General Science Mixed Quiz: Set 14

The correct answer is B, 19.8 × 10⁶ J. One kilowatt hour is 3.6 × 10⁶ joule, so 5.5 kWh = 5.5 × 3.6 × 10⁶ = 19.8 × 10⁶ joule.

The kilowatt hour is the commercial unit of electrical energy, the unit in which the electricity board bills a house, and it is often called one unit of electricity. It comes from energy = power × time, so one kilowatt of power drawn for one hour means 1000 watt × 3600 second = 3600000 joule. The joule is the SI unit of energy, and one watt is one joule per second.

Option A is wrong because 14.0 × 10⁶ J is about 3.9 kWh. Option C is wrong because 14.4 × 10⁸ J would be 400 kWh, a hundred times too large. Option D is wrong because 14.4 × 10⁵ J is only 0.4 kWh.

Exam tip: 1 kWh = 3.6 × 10⁶ J = one unit of electricity; multiply the number of units by 3.6 million to get joule.

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 B, Friction. Brakes work on friction: a lining is pressed against a moving drum or disc, and the rubbing force slows the wheel down. Friction is the force that opposes motion between two surfaces in contact. In a drum brake the shoes push outward against the inner face of the drum, while in a disc brake the pads grip a rotating disc from both sides; in each case the kinetic energy of the vehicle is turned into heat, which is why brakes grow hot on a long downhill run. The friction between the tyre and the road then stops the vehicle itself, so a smooth or wet road lengthens the stopping distance. Option A is wrong because vibration only shakes a body and cannot take away its energy in a controlled way. Option C is wrong because suction is a pressure difference; a vacuum booster only helps the driver press the pedal, it does not stop the wheel. Option D is wrong because dragging is not a physical principle. Exam tip: brakes turn kinetic energy into heat through friction.

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 C, 16 times the initial value. Kinetic energy depends on the square of the momentum, so the momentum grows as the square root of the energy. For a body of mass m, the kinetic energy can be written as p squared divided by 2m, where p is the linear momentum. If the mass does not change, p equals the square root of 2mE, so p is proportional to the square root of E. When the kinetic energy becomes 256 times, the momentum becomes the square root of 256, that is 16 times its earlier value, and the speed also becomes 16 times. Option A is wrong because a body cannot gain energy while its momentum stays the same. Option B is wrong because 8 times the momentum would make the energy 64 times, not 256 times. Option D is wrong because 32 times the momentum would make the energy 1024 times. Exam tip: E equals p squared by 2m, so if the energy becomes n times the momentum becomes root n times, and if the momentum becomes n times the energy becomes n squared times.

The correct answer is C, Newtonian telescope. Isaac Newton built the first practical reflecting telescope in 1668. In it, light from the star falls on a large concave mirror at the bottom of the tube, and a small flat mirror set at 45 degrees near the top turns the light sideways to the eyepiece. Because the objective is a mirror and not a lens, there is no chromatic aberration, the colour fringing that lenses produce, and a mirror can be made much larger and lighter than a lens. Most big observatory telescopes are therefore reflectors. A, the Galilean telescope, is a refractor using a convex objective lens and a concave eyepiece lens. B, the Keplerian telescope, is also a refractor, with two convex lenses, and gives an inverted image. D, the Schmidt telescope, is a catadioptric design that combines a spherical mirror with a glass corrector plate, so it is not mirrors only. Exam tip: refractor means lenses (Galileo, Kepler), reflector means mirrors (Newton), Schmidt means a mirror plus a corrector lens.

The correct answer is B, the poles. The earth is flattened at the poles, so the distance from the centre is least there, and since g varies inversely as the square of that distance, g is largest at the poles. The rotation of the earth also reduces the effective value of g, and that reduction is greatest at the equator and zero at the poles, which adds to the difference.

Option A, the equator, is where g has its smallest surface value, for exactly the opposite reasons. Option C, the centre of the earth, is where g becomes zero, since the mass of the earth then surrounds the body on all sides and its pulls cancel out; a body there has weight zero although its mass is unchanged. Option D, the top of Mount Everest, is far above sea level, and g decreases with height, so it is smaller there than at sea level. The order worth remembering is poles greatest, equator smaller, height smaller still, centre zero.

The correct answer is B, A bottle opener. Levers are grouped by where the fulcrum, the load and the effort sit. In a second class lever the load lies between the fulcrum and the effort. In a bottle opener the rim of the cap is the fulcrum at the tip, the cap being lifted is the load in the middle, and your hand applies the effort at the far end. Such levers always multiply force because the effort arm is longer; a wheelbarrow and a nutcracker work the same way. A, A pair of scissors, is a first class lever, with the pivot between the effort and the load. C, A cricket bat, is a third class lever: the lower hand applies the effort between the top hand, which acts as the fulcrum, and the ball. D, A bow and arrow, works by storing energy in the bent bow like a spring, not by placing the load between the fulcrum and the effort. Exam tip: first class has the fulcrum in the middle, second class the load in the middle, third class the effort in the middle.

The correct answer is B, 4 degrees Celsius. Water behaves abnormally between zero and four degrees: it contracts as it is heated in that range and expands again above four degrees, so the same mass occupies its least volume, and therefore has its greatest density, at four degrees Celsius.

Option A is the freezing point, where water turns to ice; ice is in fact less dense than water, which is why it floats. Option C is the boiling point at normal atmospheric pressure, where water is at its most expanded as a liquid. Option D lies below the freezing point, where pure water at ordinary pressure is solid. The property matters in nature because in a pond in winter the water at four degrees sinks, the colder water floats and freezes at the top, and fish survive in the liquid water below.

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 C, 10 Joule. Potential difference is defined as the work done for each unit of charge carried between two points, so V = W/Q and therefore W = QV. Here the charge is 2 coulomb and the potential difference is 5 volt, which gives work of 2 into 5, that is 10 joule. The definition is the whole question: one volt is one joule per coulomb, so a charge of two coulomb moving across five volt must take ten joule of work. Option A, 0.4 joule, comes from dividing the charge by the voltage instead of multiplying. Option B, 2.5 joule, comes from dividing the voltage by the charge, which gives volt per coulomb and not an energy at all. Option D, 20 joule, is double the right value and would need a charge of 4 coulomb or a potential difference of 10 volt. Exam tip: W = QV, and one volt means one joule of work for every coulomb of charge.

The correct answer is A, Glass powder and red phosphorus. The rough strip of a safety matchbox is coated with powdered glass and a little red phosphorus, while the head of the matchstick carries antimony trisulphide and potassium chlorate. When the match is struck, friction turns some red phosphorus into white phosphorus. This reacts at once with the potassium chlorate in the head and produces enough heat to set the antimony trisulphide burning. Keeping the phosphorus on the box and the other chemicals on the stick is what makes the match safe. NCERT's Class 8 science book adds that early matches used white phosphorus, which proved dangerous for the workers who made them and for users. B is wrong because white phosphorus is not used on the rubbing surface of a safety match. C is wrong because magnesium is not part of the striking strip. D is wrong because neither potassium nor white phosphorus is found on the strip. Exam tip: box strip, red phosphorus plus glass powder; match head, antimony trisulphide plus potassium chlorate.

The correct answer is B, Platinum. Platinum is the least reactive of the four, so it is found in nature in the free or native state as the metal itself.

A metal occurs free only when it does not react with the air, water and other substances around it. In the reactivity series the metals at the bottom - gold, platinum and silver - are called noble metals and are found native; those higher up occur as oxides, sulphides or carbonates and must be extracted from their ores. This is why gold nuggets are found in river sand while aluminium has to be won from bauxite by electrolysis.

Option A is wrong because copper is mostly mined as copper pyrites and other ores, though small native deposits do exist. Option C is wrong because iron is always found as an oxide such as haematite or magnetite. Option D is wrong because potassium is so reactive that it burns on contact with water and is never found free.

Exam tip: gold, platinum and silver occur native; the more reactive a metal, the more firmly it stays locked in its ore.

The correct answer is B, Both I and II. Both pairs are wrong. Amyloplasts store starch, a carbohydrate, and aleuroplasts store proteins; oils and fats are stored by elaioplasts. Plastids are organelles found only in plant cells. Chloroplasts hold chlorophyll and do photosynthesis, chromoplasts hold the yellow, orange and red pigments of flowers and fruits, and leucoplasts are colourless storage plastids. The leucoplasts are named after what they keep: amyloplasts keep starch (amylum), as in potato tubers; elaioplasts keep oils (elaion means oil), as in castor seeds; aleuroplasts keep proteins (aleurone), as in the outer layer of wheat grains. A is wrong because it accepts pair II, which links aleuroplasts to carbohydrates instead of proteins. C is wrong because it treats both pairs as correct. D is wrong because it accepts pair I, which links amyloplasts to fats instead of starch. Exam tip: amylo = starch, elaio = oil, aleuro = protein; all three are leucoplasts.

The correct answer is B, The stamen and pistil. The stamen and the pistil make the male and female gametes, so they are the essential or reproductive organs of a flower. The stamen is the male part and has an anther that produces pollen grains and a filament that holds the anther up. The pistil, also called the carpel, is the female part and has three portions: the stigma that receives the pollen, the style, and the ovary that holds the ovules. After pollination and fertilisation the ovary grows into the fruit and the ovules become seeds. Sepals and petals are called accessory organs because they only protect the bud and attract insects for pollination. Option A is wrong because the sepal is only the green leaf-like part that covers the bud. Option C is wrong because neither sepals nor petals take any part in making gametes. Option D is wrong because the petal is accessory, even though the pistil named with it is essential. Exam tip: stamen and pistil are essential, sepal and petal are accessory.

The correct answer is C, more than the atmospheric pressure. Air always moves from a region of higher pressure to one of lower pressure, so it flows out of the lungs only when the pressure inside them rises above that of the outside air. During expiration the diaphragm relaxes and moves up into its dome shape, and the intercostal muscles between the ribs relax, so the ribs move down and inward. This reduces the volume of the chest cavity, which raises the pressure in the lungs and pushes the air out. Inspiration is the reverse: the diaphragm contracts and flattens, the chest cavity grows, lung pressure falls below atmospheric pressure and air rushes in. Option A is wrong because when the pressures are equal no air moves; this happens for a moment between breaths. Option B is wrong because lower pressure inside the lungs draws air in, which is inspiration. Option D is wrong because contraction of the diaphragm enlarges the chest and causes inspiration, not expiration. Exam tip: inspiration means the diaphragm contracts and lung pressure falls; expiration means it relaxes and lung pressure rises.

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 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 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, 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.