General Science Mixed Quiz: Set 17

The correct answer is C, 500 W. The work done against gravity is mgh = 40 × 10 × 5 = 2000 joule, and power is work divided by time, so 2000 ÷ 4 = 500 watt.

Power is the rate of doing work, measured in watt, where one watt is one joule per second. In climbing stairs the useful work is the gain in potential energy, mgh, where only the vertical rise counts and the length of the staircase does not matter. If the same girl ran up in 2 seconds the work would be the same 2000 joule but the power would double to 1000 watt, which shows that power depends on how fast the work is done.

Option A is wrong because 100 W comes from dividing by the wrong quantity. Option B is wrong because 200 W would need 10 seconds. Option D is wrong because 2000 is the work in joule, not the power in watt.

Exam tip: work = mgh, power = work ÷ time, and one horsepower is about 746 watt.

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, Henry Cavendish. In 1798 Cavendish used a delicate torsion balance to measure the extremely small attraction between lead spheres in a laboratory and from it obtained a value of G, about 6.674 times ten to the power minus eleven newton metre squared per kilogram squared. Since G appears in the formula for g, the same experiment also gave the mass and mean density of the earth, which is why it is popularly called weighing the earth.

Option A, Isaac Newton, stated the law of universal gravitation in the seventeenth century but never measured G, which is why the constant remained unknown in his lifetime. Option C, Galileo Galilei, showed that bodies of different masses fall with the same acceleration and studied projectile motion, but did not work on G. Option D, Johannes Kepler, gave the three laws of planetary motion that Newton later explained using gravitation. Keep the pair Cavendish and G firmly apart from Newton and the law itself.

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 A, 40 per cent. The efficiency of an ideal Carnot engine is one minus the ratio of the sink temperature to the source temperature, both in kelvin. Here the ratio is 300 divided by 500, that is 0.6, and one minus 0.6 is 0.4, which is 40 per cent.

Option B, 60 per cent, is the ratio itself rather than the efficiency, the answer of a candidate who forgets to subtract from one. Option C, 20 per cent, comes from dividing the difference of the two temperatures by their sum, which is not the formula. Option D, about 66.7 per cent, comes from dividing the source by the sink, again a misuse of the formula. Note also that the temperatures must be in kelvin; using degrees Celsius in this formula gives a wrong answer every time.

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 C, the shape and area of the base of the vessel. The pressure at a point inside a liquid equals the depth multiplied by the density of the liquid and by the acceleration due to gravity. Nothing in that expression refers to the shape of the container, so a narrow tube and a wide tank filled to the same level show the same pressure at the same depth, a result demonstrated by the classic hydrostatic paradox.

Option A is wrong as an answer because pressure does rise with depth, which is why a dam is built thicker at the bottom and why a diver feels increasing pressure on descending. Option B is wrong because a denser liquid such as mercury gives a far greater pressure than water at the same depth. Option D is wrong because the term g appears directly in the formula, so the same column of liquid would exert less pressure on the moon. The question asks for the factor that does not matter, so read the wording carefully.

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. A cooker is sealed, so the steam it produces cannot escape and the pressure inside rises. Since the boiling point of a liquid rises with the pressure on it, water in a cooker boils well above a hundred degrees Celsius, and food cooking at that higher temperature is ready sooner.

Option B states the opposite and describes what happens on a mountain, where the pressure is low, water boils below a hundred degrees and cooking takes longer. Option C is wrong as a reason, and the burning power of steam comes from its latent heat rather than from specific heat. Option D is wrong because the material of the vessel affects only how quickly heat reaches the water; it cannot raise the temperature at which the water boils, which is what saves the time.

The correct answer is B, Iron rod. An iron rod is a solid, and the force of attraction between particles is strongest in the solid state.

In a solid the particles sit close together in fixed positions and can only vibrate, so a solid keeps its shape, has a definite volume and can hardly be compressed. In a liquid the attraction is weaker, so the particles slide over one another and the liquid takes the shape of its vessel while keeping its volume. In a gas the attraction is weakest and the particles move freely at high speed, so a gas fills any container and is easily compressed. The same order explains why solids have the highest density and gases the lowest.

Option A is wrong because water is a liquid with medium attraction. Option C is wrong because alcohol is also a liquid, and it evaporates faster than water. Option D is wrong because oxygen is a gas, where the attraction between particles is the weakest of all.

Exam tip: force of attraction is solid greater than liquid greater than gas, and the freedom of particles runs the other way.

The correct answer is B, the spacecraft and the astronaut are both in free fall around the earth. In orbit the gravitational pull of the earth is the very force that keeps the craft curving around the planet, and the craft, the astronaut and everything inside accelerate towards the earth at the same rate. Since the floor no longer pushes up on the astronaut, nothing presses on anything else and the sensation of weight disappears, although true weight is not zero.

Option A is a common misconception: gravity at the height of a low orbit is only slightly less than at the surface, certainly not absent. Option C is wrong because mass is the quantity of matter in a body and does not change with position; it is the apparent weight that vanishes. Option D is wrong because leaving the atmosphere has no bearing on gravitational force, which acts through empty space. The phrase to remember is that weightlessness is a state of free fall, not a state without gravity.

The correct answer is C, Boron. Boron has three electrons in its outermost shell, so it is a trivalent element and is used as a p-type dopant. When a trivalent atom such as boron, aluminium, gallium or indium is added to silicon or germanium, it can form only three covalent bonds with its four neighbours, so one bond is left incomplete. That empty place is called a hole, it behaves like a positive charge carrier, and the doped crystal becomes a p-type semiconductor in which holes are the majority carriers. Adding a pentavalent atom instead leaves a free electron and gives an n-type semiconductor. Option A is wrong because arsenic has five valence electrons and is pentavalent. Option B is wrong because antimony is also pentavalent and is used for n-type doping. Option D is wrong because phosphorus has five valence electrons and donates an electron to the crystal. Exam tip: trivalent dopants such as boron, aluminium, gallium and indium give p-type material, while pentavalent ones such as phosphorus, arsenic and antimony give n-type.

The correct answer is B, adiabatic. An adiabatic change is one in which no heat is exchanged with the surroundings. The bursting of a tyre happens so quickly that the escaping air has no time to take in or give out heat; it does work in expanding, its internal energy falls and it therefore cools, which is why the escaping air feels cold.

Option A, isothermal, is a change at constant temperature, which requires the process to be slow enough for heat to flow in or out and keep the temperature fixed. Option C, isobaric, is a change at constant pressure, such as the heating of a gas under a freely moving piston. Option D, isochoric, is a change at constant volume, such as heating a gas in a rigid closed vessel. The rise of moist air that forms cloud is another everyday adiabatic process.

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, Absolute pressure. Absolute pressure is counted from the absolute zero of pressure, which is a perfect vacuum, so it can never be negative. The working relation is simple: absolute pressure equals gauge pressure plus atmospheric pressure. A tyre showing 30 units on a gauge is really at 30 plus the local atmospheric pressure. Option A is wrong because gauge pressure is measured above the atmospheric pressure of the place, which is why an ordinary pressure gauge reads zero when it is open to the air even though air is pressing on it. Option C is wrong because vacuum pressure, also called negative gauge pressure, is the amount by which a pressure falls below atmospheric. Option D is wrong because atmospheric pressure is the weight of the air column above a place and is about 101.325 kilopascal, equal to 760 millimetres of mercury or 1.01325 bar at sea level. Exam tip: absolute equals gauge plus atmospheric, and only absolute pressure starts from a perfect vacuum.

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, one to two to three. If each length of a solid grows by a certain small fraction when it is heated, an area, which is the product of two lengths, grows by about twice that fraction, and a volume, the product of three lengths, by about three times. So the superficial coefficient is twice the linear and the cubical is three times the linear.

Option B reverses the order and would mean that a body expands least in volume, which is the opposite of what happens. Option C would be true only if area and volume did not depend on more than one length, which is not the case. Option D follows no rule at all. This ratio explains why gaps are left between rails and why a bimetallic strip of two metals with different linear coefficients bends when heated and works as a switch in a thermostat.

The correct answer is D, equal to its weight. A floating body is at rest, so the upward buoyant force must exactly balance the downward weight of the object. By Archimedes' principle the buoyant force equals the weight of the liquid displaced, so a floating object always displaces liquid weighing as much as the object itself. Here only half the volume is inside the liquid, which tells us that half the object's volume of that liquid weighs as much as the whole object, so the object's density is half the density of the liquid. How much of the body stays under the surface depends on this density ratio, not on the size of the buoyant force. A is wrong because a liquid always pushes up on a body dipped in it. B is wrong because a smaller upward force would let the object sink further. C is wrong because a larger upward force would push the object up until less of it stayed submerged. Exam tip: floating means buoyant force = weight; fraction submerged = density of body ÷ density of liquid.

The correct answer is D, the statement that atmospheric pressure is negligible. Atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal, which presses with roughly the weight of one kilogram on every square centimetre of our body, so it is very large and not negligible at all. We do not feel it because the pressure of the blood and other fluids inside the body pushes outward with the same force, and the two balance. A is a correct statement because pressure is force divided by area, so the same force on a smaller area gives more pressure, which is why knives are sharpened and nails are pointed. B is correct because a liquid presses in every direction, on the bottom as well as on the side walls, and the push grows with depth. C is correct because the column of air above us has weight and therefore presses on us. Exam tip: P equals force divided by area; atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal.

The correct answer is C, increase in area of contact reduces pressure exerted. Pressure is the force acting on unit area, that is P equals F divided by A, so for the same force a larger area of contact means smaller pressure. The weight of the bag stays exactly the same whether the strap is thin or wide, but a wide strap spreads that weight over more of the shoulder, so the shoulder feels less pressure and the strap does not cut into the skin. The same idea explains why school bags, seat belts and the wide tyres of a tractor are made broad. A is wrong because it states the relation upside down, since pressure falls when area rises. B and D are wrong because the force is simply the weight of the load and the width of the strap cannot change it; only the pressure changes. Exam tip: P equals F divided by A, so broad straps and flat feet reduce pressure while sharp knives and pointed nails increase it.