Tài liệu luyện thi IBT

own or with object and adverbial, as a clause, can function as a subject. Example: To jump with a scale would be awkward (and dangerous). To conduct such a dangerous experiment requires great precautions. To-infinitive can function as a complement b. 1. As a complement after verb be Example: But a better way to describe their condition is to say they are in free fall His desire is to get success in his lifetime research. All I ask of you, the reader, is to keep an open, yet discerning mind. b. 2. As a complement after some adjectives Example: It is not easy to keep a car’s speed steady Even then, pointing to the one that’s harder to accelerate, you might from habit still say “That one is heavier” Here are some common adjectives in the pattern of the example one. ‘Good/bad’: marvelous, terrific, wonderful, perfect, great, good, nice, pleasant, lovely, terrible, awful, dreadful, horrible. Adjectives in –ing: interesting, exciting, depressing, confusing, embarrassing, amusing Difficulty, danger and expense: easy, difficult, hard, convenient, possible, impossible, safe, dangerous, cheap, expensive. Necessity: necessary, vital, essential, important, advisable, better/best Frequency: usual, normal, common, rare Comment: strange, odd, incredible, natural, understandable Personal qualities: good, nice, kind, helpful, mean, generous, intelligent, sensible, right, silly, stupid, foolish, careless, wrong, polite, rude Among those above adjectives, only those meaning ‘good’ or ‘bad’ and those of difficulty, danger, and expense can be used in the pattern of the example two. With many adjectives, you can use the pattern: It’s + adjective+ for somebody + to-infinitive Example: It’s important for you to complete all the observations before writing a report. It’s very expensive for a poor country to conduct a nuclear test. The following adjectives are used in this pattern: anxious awful better/best cheap convenient dangerous difficult eager easy essential expensive important keen marvelous necessary nice ready reluctant safe silly stupid terrible willing wonderful wrong We can use too and enough with a quantifier, adjective or adverb in the above patterns: Example: It is true that the flame of your alcohol burner is hot enough to produce the spectra of sodium, lithium, calcium, copper, and a few other elements, but that is not hot enough to produce the other spectra of elements, such as oxygen and chlorine. This bit of evidence was (much) enough to challenge Robert Bunsen, the German chemist, to search for a new element in the water. (there are two to-infinitive in this case, the former one is the complement, the latter one is the direct object for the first one, see c bellow ) It’s too dangerous for him to conduct such an experiment. b. 3. As a complement after some nouns Example: His determination to take a course in physics is very strong. It is one thing to recognize motion but another to describe it. Having no real reason to seek a better explanation than this for their observations, the team of medieval physicists unanimously concurred, and a new theory was born. Next, they found a smaller piece of glass and discovered that the suction cup had the gripping power to suspend it. Some nouns in this pattern are A to-infinitive can function as a direct object c.1. When a to-infinitive clause function as a direct object, it can have or have not a subject: Example: If we are curious about her speed at one certain time or at a point along the way, we want to know her instantaneous speed. The team of medieval physicists stepped out of the time machine and began to examine the strange, new device fastened to the window. This new revelation prompted another physicist to remark, "The device must also attract the glass!" (In this case the subject of the to-infinitive is another physicist) I merely wish to emphasize mankind's present level of ignorance of the mechanics of our universe. The spectroscope thus enables us to distinguish one element from another. (the subject of the to-infinitive clause is implied in us) Here are the common verbs that take to-infinitive as direct object afford (have enough time/money) agree aim arrange ask attempt beg can’t wait train choose claim dare decide demand expect get(=succeed) guarantee hasten undertake have help hesitate hope learn long manage neglect offer used (to) omit ought plan prepare promise refuse seek swear threaten wish c.2. You can see that all the above verbs are intransitive verbs. There are some verbs which are not intransitive but still followed by to-infinitive. These verbs include: seem, appear, happen, tend, come, grow, turn out and prove. Example: This lack of movement might seem to be strangest of all, for we humans are used to motion. The difference in pressure cause, what appears to be, an attraction. While in free fall, things seem to have no weight relative to each other. In these cases, the to-infinitive say something about the truth of the statement, or the manner or time of the action. In some cases, empty it can be used as the subject-It seems that he has got success in his research. To-infinitive can follow question word/phrase to form an objective clause (refer to Grammar in Use-UNIT six) Example: Please make sure when to start the observations. We should know how high the temperature to be kept for the substance to react completely in the reaction. Here are the verbs that can take the question word to follow advise someone ask someone choose consider decide discover discuss explain find out forget know learn remember show someone teach someone tell someone think understand wonder work out A to-infinitive clause can express purpose and result Example: Purpose: To describe motion accurately, we use rates. It takes accurate measurements of the positions of spectral lines to identify an element. We can use this fact and the formula Fnet = ma to find the weight of an object To measure your weight you can use a bathroom scale Result: (this way of expressing is unusual) He made so many observations only to find that he was unsuccessful. A to-infinitive can replace a relative clause: e. 1. A to-infinitive can follow a ordinal number to replace a relative clause Example: Galileo Galilei (1564-1642) was the first to understand how earth’s gravity affects things near the surface of our planet. Lomonosov was the first to experimentally prove the constancy of the mass of matter participating in chemical transformations. e.2. A to-infinitive is placed after a noun/pronoun to replace a relative clause Example: Even mosses and lichens that spend their lives fastened to rocks depend on the movements of gases and liquids to bring them the chemicals essential to life and to carry others away. (meaning which bring them… and carry…) Note: This way of expression is not really common. Patterns for bare infinitive: 1. Bare infinitive goes after modal verbs and some special phrases Example: If a body is at rest, it will remain at rest. The glass must attract the device. The device must also attract the glass. f..2. Pattern: verb+ object+ bare infinitive The common verbs in this pattern are make, let, and have (meaning cause) and those of perception. Example: You know that things will fall if you let them go off your hands. In a solar eclipse, with your unaided eyes, you can not see the Moon cover the Sun. Practice Exercise 1: Choose the correct infinitive form of the verbs given in parentheses. Give your explanation For the interference pattern (appear)……………….. on viewing screen C, the light waves reaching any point P on the screen must have a phase differences that does not vary in time. If you look closely at your fingernail in bright sunlight, you can see a faint interference pattern called speckle that causes the nail (appear)…………….. covered with specks. You see this effect because light waves scattering from very close points on the nail are coherent enough (interfere)……………… with one another at your eye. (get)…………….. coherent light, we have to send the sunlight through a single slit; because that single slit is small, the light that passes through it is coherent. The equations – d sin θ = mλ, for m= 0, 1, 2… and d sin θ = (m+1/2) λ, for m =0, 1,2… tell us (locate) …………….. the maxima and minima of the double-slit interference pattern on screen C as a function of the angle θ presented in the figure. Here we wish (derive) …………….. an expression for the intensity I of the fringes as a function of θ. (combine) …………….. the field components E1 and E2 on a phasor diagram, we add them vectorially. If you sight through a pinhole in an otherwise opaque sheet so as to make the light entering your eye approximately a plane wave, you might be able (distinguish) …………….. individual maxima and minima in the pattern. To locate the fringes, we shall use a procedure somewhat similar to the one we used (locate) …………….. the fringes in a two-slit interference pattern. The fact that lens images are diffraction patterns is important when we wish (resolve) …………….. two distant point objects whose angular separation is small. When we wish to use a lens (resolve) …………….. objects of small angular separation, it is desirable (make…………….. the diffraction pattern as small as possible. A grating’ capability (resolve) …………….. separate lines of different wavelengths depends on the width of the lines. Interference coatings can also be used (enhance) …………….. – rather than reduce- the ability of a surface to reflect light. To understand interference, we must (go)…………….. beyond the restrictions of geometrical optics and employ the full power of wave optics. In fact, as you will see, the existence of interference phenomena is perhaps our most convincing evidence that light is a wave- because interference can not (explain) …………….. other than with waves. The first person (advance) …………….. a convincing wave theory for light was Dutch physicist Christian Huygens, in 1678. His wave theory is based on a geometrical construction that allows us (tell) …………….. where a given wave- front will be at anytime in the future if we know its present position. If we actually try to form a ray by sending light through a narrow slit or through a series of a narrow slits, diffraction will always defeat our effort because it always causes the light (spread) ……………... It’s quite a surprise (find) that there are situations where electrons appear (behave) …………….. like waves. This is just what is observed when a beam of energetic electron is used instead of a beam of light in a double-slit experiment. Another even more surprising result is found when we make the electron beam sufficiently weak that there is never more than one electron in the beam at a time from the electron gun. We still get a pattern of interference fringes. Each single electron seems (pass) …………….. as a wave through both slits, and then recombined on the other side to give a single flash at the screen. Physicists found it hard (explain) …………….. why weak ultraviolet light could have an immediate effect on the electrons in the metal, but very bright light of lower frequency had no effect. Metals (such as zinc) …………….. have electrons that are not very tightly held within the metal. These are the conduction electrons, and they are free (move) …………….. about within the metal. When photons of light strike the metal, some electrons break free. They only need a small amount of energy -about 10-19 J- (escape) …………….. from the metal. Now we can see the photon of light (work) …………….. because it pictures light as concentrated particles of energy, each one able to release an electron from the metal. White light consists of photons of many different energies. For a photon (absorb)…………….., it must have exactly the right energy to lift an electron from one energy level to another. First we should remind ourselves that waves and particles are macroscopic phenomena. We are using these models (describe) …………….. microscopic phenomena, and we should not be surprised that they do not work perfectly. But it is still difficult (explain) …………….. why one model works well in one situation, and the other in another situation. We should (not try, imagine) …………….. …………….. “waves of matter” or “particulate waves”; these do not give a true representation of what we observe. However, we can (make) things more acceptable by giving rules, which tell us when (use) …………….. the particle model and when (use) …………….. the wave model. Then, at least, we can solve problems, which is what we really require of physics. The gerund Gerund forms A gerund is formed exactly like a present participle form of a verb (i.e. simply by adding –ing to the end of the verb) as follows: Active Passive Simple conducting being conducted Perfect having conducted having been conducted Implications of the gerund A simple gerund refers to something happening at the same time as the action in the main clause Example: Conducting such an experiment is very dangerous. (In this case the action of conducting is at the same time with the being dangerous) A perfect gerund refers to something happening earlier than the action in the main clause Example: He made the report without having made enough observations. (the action of not making observation happens before the action of making report) It’s unnecessary to use a perfect if it is clear from the context that the time of the gerund is earlier than the time of the action in the main clause: The above example can be rewritten in this way: He made the report without making enough observation. (Everyone knows that to make a report, before that enough observations must be made for the sake of scientific accuracy) To form a negative we simply add the negative word ‘not’ before the gerund Example: He’s afraid of not being able to complete his thesis. Gerund clause A gerund on its own or can be combined with other elements (with subject; object; or adverbial) to form a clause: Examples: conducting such an experiment not being able to complete his thesis having made enough observations Functions of the gerund A gerund can be treated as a noun/noun phrase, so it has a wide range of uses as a noun/noun phrase A gerund can be treated as a noun on its own or can be used to modify another noun Example: Neighboring molecules beneath them are set into faster motion, and heat flows into the floor. This is called the microwave background, and is the remnant of radiation from the ‘big bang’, the giant explosion that is believed to have occurred at the beginning of time in the Universe. Perhaps nothing is so ingrained in our senses as the perpetual pulling of the earth on our surroundings. The physical meaning of this new concept – mass- is related in the most intimate way to the identity in comparing weights which we have just noted. It’s just that nothing would stop that fall, there would be no supporting force opposing the gravitational pull, so he would feel weightless. As a subject of a sentence Example: Sitting and observing a substance to decay is a hard work. Finding the cause of the earth’s field has taken much time of the scientists throughout the story. When functioning as the subject of a sentence, a gerund can be replaced by a to-infinitive, but there is a difference between them. While a gerund refers to something in general, a to-infinitive refers to something in a particular situation. As a complement after be Example: What he has to do now is quickly finishing his research. As a prepositional complement d.1. As a complement after a preposition following a noun Example: The question of finding the cause of the earth’s magnetic field has drawn a great attention from physicists. We can not see electric current in a wire, so we find different ways of explaining what is going on. The following nouns with their prepositions can be followed by a gerund advantage of aim of/in amazement at anger about/at annoyance about/at anxiety about apology for awareness of belief in boredom with danger of/in difficulty (in) effect of excitement about/at expense of/in fear of insistence on interest in job of matter of objection to pleasure in/of point of/in possibility of problem in/of worry about prospect of purpose of/in question about/of reason for satisfaction with success in surprise at task of work of As a complement after a preposition following an adjective Example: This internal energy spreads out, making it much less effective at producing work than, say, the organized kinetic energy of a moving object. Energy has been called the “common denominator” of the natural science because its conservation law makes it so useful in understanding any physical process. The following are the adjectives with their prepositions that can take a gerund afraid of amazed at angry about/ at annoyed about/at anxious abut ashamed of aware of bad at bored with capable of content with dependent on different from/to excited about famous for fed up with fond of good at grateful for guilty of happy about/with interested in keen on nervous of pleased about/with ready for responsible for satisfied with sorry about/for successful in surprised at worried about wrong with Other prepositions that are followed by a gerund after against as a result as well as because of before besides by by means of despite for how about in in addition to in favor of in spite of instead of on on account of since through what about with without Example: Absorption spectra of gases may be obtained by passing white light through a sample of gas before the light enters the prism. By measuring the magnetic orientation and determining the age of such rocks, scientists can measure the orientation of the earth’s magnetic field at different times in the earth’s history. Using springs of various thickness, one can make scales for measuring very large and also very small weights. As a complement after adjectives expressing degrees of difficulty Example: It’s difficult detecting an element without using a spectroscope. It’s impossible keeping a car in steady speed. Note: Refer to the Grammar in use part in UNIT ELEVEN for these adjectives. However, It’ is more common to use a to-infinitive instead of a gerund. As a direct object after some verbs These verbs include some one - word verbs and some prepositional verbs Example: We can live quite happily without thinking about why this is so. Once we start thinking about the force of gravity, which makes things fall, we may come up with some odd ideas. He’s thinking of taking a course of physics. Some energy goes into raising the temperature of the cylinder walls and the piston, and that part spreads outward, doing no useful work The following verbs take gerund as a direct object admit advise allow anticipate appreciate avoid can’t help confess consider delay deny detest dislike enjoy escape excuse face finish give up imagine involve justify keep (on) leave off mention mind miss permit postpone practice put off quit recommend resist resume risk save suggest tolerate The following prepositional verbs can take a gerund admit to (dis)agree with aim at apologize for (dis)approve of believe in benefit from care for confess to count on depend on feel like get on with insist on object to pay for put up with rely on resort to succeed in think of vote for Note: Of all the adjectives, nouns, and verbs listed, many may not be used frequently in a document of purely scientific matter (with technical sense only). However, if you have a chance to get access to wider range of reading materials (especially those about our universe and human beings, which are viewed in many aspects of physics), you can find them with more frequent use. Practice Exercise 1: Complete the sentences with the correct form of the verbs given: to-infinitive or gerund or present participle. State each case of a gerundthat is used. You can use your knowledge of how charged particles and electric currents are affected by fields (interpret) ……………… diagrams of (move) ……………… particles. You can use such an arrangement (observe) ……………… the effect of (change) ……………… the strength and direction of the field, and the effect of (reverse) ……………… the field. Note that you can seriously damage a television set by (bring) ……………… a magnet close to the screen. You can make a field in two ways: (use) ……………… a permanent magnet, or (use) ……………… an electric current. There is really no fundamental difference between these two ways of (create) ……………… magnetic fields. You should be familiar with the magnetic field patterns of bar magnets. These can be shown up (use) ……………… iron bar fillings or (plot) ……………… compass. We represent magnetic fields, like gravitational and electric fields, by (draw) ……………… lines of force. In a solenoid, (reverse) ……………… the current reverses the direction of the field. Here are some useful rules for (remember) ……………… the direction of the magnetic field produced by a current: The right- hand grip rule gives direction of field lines in an electromagnet. Imagine (grip) ……………… the coil, so that your fingers go around it (follow) ……………… the direction of the current. Your thumb now points in the direction of the field lines inside the coil, i.e. points towards the electromagnet’s north pole. The corkscrew rule is a way of (remember) ……………… the direction of the field lines around a current- carrying wire. Imagine (push) ……………… a corkscrew into a cork, and (turn) ……………… it. The direction in which you push is the direction of the current, and the field lines go round the direction in which you are turning the corkscrew. The magnet creates a fairly uniform magnetic field. The rod has a current (flow) ……………… through it. As soon as the current is switched on, the rod start (roll) ………………, (show) ……………… that a force is acting on it. We use Fleming’s left-hand rule (predict) ……………… the direction of the force. There are three things here, all of which are mutually at right-angles to each other – the magnetic field, the current in the rod and the force on the rod. These can be represented by (hold) ……………… the thumb and first two fingers of your left hand so that they are mutually at right-angles. Your fingers then represent: thuMb-Motion; First finger- Field; seCond finger-Current. You should practice (use) ……………… your left hand (check) ……………… that the rule correctly predicts these directions. Scientists have put considerable effort into (research) ……………… for particles that have just one magnetic pole (magnetic monopoles). We can generate electricity by (spin) ……………… a coil in a magnetic field. This is equivalent to (use) ……………… an electric motor backwards. Another use of electromagnetic induction is in transformers. An (alternate) ……………… current in the primary coil produces a (vary) ……………… magnetic field in the core. The secondary coil is also wound round this core, so the flux (link) ……………… the secondary coil is constantly changing. Hence a (vary) ……………… e.m.f. is induced across the secondary. Ampere’s (find) ……………… revealed that when a charged particle crosses magnetic lines, it gets pushed to one side. The tendency of a compass needle (dip) ……………… is a nuisance for compass users. (eliminate) ……………… this motion in a compass made for use in North America, the needle is suspended off center, or even counterweighted on the southern end, so that it moves only in the horizontal plane of the compass. Electromagnets are the (work) ……………… parts of some of the instruments used (measure) ……………… currents and voltages. In 1681, an English ship (sail) ……………… to Boston was struck by lighting. After the storm had passed, the sailors noticed that the ship’s compass no longer pointed north. Somehow, the lighting had reserved the magnetic poles. Nevertheless, (use)……………… the wrong end of the compass for orientation, they came safely into Boston Harbor. A person moves by (push) ……………… off from the Earth; a boat sails because the rowers push against the water with their oars; Thus, (push)………. off from a support seems (be) ……………… a necessary condition for motion; even an airplane moves by (push) ……………… the air with its propeller. But is it really? Might there not be some intricate means of moving without (push) ……………… off from anything. If you rub a strip of plastic so that it becomes charged, and then hold it close to your hair, you feel your hair (pull)……………… upwards. Noun clause (3) Hereby, noun clauses forming with whether….. or not and if, sometimes known as yes-no interrogative clause are presented. In two conjunctions, the former one is a correlative subordinator while the latter one is a simple subordinator. The noun clauses formed from these two subordinators have the following functions in a sentence: Both can function as a direct object Example: On a straight and smooth road, we can not feel whether there is any change in your car’s speed. To find out if temperature has any effect on the intensity of radiation from radioactive substances, samples of these substances have been heated to very high temperatures, and they have been cooled to very low temperatures in liquid air. Whether can take a to-infinitive after it Example: 1. He did not know whether to go on with the research (or not). Only the clause with whether can function as a subject Example: Whether a solid is crystalline or amorphous depends on how it is formed. Note that only whether can be followed by ‘or not’ but the clause with it can not be made negative, except when it is the second part of an alternative question. Example: When analyzing a change in matter, we should clarify whether it has undergone a physical change or (it has) not. Note: ‘Whether’ is more commonly used than ‘if’. That’s why you’ll encounter a lot of ‘whether’ to be used rather than ‘if’. You may have seen that a noun clause with ‘whether’ or ‘if’ somehow originates from a yes/no question because it leaves only two choices for the answer. Still, the question is used for a confirmation of the information by ‘yes’ or ‘no’, a ‘whether’- clause leaves a wonder for the information by ‘or not’. Patterns expressing result It is really important that you know how to state a result of an action, especially when you write a description or/and make a report. You have learnt how to use a to-infinitive to express result though uncommonly, and you did learn in UNIT TEN that a present participle phrase can also be used to express result. Some common conjunctions or conjunctional phrases, which are commonly used to do such a task, will be presented. A lot of conjunctions/connectives can be used: so; therefore; thus (V-ing); hence (V-ing); accordingly; consequently; now; then; so that. Besides, there are some conjunctional/connective phrases to be used in this way: with the result that; as a result/consequence; the result/consequence is; for this/that reason; because of this/that Example: In 1905, Einstein showed that as a consequence of his theory of special relativity, mass can be considered to be another form of energy. Thus the law of conservation of energy is really the law of conservation of mass-energy. A mass has zero gravitational potential energy when it is ‘at infinity’- that is, at some point so far from the Earth and any other massive objects that it feels no gravitational force. Then, to calculate the potential energy of a mass near to the Earth (or anywhere else), we calculate the work done against gravity in bringing the mass from infinity to that point…Hence, we can arrive at the following definition: The gravitational potential at a point in a field is equal to the work done against gravity in bringing unit mass from infinity to that point. So The frequency of vibration is set so that there are two loops along the string; the frequency of the stroboscope is set so that it almost touches that of vibration. A ball thrown horizontally in the Earth’s uniform gravitational field continues to move at steady speed horizontally, but at the same time it accelerates downwards. The result is the familiar curve is shown. The diagram shows that the electrons will be pushed in the direction from X to Y. So a current has been induced to flow in the wire; its direction is from Y to X. Practice Exercise 1: Find a sentence in column B to match with each one in A to make a pair of sentences which are closely related in meaning. A B The smallest divisions on a metric ruler are 0.1cm (1mm) apart; this is a small distance indeed. If the edge of the measured object falls between two lines of 4.8 and 4.9 cm, to gain more information, you have to estimate the position of the edge. Think of two glasses containing liquids, both liquids are transparent and have no smell. If we want to find out whether two objects are made of the same substances or of different ones, we have to look for properties that are characteristic of a substance. The density of the liquid in a car’s radiator tells us whether there is enough antifreeze (in most cases, glycol) in the mixture. To find the concentration of a saturated solution, you could add a tiny amount of solid at a time and see whether it dissolves. To find out whether temperature has any effect on the intensity of radiation from radioactive substances, samples of these substances have been heated to very high temperatures, and they have been cooled to very low temperatures in liquid air. If we ignore air resistance, the total external force acting on the system is the weight Mg of the system, regardless of whether the rocket explodes. We think of this cutting of flux by a conductor as the effect that gives rise to an induced current flowing in the conductor. Isaac Newton investigated the question of the Earth’s gravity. Because almost everything you do requires moving something about, whether you’re turning a page or merely taking a breath, you know all this ahead of time. Suppose we have a newly made substance. If an isolated conductor is placed in an external electric field, all points of the conductor still come to a single potential regardless of whether the conductor has an excess charge. Regardless of whether they have permanent electric dipole moments, molecules acquire dipole moments by induction when placed in an external field. Sometimes we wonder whether it is necessary to turn to a graph to find the magnitude of the displacement of a point making small oscillation about its equilibrium position. A better method is to begin with a large mass of solid and shake it until you judge that no more will dissolve. But it was found that temperature changes do not affect the radiation from a radioactive substance. Can you say whether they are the same? If you can not tell whether the edge is closer to one line or the other, it is best to report the reading as 4.85 cm or 48.5 mm. In particular, he wondered whether the Earth’s gravitational pull was confined to the Earth’s surface, or whether it extended into space – as far as the Moon. It does not matter whether the conductor is moved through the field, or the magnet is moved past the conductor, the result is the same – an induced current flows. It’s no, because theory shows that in this case the curve depicting the dependence of the displacement on the time is a sinusoid. Nevertheless, when the object you wish to measure has sharp edges, you can see whether the edge fall s on one of the lines. Similarly, the density of the liquid in a car’s battery should be recharged. That is, we have to find out the properties that do not depend on the amount of the substance or on the shape of the sample. That is, you have a feeling that is based on experience for how things move. The free conduction electrons distribute themselves on the surface in such a way that the electric field they produce at interior points cancels the external electric field that would otherwise be there. This external field tends to ‘stretch’ the molecule, separating slightly the centers of negative and positive charge. Thus, the acceleration of the center of mass of the fragments (while they are in flight) remains equal to g, and the center of mass of the fragments follows the same parabolic trajectory that the unexploded rocket would have followed. We wish to find out whether it is truly a new substance, different from all others, or a substance already known but made in a new way. Exercise 2: Fill in each blank with one suitable word. Some of the words are those listed in grammar part B. Electromagnetic induction. So far, we have not given an explanation of electromagnetic induction. You have seen that it (1) ……………occur, and you know the factors that affect it. But why does an induced current flow? The following will give a(n) (2) …………….. A straight wire XY is being pushed downwards through a horizontal magnetic field B. Now, think about the free electrons (3) ……………. the wire. They are moving downwards, (4) ……………in effect an electric current. Of course, because (5)……………….are negatively charged, the conventional current is flowing upwards. We (6) ……………. have a current flowing across a magnetic field, and the motor effect will (7) ……………..come into play. Using Fleming’s left-hand rule, we can find the direction of the force (8) ……………. the electrons. The diagram shows that the electrons will be pushed in the direction from X to Y. So a current has been induced to flow in the wire; its direction is from Y to X. Now we can check that Fleming’s right- hand rule gives the correct direction for motion, field and current, which it indeed does. (9) ……………., to summarize, an induced current flows because the electrons are pushed by the motor effect. Electromagnetic induction is simply a (10) ……………. of the motor effect. Matter and temperature. If we heat some matter so that its temperature rises, the amount of energy we must (1). ……………..depends on three things: the mass m of the material we are (2) ……………...; the temperature rise rϑ we wish to achieve (r is Greek capital delta); and the material itself. Some materials are easier to heat than others – it takes more energy to raise the temperature of 1 kg of water by 10C than to raise the temperature of 1 kg of alcohol by the (3) ……………...amount. We can represent this in an equation. The amount of energy rQ that must be supplied is given by: rQ = mcrϑ (4) ………………..c is the specific heat capacity of the material. Rearranging this equation gives c = rQ/mrϑ.(5) ………………….,the specific heat capacity of a substance is the amount of energy required to raise the (6) ……………..of 1 kg of the substance by 10C (or by 1K). (The word ‘specific’ here means ‘per unit mass’, i.e. per kg). (7) ……………..this form of equation, you should be able to see that the units of c are Jkg-1 0C-1 (or Jkg1 K-1 ). Specific (8) ……………...capacity is related to the gradient of the sloping sections of the time-graph for water, heated at a steady rate. The steeper the gradient, the faster the substance heats up, and (9) ……………. the lower its specific heat capacity must (10) ……………. Metals. The feature that defines a metal is that, the highest occupied energy level falls somewhere near the middle of an energy band. If we (1) ……………. a potential difference across a sample of such a solid, a current can exist because there are plenty of vacant levels at higher energies into (2) ……………....electrons can be raised. (3) ……………..a metal can conduct electricity because electrons in its highest occupied band can easily move into higher energy levels within (4) …………….. band. We did mention the free-electron model of a metal, in which the conduction electrons are (5) …………….. to move through the volume of the (6) ……………... like the molecules of a gas in a closed container. We used this model to derive an expression for the resistivity of a (7) ……………..., assuming that the electrons follow the laws of Newtonian mechanics. Here we use that same (8). to explain the behavior of the electrons – called the conduction electrons. However, we (9) …………….the laws of quantum mechanics by assuming the energies of these electrons to be quantized and the Pauli Exclusion Principle to hold. We (10)……………. too that the electric potential energy of a conduction electron has the same constant value all points within the lattice. If we choose this value of the potential energy to be zero, as we are free to do, then the energy E of the conduction electrons is entirely kinetic. A review of prepositions As a review on prepositions, the following just gives a summary on what types of prepositions there are, basing on the function of each. First we should go through briefly about prepositions in general A preposition usually comes before a noun phrase, sometimes an adverb Example: in our minds into a model through a bulb at once up to now through there Prepositions and their object to form a prepositional phrase functioning as an adverbial Example: We all live on terra firma, the 29 percent of our planet’s solid crust that lies above sea level. Rubber bands, books, and the clothes you wear- these flexible materials maintain their shape to some degree. We’ve seen that at the atomic level, the atoms or molecules bonded together in a solid stay in place with respect to their neighbors. Some prepositions can also be adverbs, many forming phrasal verbs Example: Whether a solid is crystalline or amorphous depends on how it is formed. Especially, slow cooling can sometimes results in very large crystals. Some prepositions of time can also be conjunctions Example: After preparing carefully, he successfully detected the questionable element in the compound. He had made lots of observations before he made such a report. Types of prepositions Prepositions of place: In/inside on/ on top of under(neath) above/over under/below up/down through off out of at next to/by/beside close to/near in front of behind between opposite among round beyond against Example: To understand interference, we must go beyond the restrictions of geometrical optics and employ the full power of wave optics. Prepositions of direction/movement: onto into to away from from along past towards across around through off Example: Toss your keys along the floor, they’ll skitter along for a bit as friction does negative work on them, reducing their kinetic. Prepositions of time: at on in during over since/for till/until before/ after by from between Example: But we can be quite sure that the temperature and pressure of the hydrogen are nearly the same all over the classroom for a short time. Prepositions with other meanings about according to against as/as for for by instead of because of with respect to on on behalf of up to with of Example: We can choose any convenient volume of hydrogen in a test tube as our unit of electric charge. Idiomatic phrases with prepositions at top speed from……..point of view by mistake in advance out of order at risk on average Example: The equipment is out of order now, you should call for an engineer. Practice Exercise 1: Fill in the blank with suitable prepositions You will be familiar (1).............the idea that, when you use a power supply or other source (2)............e.m.f., you can not assume that it is providing you (3)............ the exact voltage that its controls suggest. You need to measure the voltage to be sure (4).............its value. There are two reasons (5)............this. First, the supply may not be made (6)............a high degree of precision, batteries become flat, and so on. However, there is a second, more important, reason for measuring the voltage (7)................the supply to be sure of its value. Experiments show that the supply voltage depends (8)............the circuit of which it is part. (9)..............particular, the voltage of a supply decreases if it is required to supply more current. Matter is made up (1).............three types of particles: electrons (which have negative charge), protons (positive) and neutrons (neutral). An uncharged object has equal numbers (2).............protons and electrons, whose charges therefore cancel out. When one material is rubbed (3)..............another, there is a force of friction (4).............them, and electrons may be rubbed off one material (5).............the other. The material that has gained electrons is now negatively charged, and the other material is positively charged. If a positively charged object is brought close (6)..............an uncharged one, the electrons (7)..............the second object may be attracted; we observed this (8)………..a force of attraction between two objects. (This is electrostatic induction) Note that it is usually electrons that are involved (9).............. moving within a material, or (10)............one material to another. This is because electrons, which are (11)............the outside of atoms, are less strongly held within a material than protons; they may be free to move about within a material (like the conduction electrons in a metal), or they may be relatively weakly bound within atoms. Exercise 2: Complete each of the following statements with suitable phrases from the list given A. between two parallel metal plates I. on each other B. between them C. by showing lines of forces J. spreads outwards in all directions D. due to an excess of electrons. K. with the addition of a small amount of energy E. in moving from one plate to the other. M. to that point F. In order to observe the field N. being pulled upwards G. once summoned by friction O. to some degree H. to leak away into the air P. in the process of doing work ........................, we need to put something in it that will respond to the field. If you rub a strip of plastic so that it becomes charged and then hold it close to your hair, you feel your hair …………............. We can draw electric fields in much the same way that we can draw gravitational and magnetic fields................................ A radial field....................., for example from a point charge or from a charged sphere. You can set up a uniform field ........................... by connecting them to the terminals of high- voltage power supply. Any two charges particles exert a force ........................that is proportional to each of their charges and inversely proportional to the square of the distance between them. It is quite tricky to investigate the force between charged particles, because charge tends ........................during the course of any experiment. ........................., energy is transferred from you to the charge that you are pushing. The potential difference (voltage) between the plates tells us the energy charge per coulomb......................... The electric potential at a point is equal to the work done per unit charge in moving a positive charge from infinity.......................... Long before the days of plastic pens and rubber balloons, investigators found that charges, …........................., could be transferred from one material to another. To day, we know that any material can become charged ............................by bringing it into contact with a different material. The negative charge on a piece of rubbed amber or rubber is............................... A semi-conductor is an electrical insulator that, ....................................., becomes a conductor. A proton repels another proton and attracts any electron, though nothing tangible bridges the distance.................................... Some confusing pairs of conjunctions In English there are some pairs of conjunctions that are interchangeable in a sentence. This means, we can use either of the two to form the sentence while the meaning of the other is also implied. In Vietnamese, you have to use both of them if you want to build the equivalent sentence. The following two are the common ones. but and (al)though Example: You can write: Although uranium was formed at the same time as the formation of the earth, it is not the main part of the earth. (Uranium is not the main part of the earth (al) though formed at the same time as the formation of the earth) Or: Uranium was formed at the same time as the formation of the earth, but it is not the main part of the earth. You can not write: Though uranium was formed at the same time as the formation of the earth, but it is not the main part of the earth. In this case, if you replace but with still or yet, you may have the sentence that sounds like your Vietnamese way of expression. because and so Example: You can write: Because uranium has the heaviest nuclei, it is used in fission reaction. Or: Uranium has heaviest nuclei, so it is used in fission reaction. Adverbs with two forms In English there are a number of adverbs that have two forms, which are quite different in meaning when functioning in many contexts. Example: hard and hardly In this case: He has work hard but hardly reached the goal. With: Hard: strenuously and industriously (showing the manner of the action) Hardly: almost never You have more pairs: rough: in the open air, or outside roughly: violently, briefly, or approximately flat: level and horizontal flatly: frankly free: without freely: liberally late: after the usual or normal time lately: recently wide: large and broad in size widely:broadly, generally near: close to nearly: almost Practice Exercise 1: Combine each of following pairs of sentences to one sentence, using appropriate conjunctions. The rock formations of Grandfather Mountain in North California are 1 billion years old. The oldest rocks on earth- some 4 billion years old-lie in Green land. …………………………………………………………………………………...…………………………………………………………………………………... Plants use carbon dioxide from the atmosphere (and emit oxygen) in their life processes. Any living plant has the same ratio of carbon -12 to carbon-14 atoms as the atmosphere does at that time. …………………………………………………………………………………..…………………………………………………………………………………..………………………………………………………………………………….. All animals (including humans) depend on plants through the food chain. They have carbon-12 and carbon -14 in this same ratio. …………………………………………………………………………………..…………………………………………………………………………………... In 1932, two of “papa” Rutherford’s “boys” John Cockroft and Earnest Walton, managed to build a device to accelerate protons. It produced only 100.000 volts or so. …………………………………………………………………………………...…………………………………………………………………………………... The arrangement of electrons to make the bonds releases 4.1 electron volts energy. The splitting (or fission) of one uranium atom’s nucleus would release some 2000 million electrons volt of energy. …………………………………………………………………………………..…………………………………………………………………………………..….……………………………………………………………………………….. Uranium-235 nucleus fissions most easily by absorbing a slow neutron. It can also fission (with a lower probability) as a result of a strike by a fast neutron. …………………………………………………………………………………..………………………………………………………………………………...... Liquid metal sodium boils at 8950 C. It does not have to be under high pressure as water does. …………………………………………………………………………………...…………………………………………………………………………………... The liquid sodium also becomes very radioactive because its nuclei can capture neutrons. It is much less efficient than water radiation. ………………………………………………………………………………...……………………………………………………………………………………... Fission reactions are controlled today in nuclear power plants. Fusion reactions have yet to be tamed. …………………………………………………………………………………...…………………………………………………………………………………... The binding energy per nucleon is different among the various nuclei. The arrangement of the nucleus by either breaking the nucleus apart or by merging nuclei together always releases or absorbs energy. ………………………………………………………………………………...…………………………………………………………………………………...……………………………………………………………………………………... Exercise 2: Complete the following statements by filling in each gap with one suitable adverb presented in Grammar in use B Over the last 1,000 years the science of physics has enabled us to probe and understand the world of the very large—the stars and the galaxies that contain them—and, ..........................., the world of the very small—the fundamental particles that make up matter and the forces that govern their interactions. Scientists are now working ………………. to solve the problem of worldwide energy crisis. Though entering the forum of particle physics ………………., he has made himself ……………… well-known with an astonishing assumption about elementary particles. The forum is always open ………….. for such a figure. Though not refusing…………….. Newton’s theory that light behaves as particles; Young draw attention of scientists at his time all to his new theory that light behaves as a wave. Electrons are the …………..- moving particles in an atom. Before going on with the details of the report, he presented the content ……………. with an Overhead Projector, getting his audience all ears to him. He intended to do his experiment ……………… but his supervisor disagreed because he insisted that the experiment must be conducted in room temperature. He ..................... reached the goal when he decided to quit the research only because of financial deficiency. While lying ……………. on the floor, he suddenly found out the solution to what he is wondering. If the north pole of a magnet is brought ………….. the south pole of another, the poles will attract each other. 6.