General Science Mixed Quiz: Set 10

The correct answer is D, Volt. Potential difference is the work done to move a unit charge between two points, and its SI unit is the volt. V = W/Q, so 1 volt = 1 joule per coulomb. It is measured with a voltmeter, which is always connected in parallel across the part of the circuit being tested. The unit is named after Alessandro Volta, the Italian scientist who made the first electric battery, the voltaic pile. Household supply in India is 230 V, while a pencil cell gives 1.5 V. A is wrong because the ampere is the unit of electric current, measured with an ammeter joined in series. B is wrong because the tesla is the unit of magnetic field strength (magnetic flux density). C is wrong because the coulomb is the unit of electric charge; one coulomb is the charge of about 6.25 × 10¹⁸ electrons. Exam tip: Current = ampere, Charge = coulomb, Potential difference = volt, Resistance = ohm, Power = watt, Energy = joule.

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 A, the law of inertia. The first law states that a body continues in its state of rest or of uniform motion in a straight line unless an unbalanced external force acts on it, which is exactly the property called inertia.

Option B refers to the second law, which deals with the rate of change of momentum and yields the equation force equals mass times acceleration. Option C is the third law, which says that action and reaction are equal and opposite and act on different bodies. Option D, the law of gravitation, is a separate law of Newton's, stating that every body attracts every other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. The first law also defines force, by telling us that a force is what is needed to change a state of motion.

The correct answer is C, Anabaena. Anabaena is a cyanobacterium, a prokaryote with no true nucleus, and all prokaryotes are placed in Monera. In R.H. Whittaker's five-kingdom classification (1969), Monera holds the bacteria and the cyanobacteria, or blue-green algae, whose cells have no nuclear membrane and no membrane-bound organelles. Anabaena grows as chains of cells and has special thick-walled cells called heterocysts that fix nitrogen from the air. It lives inside the small water fern Azolla, which is why Azolla is used as a biofertiliser in paddy fields. Option A is wrong because diatoms are single-celled eukaryotes with glass-like silica walls, placed in Protista; their deposits form diatomaceous earth. Option B is wrong because Euglena is a protist that makes its own food in light but feeds like an animal in the dark. Option D is wrong because Ulothrix is a filamentous green alga with a true nucleus, grouped with plants. Exam tip: no true nucleus means Monera; Anabaena and Nostoc are the nitrogen-fixing cyanobacteria to remember.

The correct answer is B, joule. Work is the product of force and displacement, so its unit is the newton metre, which is given the name joule; one joule of work is done when a force of one newton moves a body through one metre in its own direction. Energy is measured in the same unit, because work done is energy transferred.

Option A, the newton, is the SI unit of force alone. Option C, the watt, is the unit of power, that is the rate of doing work, and equals one joule per second. Option D, the pascal, is the unit of pressure and equals one newton per square metre. Candidates who confuse the joule with the watt lose marks in the very next question of a paper, so learn the pair as work in joule and power in watt.

The correct answer is A, 20 Hz – 20000 Hz. A healthy human ear can hear sound waves with frequencies from about 20 hertz to 20,000 hertz (20 kHz); this band is called the audible range. Sounds below 20 Hz are called infrasonic, and animals such as elephants and whales use them to communicate over long distances. Sounds above 20 kHz are called ultrasonic; bats, dogs and dolphins can hear them, and ultrasound is used in medical scans, in cleaning delicate parts and in SONAR. Children under five and some animals can hear up to about 25 kHz, and the upper limit falls as people grow older. Option B is wrong because 80 to 100 Hz is only a tiny slice of the audible range. Option C is wrong because 2 lakh to 4 lakh Hz, that is 200 to 400 kHz, lies far inside the ultrasonic range. Option D is wrong because 0 to 20 Hz is the infrasonic range, which humans cannot hear. Exam tip: infrasonic below 20 Hz, audible from 20 Hz to 20 kHz, ultrasonic above 20 kHz.

The correct answer is D, 80 J. The work done in moving a charge across a potential difference is W = QV, so W = 5 × 16 = 80 joules. Potential difference is itself defined as the work done per unit charge in carrying that charge from one point to another, which is why one volt means one joule of work for every coulomb moved. Here five coulombs are carried across sixteen volts, so the source must supply 80 J of energy. A is wrong because 65 J does not follow from any correct use of 5 C and 16 V. B is wrong because 45 J would need a potential difference of 9 V for the same charge. C is wrong because 40 J would need either 2.5 C at 16 V or 5 C at 8 V. Exam tip: remember V = W/Q, so W = QV; in this chapter joules are simply coulombs multiplied by volts.

The correct answer is D, Fleming's Left-Hand Rule. It gives the direction of the force, and so of the motion, on a current-carrying conductor placed in a magnetic field, which is exactly what turns the coil of a motor. Stretch the thumb, forefinger and middle finger of the left hand so that they are at right angles to one another. If the forefinger points along the magnetic field and the middle finger along the current, the thumb points in the direction of the force. The force is greatest when the current is at right angles to the field. A is wrong because Ampere's law relates the magnetic field around a closed loop to the current passing through it. B is wrong because the right-hand thumb rule finds the direction of the magnetic field lines around a straight current-carrying wire. C is wrong because Fleming's right-hand rule gives the direction of the induced current in a generator. Exam tip: left hand for motor, right hand for generator; forefinger = field, middle finger = current, thumb = motion.

The correct answer is C, Zn. Zinc has atomic number 30, which means each of its atoms carries 30 protons in the nucleus. In the modern periodic table the elements are arranged in increasing order of atomic number, as Moseley showed, and zinc sits in group 12 of the fourth period at the end of the first transition series. It is a bluish-white metal that is used to galvanise iron against rust, in dry cells and in brass, an alloy of copper and zinc. A is wrong because nickel (Ni) has atomic number 28. B is wrong because iron (Fe) has atomic number 26 and is the most used metal in the world. D is wrong because cobalt (Co) has atomic number 27 and is the metal at the centre of vitamin B12. Exam tip: learn the run 24 to 30 in order — Cr, Mn, Fe, Co, Ni, Cu, Zn.

The correct answer is B, 14 : 3. Ammonia is NH3, so one nitrogen atom of mass 14 is joined to three hydrogen atoms of mass 1 each, giving 14 : 3 by mass. This is the law of constant proportions given by Proust in 1799: a pure compound always contains the same elements in the same ratio by mass, whatever its source. The NCERT Class 9 chapter uses exactly these examples, water H2O with hydrogen to oxygen 1 : 8 and ammonia NH3 with nitrogen to hydrogen 14 : 3. Remember that the ratio by mass is not the ratio by atoms; by atoms ammonia is 1 : 3, by mass it is 14 : 3 because nitrogen is fourteen times heavier than hydrogen. A is wrong because 11 is not the atomic mass of nitrogen. C is wrong for the same reason, even though the hydrogen part is right. D is wrong because it counts only one hydrogen atom instead of three. Exam tip: water 1 : 8, ammonia 14 : 3, carbon dioxide 3 : 8, all by mass.

The correct answer is A, Peacock. The peacock is a bird, and all birds, like mammals, have a heart of four chambers: two atria and two ventricles. Four chambers keep oxygen-rich blood and oxygen-poor blood completely apart, so the body gets fully oxygenated blood. Birds and mammals need this because they are warm-blooded and burn a great deal of energy to hold a steady body temperature; flight makes the demand greater still. Crocodiles are the only reptiles with a four-chambered heart. B is wrong because a sea horse is a fish and has a two-chambered heart, one atrium and one ventricle. C is wrong because a frog, being an amphibian, has three chambers, two atria and a single ventricle in which the two kinds of blood mix. D is wrong for the same reason as the sea horse. Exam tip: fish 2 chambers, amphibians and most reptiles 3, birds and mammals 4; the peacock is India's national bird.

The correct answer is D, (i) - (c), (ii) - (b), (iii) - (a). Red cabbage is a natural acid-base indicator, methyl orange is a synthetic acid-base indicator, and onion and clove are olfactory indicators. An indicator tells whether a solution is acidic or basic. Natural indicators come from plants: litmus from lichen, turmeric, red cabbage leaves and coloured petals such as hydrangea and petunia. Synthetic indicators made in the laboratory include methyl orange, which is red in acid and yellow in base, and phenolphthalein, which is colourless in acid and pink in base. Olfactory indicators change their smell instead of their colour; onion, vanilla and clove lose their smell in a basic solution. A is wrong because it calls methyl orange an olfactory indicator. B is wrong because it labels red cabbage as olfactory. C is wrong because it puts onion and clove under natural colour indicators. Exam tip: change of smell = olfactory (onion, clove, vanilla); change of colour = litmus, turmeric, red cabbage; lab-made = methyl orange, phenolphthalein.

The correct answer is D, Fibrous roots. Fibrous roots are the mark of monocotyledonous plants such as wheat, maize, rice and grasses, not of dicots. A dicot seed carries two cotyledons, and its seedling sends down one strong primary root that thickens into a tap root with smaller lateral branches; gram, pea, mustard, neem and mango are familiar examples. Dicot leaves show reticulate or net-like venation, their flowers usually have petals in fours or fives, and their vascular bundles stand in a ring with cambium, so the stem can thicken year after year. A is wrong because the tap root is precisely what a dicot has. B is wrong because reticulate venation is a dicot feature, while monocots show parallel venation. C is wrong because two cotyledons is the very definition of a dicotyledonous plant. Exam tip: dicot - two cotyledons, tap root, reticulate venation; monocot - one cotyledon, fibrous roots, parallel venation.

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 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 D, Magnesium hydroxide. Milk of magnesia is a white suspension of magnesium hydroxide, Mg(OH)2, in water, and its milky look gives it the name. It is a mild base, so it is taken as an antacid to neutralise excess hydrochloric acid in the stomach and relieve acidity; in larger doses it works as a laxative. Being only slightly soluble, it does not make the stomach strongly alkaline, which is why it is safe as a medicine. A, Magnesium bicarbonate, exists only in solution and is not used as a medicine. B, Magnesium carbonate, is used in chalk and as a drying powder for the hands in sports, and is not called milk of magnesia. C, Magnesium sulphate, is Epsom salt, used in bath salts and as a purgative. Exam tip: pair the common names: milk of magnesia is Mg(OH)2, Epsom salt is MgSO4.7H2O, milk of lime is a Ca(OH)2 suspension.

The correct answer is C, displacement. It is the shortest distance from the starting point to the finishing point together with the direction of that straight line, so it has both magnitude and direction and is therefore a vector.

Option A, distance, is the total length of the path travelled and carries no direction, so it is a scalar; option B, speed, is distance divided by time and is a scalar for the same reason, while velocity, which is displacement divided by time, is a vector. Option D, time, is a scalar. The standard illustration is a runner completing one lap of a circular track: the distance covered equals the circumference, but the displacement is zero because the runner ends where the lap began. Remember the pairs, distance with speed as scalars and displacement with velocity as vectors.

The correct answer is C, 90 degrees. Work equals force into displacement into the cosine of the angle between them, and the cosine of ninety degrees is zero, so a force at right angles to the motion does no work at all. This is why the centripetal force in circular motion does no work and why a person carrying a load on the head along a level road does none against gravity.

Option A, zero degrees, gives the maximum positive work, since the cosine of zero is one and force and displacement point the same way. Option B, forty five degrees, gives partial positive work, as the cosine is about 0.707. Option D, 180 degrees, gives the maximum negative work, the case of friction opposing motion. Learning the four cosine values, one, 0.707, zero and minus one, settles this whole family of questions.

The correct answer is B, the same, opposite. The same magnet moves at the same speed in both cases, so the rate of change of magnetic flux through the coil is equal and the induced potential difference has the same magnitude. But turning the other pole towards the coil reverses the direction of the field through it, so the induced voltage takes the opposite sign. This follows from Faraday's law of electromagnetic induction, which says the induced emf equals the rate of change of flux, and from Lenz's law, which fixes the direction so that the induced current opposes the change causing it. A is wrong because the sign must flip once the pole facing the coil is reversed. C is wrong because the speed, and therefore the rate of flux change, is unchanged, so the two magnitudes match. D is wrong on both counts. Exam tip: speed decides how big the induced emf is, the field direction decides its sign - Faraday for magnitude, Lenz for direction.

The correct answer is A, During respiration. Plants respire day and night, breaking glucose down to release energy, and carbon dioxide is the waste product of that process. Photosynthesis does the opposite: the plant takes in carbon dioxide and water and, using sunlight trapped by chlorophyll, makes glucose while releasing oxygen as its waste product. During the day photosynthesis runs faster than respiration, so a green plant gives out oxygen on balance; at night only respiration continues, so carbon dioxide is released. These gases move in and out through the stomata of leaves and the lenticels of woody stems. B is wrong because photosynthesis uses carbon dioxide up instead of producing it. C is wrong for the same reason, as oxygen and not carbon dioxide is the waste of photosynthesis. D is wrong because transpiration is the loss of water vapour from the plant and involves no carbon dioxide. Exam tip: respiration takes oxygen and gives carbon dioxide; photosynthesis takes carbon dioxide and gives oxygen.