General Science Mixed Quiz: Set 68

The correct answer is C. The third law does not make one force the cause and the other the effect; action and reaction arise together, at the same instant.

Newton's third law says that to every action there is an equal and opposite reaction. The two forces act on two different bodies, are equal in size, opposite in direction and simultaneous. Because neither comes first, the words action and reaction are only labels; either force can be called the action. This is also why forces always come in pairs in nature.

A is correct and so not the answer: a force is always an interaction between two bodies, so it never occurs alone.

B is correct and so not the answer: the stone pulls the Earth upwards with the same force; the Earth barely moves because its mass is enormous.

D is correct and so not the answer: it is the accurate reading of the law, that action and reaction are simultaneous, with no cause and effect between them.

Exam tip: action and reaction are equal, opposite, simultaneous and act on different bodies, so they never cancel each other.

The correct answer is B, Concrete. Concrete is the building material made by mixing cement with coarse aggregate such as gravel, fine aggregate such as sand, and water.

The cement and water react in a process called hydration, which sets into a hard mass and binds the aggregate together. A common ratio for ordinary work is one part cement, two parts sand and four parts gravel, written as 1:2:4. Concrete is strong in compression but weak in tension, so steel bars are embedded in it to make reinforced cement concrete, the material of most modern buildings, bridges and dams.

Option A, mortar, is cement or lime with sand and water only, with no coarse aggregate, and is used to join bricks. Option C, slurry, is any thin, pourable mix of a solid in a liquid. Option D, a moderator, is the material that slows neutrons in a nuclear reactor.

Exam tip: mortar has no gravel; concrete has gravel; adding steel gives RCC.

The correct answer is B, lowers the boiling point of the liquid. A liquid boils when its vapour pressure equals the pressure above it, so less outside pressure means boiling starts at a lower temperature.

As a liquid is heated, its vapour pressure rises. Boiling begins at the temperature where this vapour pressure matches the external pressure. At sea level, with about 101.3 kPa of pressure, water boils at 100 °C. High in the mountains the air pressure is lower, so water boils at around 70 to 90 °C, which is too cool to cook rice or pulses quickly. A pressure cooker does the opposite: it raises the pressure to about twice the normal value, so water boils near 120 °C and food cooks faster.

A is wrong: raising the pressure, not lowering it, raises the boiling point.

C is wrong: boiling point depends directly on the outside pressure.

D is wrong: with a lower boiling point the liquid reaches boiling sooner, not later.

Exam tip: low pressure, low boiling point (hills); high pressure, high boiling point (pressure cooker).

The correct answer is A, Goat. Capra hircus is the scientific name of the domestic goat, in which Capra is the genus and hircus the species, written in the two-word form that Carl Linnaeus gave to biology. The goat is a ruminant of the family Bovidae and is called the poor man's cow because it gives milk and meat on little feed and thrives in dry country; Rajasthan leads the states in goat population and Sirohi, Marwari, Jakhrana and Barbari are among its known breeds. B is wrong because cattle are Bos indicus, the humped Indian cattle, or Bos taurus. C is wrong because the sheep is Ovis aries. D is wrong because the Indian water buffalo is Bubalus bubalis, the animal that gives most of India's milk. Exam tip: fix the four names together, goat Capra hircus, sheep Ovis aries, cattle Bos indicus and buffalo Bubalus bubalis.

The correct answer is C, total internal reflection. Light inside the fibre strikes the boundary at more than the critical angle, so it is reflected back again and again instead of escaping.

An optical fibre has a glass core surrounded by cladding of slightly lower refractive index. Total internal reflection happens when light travels from a denser to a rarer medium and the angle of incidence is greater than the critical angle. Each time the signal meets the core-cladding boundary it is fully reflected, so it zigzags along the fibre with very little loss, even around gentle bends. This is why fibres carry internet and telephone data over long distances and are used in endoscopes.

A is wrong: interference is the overlapping of waves to form bright and dark bands.

B is wrong: scattering spreads light out, as in the blue sky, and is a source of loss in a fibre.

D is wrong: refraction lets light pass out of the core; the fibre works because light does not refract out.

Exam tip: two conditions for total internal reflection are denser to rarer medium and angle above the critical angle; examples are optical fibre, sparkling diamond and mirage.

The correct answer is D, 2.4. The velocity ratio of a pulley system is the distance moved by the effort divided by the distance moved by the load, so it is 12 divided by 3, that is 4. Efficiency is the mechanical advantage divided by the velocity ratio, so the mechanical advantage is 0.6 multiplied by 4, which gives 2.4. Remember that the velocity ratio depends only on how the machine is built, while the mechanical advantage also falls with friction and with the weight of the pulleys and rope; that is why no real machine reaches an efficiency of 100 per cent and the mechanical advantage is always smaller than the velocity ratio. A is wrong because 4.8 multiplies the velocity ratio by 1.2 instead of 0.6. B is wrong because 3.6 takes 60 per cent of 6, not of 4. C is wrong because 1.2 treats the velocity ratio as 2. Exam tip: efficiency equals mechanical advantage divided by velocity ratio.

The correct answer is C, Doppler effect. A speed radar measures how much the frequency of its reflected wave changes, and that change depends on the speed of the vehicle.

The Doppler effect, described by Christian Doppler in 1842, is the apparent change in the frequency of a wave when the source and the observer move relative to each other. The police gun sends out radio waves of a fixed frequency; a car coming towards it reflects them at a higher frequency, a car moving away at a lower one. The device converts this frequency shift into the speed of the vehicle. The same idea explains the falling pitch of a passing train's horn and the red shift of distant galaxies.

A is wrong: the Raman effect is the scattering of light by molecules with a change of wavelength, found by C. V. Raman in 1928.

B is wrong: induction is about producing current by a changing magnetic field.

D is wrong: Coulomb's law gives the force between electric charges.

Exam tip: speed gun, passing horn and red shift of galaxies all use the Doppler effect.

The correct answer is C, Ear. Balance is controlled by the inner ear, which holds the vestibular apparatus alongside the organ of hearing. It is made of three semicircular canals set at right angles to one another and two small sacs, the utricle and the saccule. The canals are filled with fluid; when the head turns, the fluid lags behind and bends tiny hair cells, which send the brain a signal about the direction and the speed of the movement. The utricle and the saccule report the pull of gravity and straight-line motion. This is why an inner-ear infection, or spinning round quickly, leaves a person giddy. Option A is wrong because the heart only pumps blood through the body. Option B is wrong because the liver makes bile, breaks down toxins and stores glycogen. Option D is wrong because the tongue carries the taste buds and helps in speech and swallowing. Exam tip: the cochlea of the inner ear is for hearing, and the three semicircular canals are for balance.

The correct answer is A, 2 and 1. For a 4d orbital, n = 4 and l = 2, which gives l = 2 angular nodes and n − l − 1 = 1 radial node.

A node is a region where the probability of finding the electron is zero. Angular nodes are planes or cones through the nucleus, and their number equals the azimuthal quantum number l. Radial nodes are spherical shells, and their number is n − l − 1. The total number of nodes is always n − 1. For 4d: l = 2 for any d orbital, so 2 angular nodes; radial nodes = 4 − 2 − 1 = 1; total = 3, which equals n − 1. In the same way 3d has 2 angular and 0 radial nodes, and 2s has 0 angular and 1 radial node.

B is wrong: it reverses the two values.

C is wrong: 3 angular nodes belong to an f orbital (l = 3), not a d orbital.

D is wrong: 4 angular nodes would need l = 4, a g orbital, and the total of 4 exceeds n − 1 = 3.

Exam tip: angular nodes = l, radial nodes = n − l − 1, total nodes = n − 1.

The correct answer is A, Petiole. The petiole is the stalk that joins a leaf blade to the stem; it belongs to the leaf, not to the flower, and a leaf without one is called sessile. A typical flower is built of four whorls borne on the thalamus. The calyx is the outermost ring of sepals, which protect the bud. Inside it the corolla of petals attracts pollinators. Then comes the androecium, the male whorl, whose units are the stamens, each with an anther on a filament. At the centre is the gynoecium, the female whorl, whose unit is the pistil or carpel, made of stigma, style and ovary. Option B is wrong because the pistil is the female part of the flower. Option C is wrong because the stamen is its male part. Option D is wrong because sepals form the calyx, the flower's outermost whorl. Exam tip: the four floral whorls are calyx, corolla, androecium and gynoecium; the petiole is a part of the leaf.

The correct answer is A, fireworks to make a bright white light. Magnesium burns in air with a dazzling white flame, which is why it goes into fireworks, sparklers and flares.

When magnesium ribbon is heated it reacts with oxygen to form white magnesium oxide (2Mg + O2 → 2MgO), giving out intense heat and brilliant white light, including ultraviolet. Pyrotechnic makers add magnesium or magnesium-aluminium alloy powder to brighten colours and produce white sparks; the same property was used in early photographic flash powder. Magnesium is also the central atom of chlorophyll and a light metal used in alloys for aircraft and car parts.

B is wrong: gemstones are minerals such as corundum, beryl or diamond, not magnesium metal.

C is wrong: the alimentary canal is examined with a barium meal, using barium sulphate, which shows up in X-rays.

D is wrong: water is purified with chlorine, bleaching powder, alum or ozone, not magnesium.

Exam tip: magnesium = white flame and the centre of chlorophyll; barium = green flame and the barium meal; strontium = red flame.

The correct answer is B, Static friction > Kinetic friction > Rolling friction. For the same pair of surfaces the order of friction is always static, then kinetic, then rolling. Static friction is the largest because the surfaces interlock while at rest and that grip has to be broken to start motion. Once sliding begins the contact keeps breaking and remaking, so kinetic friction is smaller. Rolling friction is the smallest of the three, since a rolling wheel does not slide over the road but only presses and deforms it slightly at the point of contact. This is exactly why wheels, rollers and ball bearings are used to shift heavy loads. A and D are wrong because they place rolling friction at the top, though it is the least of the three. C is wrong because it puts rolling friction above kinetic friction, reversing the true order. Exam tip: static greater than kinetic greater than rolling; the smallest of them gave us the wheel.

The correct answer is C, Cell wall. Animal cells are bounded only by a flexible cell membrane; a rigid cell wall is found in plants, fungi and bacteria.

In plant cells the cell wall lies outside the cell membrane and is made mainly of cellulose; it gives shape, strength and protection against bursting when the cell takes in water. Fungi have walls of chitin and bacteria of peptidoglycan. Animal cells lack it, which lets them change shape, move and form tissues such as muscle. Other structures usually absent from animal cells are chloroplasts and a large central vacuole, while centrioles are typical of animal cells.

A is wrong: the cell membrane (plasma membrane) surrounds every living cell, animal or plant.

B is wrong: the endoplasmic reticulum, which makes proteins and lipids, is present in animal cells.

D is wrong: lysosomes, the digestive bags called suicide bags of the cell, are characteristic of animal cells.

Exam tip: plant cell = cell wall, chloroplast, large vacuole; animal cell = centrioles and lysosomes, no cell wall.

The correct answer is D, Charles’s law. Charles’s law says that at constant pressure the volume of a fixed mass of gas is directly proportional to its absolute temperature, so V by T stays constant. Jacques Charles studied this in 1787, and Joseph Gay-Lussac published the quantitative form in 1802. Written as a ratio it gives V1 by T1 equals V2 by T2, with the temperature always taken in kelvin. Extending the volume-temperature graph backwards to zero volume gives absolute zero, minus 273.15 degrees Celsius, which is how the kelvin scale was fixed. A is wrong because Boyle’s law relates pressure and volume at constant temperature, with PV constant. B is wrong because Dalton’s law of partial pressures adds the pressures of the gases in a mixture. C is wrong because Avogadro’s law links equal volumes of gases to equal numbers of molecules. Exam tip: keep the three apart - Boyle for P and V, Charles for V and T, Gay-Lussac for P and T.

The correct answer is D, 1, 2 and 3. All three are adaptations of desert plants (xerophytes) that cut down water loss through transpiration.

Plants lose most of their water through the leaves, so desert plants change their leaves to save it. A thick waxy cuticle makes the leaf surface hard and waterproof, as in the oleander and many succulents. Small leaves expose less surface to the hot, dry air, as in acacia and tamarisk. In cacti and some euphorbias the leaves are reduced to spines or thorns, and the green fleshy stem takes over photosynthesis and stores water. Sunken stomata and fewer stomata are other such features.

A is wrong because it leaves out hard, waxy leaves.

B is wrong because tiny leaves are only one of the three adaptations.

C is wrong because thorns are not the only change seen in desert plants.

Exam tip: cactus = leaves turned into spines, stem does photosynthesis; xerophytes = waxy cuticle, small leaves, sunken stomata.

The correct answer is A, Crown Gall. Crown gall is caused by the bacterium Agrobacterium tumefaciens, which enters through a wound near the base, or crown, of the stem and makes the plant grow rough tumour-like swellings there. The bacterium works by pushing a piece of its own Ti plasmid into the plant's cells and forcing them to divide, and that natural trick is why laboratories use it as a vector to carry new genes into plants. Grapevine, apple, rose, walnut and stone fruits suffer the most. Option B is wrong because mosaic diseases, such as tobacco mosaic, are caused by viruses that mottle the leaves in light and dark patches. Option C is wrong because smut of wheat, bajra and sugarcane is a fungal disease that fills the ear with black powdery spores. Option D is wrong because white blister, or white rust, of crucifers such as mustard is also fungal and raises white blisters on leaves and stems. Exam tip: bacterial — crown gall, citrus canker, bacterial blight of rice; viral — mosaic, leaf curl; fungal — smut, rust, blight.

The correct answer is A, 5 cm, converging. A real, inverted image of the same size forms only when the object sits at twice the focal length of a convex lens, so 2f = 10 cm and f = 5 cm.

For a convex (converging) lens, an object placed at 2F gives a real, inverted image of equal size at 2F on the other side. Check with the lens formula 1/v − 1/u = 1/f: with u = −10 cm and v = +10 cm, 1/f = 1/10 + 1/10 = 1/5, so f = +5 cm. A positive focal length confirms a converging lens. Magnification m = v/u = −1, which means same size and inverted.

B is wrong: a diverging (concave) lens always forms a virtual, erect and diminished image, never a real one.

C is wrong: with f = 20 cm the object at 10 cm would be inside the focus and the image would be virtual and enlarged.

D is wrong: a concave lens cannot form a real image, whatever its focal length.

Exam tip: convex lens, object at 2F gives image at 2F, real, inverted and the same size; u = v = 2f.

The correct answer is A, phenol. Bakelite is a phenol-formaldehyde resin, prepared by condensing phenol with formaldehyde; on curing the chains cross-link into a rigid network, giving a hard, heat-resistant and electrically insulating solid used for switches, plug tops, pan handles and distributor caps. It was the first wholly synthetic plastic. B, melamine, is wrong because melamine with formaldehyde gives melamine-formaldehyde resin, the material of unbreakable crockery. C, urea, is wrong because urea with formaldehyde gives urea-formaldehyde resin, used in adhesives, laminates and foam insulation. All three are thermosetting resins of formaldehyde, which is why examiners group them, so remember the pairing of each one with its partner. D, aniline, is wrong; it is used in making dyes and drugs, not bakelite. So learn the three formaldehyde resins as a set of pairs and the question becomes a single step.

The correct answer is B, Carolus Linnaeus. The Swedish naturalist Carl von Linne, known in Latin as Carolus Linnaeus, arranged plants and animals in a hierarchy of ranks and gave biology the two-word system of scientific names in his works Systema Naturae and Species Plantarum, so he is called the father of taxonomy. A is wrong because Charles Darwin explained how species change by natural selection in On the Origin of Species, which is the foundation of evolutionary biology rather than of naming and ranking. C is wrong because Ernst Haeckel added the kingdom Protista for single-celled organisms, an important step but long after the system of naming had been settled. D is wrong because Robert Hooke first saw and named cells in a thin slice of cork and belongs to the history of cytology.

The correct answer is A, Bacteria contain cytoplasm but viruses do not. A bacterium is a living cell filled with cytoplasm, while a virus is only genetic material inside a protein coat.

Bacteria are prokaryotic cells: they have a cell wall, a cell membrane, cytoplasm with ribosomes, and a circular DNA, but no nucleus bounded by a membrane and no membrane-bound organelles. Viruses are not cells at all. A virus particle (virion) is DNA or RNA wrapped in a protein capsid, sometimes with an outer envelope taken from the host. It has no cytoplasm, ribosomes or metabolism of its own, so it can multiply only inside a living host cell. This is why antibiotics act on bacteria but not on viruses.

B is wrong: bacteria, being prokaryotes, have no mitochondria.

C is wrong: viruses have no organelles, and bacteria have no mitochondria either.

D is wrong: bacteria do have a cell membrane, and viruses have no cell membrane, only a capsid and sometimes an envelope.

Exam tip: bacteria = prokaryotic cell, no mitochondria, killed by antibiotics; virus = nucleic acid + protein coat, not a cell.