A and D are wrong for the reason just given. Option C is wrong because an impulse lasts a few microseconds, far too short for the inertia of a pivoted coil and pointer. Exam tip: moving coil reads D.C., moving iron reads both A.C. and D.C.

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 A, carbon dioxide. Urea is made industrially by reacting ammonia with carbon dioxide under high pressure.

The process runs in two steps: ammonia and carbon dioxide first form ammonium carbamate, which then loses a water molecule to give urea. Its formula is CO(NH2)2 and it carries about 46 per cent nitrogen, the highest of the common solid fertilisers, which is why it is the most used nitrogenous fertiliser in India. The ammonia itself comes from the Haber-Bosch process. Urea also has a place in the history of chemistry as the first organic compound synthesised in a laboratory, by Friedrich Wohler in 1828.

B is wrong: ammonia is itself made from nitrogen and hydrogen, and adding hydrogen gives no urea. C is wrong: ammonia with oxygen gives nitric oxide, a step towards nitric acid. D is wrong: ammonia with sulphuric acid gives ammonium sulphate, a different fertiliser.

Exam tip: Urea - ammonia plus carbon dioxide, formula CO(NH2)2, about 46 per cent nitrogen.

The correct answer is A, Liquid. At normal atmospheric pressure water stays liquid between 0 °C and 100 °C, and 12 °C lies inside that range. Water freezes into ice at 0 °C, which is its melting point, and boils into steam at 100 °C, which is its boiling point, when the pressure is one atmosphere. Between these two fixed points the molecules have enough energy to slide over one another but not enough to fly apart, so water flows and takes the shape of its container while keeping a fixed volume. Water does evaporate slowly at 12 °C from an open surface, but that happens only at the top layer and does not change the state of the water below. Option B is wrong because ionic is not a state of matter at all; it describes a kind of bond or compound. Option C is wrong because water becomes a gas, that is steam, only above 100 °C. Option D is wrong because water turns solid only at or below 0 °C. Exam tip: remember 0 °C and 100 °C as the fixed points of water at one atmosphere.

The correct answer is C. Lead and mercury are in fact the poorest conductors of heat among the metals, so calling them the best is wrong.

Metals conduct heat and electricity because of the free electrons that move through their lattice. Silver is the best conductor of heat, followed by copper, which is why cooking vessels and heat sinks are made of copper and aluminium. Lead and mercury conduct so weakly that they are the usual textbook example of poor metallic conductors.

Option A is a correct statement: most metals melt at high temperatures, tungsten at about 3400 degrees Celsius, though gallium and caesium are exceptions. Option B is correct, since good thermal conduction is a defining property of metals. Option D is correct too, as a fresh metal surface has lustre and is polished for that reason, while tarnishing is due to a layer of oxide.

Exam tip: best conductors silver then copper; poorest among metals lead and mercury.

The correct answer is D, 0.7 V. A silicon diode in forward bias drops about 0.7 volt across itself, whatever the supply voltage is. This value is the barrier or knee voltage of a silicon p-n junction: current begins to flow only after the applied voltage crosses about 0.7 V, and after that the drop across the diode stays near 0.7 V while the rest of the supply appears across the resistor. Here 12 V minus 0.7 V, that is 11.3 V, falls across the 240 ohm resistor and fixes the current in the circuit. A germanium diode has a lower knee voltage of about 0.3 V. Option A is wrong because 1.5 V is the voltage of a dry cell and has nothing to do with the junction. Option B is wrong because half the supply would appear across the diode only if it behaved like a resistor of the same value. Option C is wrong because the full 12 V appears across the diode only when it is reverse biased or the circuit is broken. Exam tip: silicon 0.7 V, germanium 0.3 V.

The correct answer is A, Ethanol. CH3CH2OH, also written C2H5OH, is ethanol or ethyl alcohol, the second member of the alcohol family. The -OH group attached to the carbon chain is the functional group that makes it an alcohol. Ethanol is a colourless liquid that boils at about 78 degrees Celsius, mixes with water in every proportion, and is used in alcoholic drinks, as a solvent in medicines and in ethanol-blended petrol. Alcohol free of water is called absolute alcohol, while alcohol made unfit for drinking by adding methanol and a dye is called denatured spirit. Option B is wrong because acetic acid, the acid in vinegar, is CH3COOH and carries the -COOH group. Option C is wrong because chloroform is CHCl3, once used as an anaesthetic. Option D is wrong because methane is CH4, the simplest hydrocarbon and the main part of natural gas. Exam tip: -OH means an alcohol and -COOH means a carboxylic acid.

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 A, The acid present in tomato - Formic acid. This pair is wrong, because tomato contains oxalic acid, along with some citric and malic acid.

Formic acid, or methanoic acid, is the acid of an ant sting and a bee sting, and its name comes from the Latin word for ant. Oxalic acid is found in tomato, spinach and other leafy vegetables. Learning the natural acids as pairs is the quickest way to handle such questions: lemon and orange give citric acid, curd gives lactic acid, vinegar gives acetic acid, apple gives malic acid and tamarind gives tartaric acid.

B is a correct match, so it is not the answer: orange does contain citric acid. C is correct as well, because grapes and tamarind contain tartaric acid. D is also correct, since rancid butter smells the way it does because of butyric acid.

Exam tip: Tomato - oxalic acid; ant sting - formic acid; do not mix the two.

The correct answer is B, Quantum Computing. A qubit, short for quantum bit, is the basic unit of information in a quantum computer. An ordinary bit can be only 0 or 1, but a qubit can exist in a superposition of 0 and 1 at the same time, and qubits can be entangled, so that the state of one is linked to another. Because of this, a set of qubits can explore many possibilities together, which could let quantum computers solve certain problems, such as simulating molecules or breaking some kinds of encryption, far faster than classical machines. Qubits are built from superconducting circuits, trapped ions or photons, and most must be kept close to absolute zero. India supports this field through its National Quantum Mission, approved in 2023. Option A is wrong because cloud services run on ordinary bits and servers. Option C is wrong because visible light communication, or Li-Fi, sends data using LED light. Option D is wrong because wireless communication uses radio waves, not qubits. Exam tip: a bit is 0 or 1, a qubit means superposition and entanglement.

The correct answer is C, Epithelial tissue. Epithelium covers the body and lines its organs, so it is the protective tissue.

It forms the outer layer of the skin, the lining of the mouth, stomach, intestine, blood vessels and kidney tubules. Its cells sit tightly packed with almost no material between them, resting on a basement membrane, and they act as a barrier against germs, injury and water loss. Epithelium also takes part in absorption and secretion, which is why glands are made of it. Its types are squamous, cuboidal, columnar, ciliated and glandular.

Option A is wrong because muscular tissue contracts to produce movement. Option B is wrong as nervous tissue carries impulses and controls responses. Option D is wrong because connective tissue, such as bone, cartilage, blood and adipose tissue, joins and supports other tissues rather than covering the body.

Exam tip: the four animal tissues - epithelial protects, muscular moves, nervous conducts, connective supports.

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 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 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.