Abstract: Almost everyone will have seen a micrograph which is scanned in synchronism with the primary produced by a scanning electron microscope. These electron beam. Secondary electrons are detected and dramatic photographs make microscopic animals used to form the display which results in the dramatic, appear as monsters in popular scientific books and high depth of field images with which we are familiar. programmes, showing that the scanning The

Abstract: To an observer who has a clear and unobstructed view of the distant horizon the setting of the sun is one of the most fascinating phenomena that can be seen in nature. The shapes and the colours of the disc of the setting sun are both beautiful and surprising, and they can be explained in terms of refraction. scattering and dispersion of light in the atmosphere. Teachers may therefore be able to explain and illustrate these topics of physics with the help of sunset phenomena. Linked classroom experiments on atmospheric refraction and scattering have been described elsewhere (e.g. Trowbridge 1973. Kruglak 1973, Johnston 1977). Although my comments in this article relate to the setting sun, they apply equally well to the rising sun. I shall deal with normal sunset phenomena, sunsets over warm land or water and the characteristics of sunsets that occur when there is a layer in the

Abstract: In their contribution to the ‘nuclear debate’ in the September issue of Physics Education (1981 16 274-81), H I Ellington and E Addinall seem to prefer the arguments that are now familiar to readers of the glossy publications of the CEGB and the nuclear industry. The main thrust of these is that energy consumption must increase to fuel our growthorientated society and that this energy must be mainly nuclear-produced electricity. Views which challenge these assumptions are represented in the bibliography to heir a ticle, but the authors’ discussion of the opposition views is limited. They thus dodge the central issue: if we can continue to expand our centralised high technology society whose built-in wastefulness demands such prodigious energy inputs, then who does this really benefit? The nuclear debate is more about political than technical choices. G Kneale (1981 16 284-6) discusses the apparently technical question of health hazards and concludes ‘Clearly at this stage we must leave the final decision to responsible politicians’. Unfortunately experience suggests that political responsibility is biased by external pressures. A prime example is the lead in petrol issue. Recently British politicians have been seen congratulating themselves for finally complying with EEC regulations and reducing the lead in petrol to 0.15 g l ” by 1985. This pathetic half-measure, in the face of well attested evidence of brain damage to children from airborne lead, avoids inconvenience to the UK motor and oil industries and has been bolstered by ‘the demonstrably false yet largely unchallenged claims by ministers that most cars on the road would not run on lead-free petrol’ (The Guardian 1 October 1981). The history of the use of nuclear energy in the UK suggests that similar pressure from industrial lobbies operates. I hope that participants in the ‘nuclear debate’ will explore this. Perhaps, as the reference quoted on p282 suggests, ‘nuclear power represents an unfortunate technological cul-de-sac’, which may prove to be as irrelevant to real human needs as the pyramids and the vast concrete bunkers proposed for the MX missiles. R WHowes Camberiey, Surrey

Abstract: And now we do turn to a discussion of the laws of thermodynamics, which will provide a further framework for the study of chemical systems. We will approach these laws using a semihistorical perspective. Not because we are interested in the history of the development of these laws, however interesting it may be, but because this provides us with an easy and conceptual picture of their scope and enunciation. As we do this, we will move pretty far afield from chemistry. We must keep in mind that our discussion will eventually lead us back to theories concerning the physical properties of chemical substances. And these theories will be framed within the framework of thermodynamics. Atkins says this rather grandly:

Abstract: References Ausubel D P and Robinson F G 1969 School of Learning-an Introduction to Educational Psychology (New York: Holt, Reinhart and Winston) Ebers J J and Moll J L 1954 'Large-signal behaviour of junction transistors' Proc. IRE 42 1761-72 Waks S and Silberstein I 1978 'Integration of theory and laboratory experimentation in self-instructional electronics courses' B. J . Educ. Technol. 9 May

Abstract: into some of the local schools I must consider the question, Where do we go from here? The concept of schools using visiting lecturers from further and higher education has precedents and is of value if the lecturer has spent some years in schools as well as knowing the subject. The ideal, I suggest, would be a peripatetic teaching system-efficient as regards utilisation of all kinds of resource. Such an astronomical teaching facility is described in the second inset; it would embrace and link all astronomical interests in the area concerned.

Abstract: Physical models, like a train set, an aircraft model in a wind tunnel or even a statue of Venus, all aim at portraying certain attributes of life. Mathematical models, too, aim at representing aspects of reality but in a more abstract form. This is the first part of an article about mathematical modelling. Part 2 will appear in the November issue of Physics Education. Although this article will be read, in the main, by teachers of physics, we should perhaps remember that mathematical models are not confined to phenomena in physics and engineering. Indeed, mathematical models are extensively used in business, economics and politics (e.g. the treasury model), medicine and many other areas. Computers are often essential for solving the large system of equations which can result from all but the simplest models. The professional mathematical modeller has quite a task! He often has to determine whether a mathematical problem exists in the first place; if it does exist, then he must be able to state the problem in a suitable form. He is usually presented by a manager, or other responsible person, with a question such as: ‘The profits are down 10% on last year’s figures in our materials division. Can you help us discover the reason?’

Abstract: 'Notes on experiments' enables teachers at both sixth-form and tertiary level to share their ideas with other readers. Physics Education welcomes submissions from readers who know of some simple improvement to a commercially made piece of apparatus, or who have designed a new gadget or improved a standard experiment. In particular the Editor would welcome brief descriptions of experiments devised or procedures evolved during the course of project work or investigation undertaken by students; such submissions should be made under the joint name of the teacher and the student.

Abstract: The availability of data acquisition systems in the form of single integrated circuits provides an opportunity to apply microcomputers to a wide range of laboratory experiments with relative ease. The ADC0816, hereinafter called the 816, is one such system consisting of an 8 bit analogue-digital converter which has 16 input channels. Voltages of up to 5 V may be applied to each of the input channels and a particular input channel is selected by setting the corresponding 4 bit binary number on the address line of the multiplexer. The output from the system is an 8 bit binary number proportional to the voltage applied to the selected input channel. By altering the Typical result on a Pet screen

Abstract: = QR, by the first law. If we approximate to the changing force of the sun on the planet by replacing it by a sudden impulse at Q, the deviation of R into R‘ produced by this will be parallel to QO, by the second law. So AORQ = AOR‘Q = AOQP which is the law of areas. But what about all the terms introduced in these so called laws? Quoting Newton again: Dejnition 1: The quantity of matter is the measure of the same, arising from the density and bulk conjointly. Dejnition 2: The quantity of motion is the measure of the same, arising from the velocity and quantity of matter conjointly. Dejnition 4 : An impressed force is an action exerted upon a body in order to change its state of rest, or of uniform motion in a right line. He does not say how to measure an impressed force, but: Dejnition 8: The motive quantity of a (centripetal) force is the measure of the same, proportional to the motion it generates in a given time. So far as this goes we seem to be in the circular position of asserting that non-uniform motion is the sign of forces, that the forces are measured by the change of motion (i.e. rate of change of momentum, in modern parlance) and that the non-uniformity of motion results from the forces. Of course, the third law has not yet been invoked but if we are going to rely on it for the whole experimental contact, the other two laws being tautologies, this is putting an awful lot of weight on it-specially as it happens to be false for charges in motion! (For each moving charge is equivalent to a current element and the force between these involves a vector product and so is not ‘directed towards contrary parts’, i.e. along the line joining them.) Newton ’s laws of motion-rules or dlscoverles?

Abstract: For pt.I see Phys. Educ., vol.17, p.220 (1982). The authors present an example on mathematical modelling in the classroom, called 'Power from windmills', which has considerable potential for development both as a model and as a series of modelling exercises of increasing difficulty for students with different backgrounds.

Abstract: All too often students are turned off hard science because it seems to them to be the cult of the obvious. Scientific problems are not real problems because the answers are in the back of the book and, worse still, there is only one answer and that is the correct one! Opportunity for debate as well as the exercise of creative and imaginative thinking seem unnecessary. It is a pity that we do not make more use of the unexpected and unpredictable in physics education. Richard White (1979) has argued for the 'unusual experiment which engages the motions through being odd, dramatic, beautiful or puzzling', as one of a trilogy of experimental types (the other two being concerned with the experiments pertinent to daily life which enhance comprehension and true problem solving exercises to integrate student knowledge). If Professor Laithwaite's lectures and the amused disbelief on the faces of the audience are anything to go by, then the phenomena associated with circular motion qualify for the first type above! Our tireless fascination with gyroscopes, the wizardry in the art of billiards, not to mention the acrobatics of the Olympic diver, all demand as much from our imagination as they do from the conservation of angular momentum. And it needs only the geographer to remind us that while we spin on the rim of our planet at 1000 mph (-0.45 ms") the pseudoforces this generates drive the currents of wind and wave, make our weather and mystify their undergraduates! And it should not pass without comment that the chemist must blame these same forces for measurable effects in his vibration and rotation spectra. A simple experimental set-up which can persuade the heart as well as convince the mind with regard to what these forces can do is not easy to devise-although many have tried (Thompson 1973). The centrifugal force alone is relatively easy to comprehend and there is equipment on the market to provide what White would call 'generalised episodes' to aid understanding (e.g. Unsworth and Unsworth 1981). Gyroscopes are also not too difficult to come by. What we want to demonstrate, however, is the trajectory of an object on a rotating surface. Perhaps the simplest demonstration of this is to draw a straight line at constant velocity with a pencil out from the centre first of a stationary then of a rotating cardboard disc (figure 1). The curved path shows

Abstract: s ubmitted by T B Akrill, E Deeson, R W Fairbrother, W H Jarvis, P E Richmond and J Solomon.

Abstract: Most sane people agree that nuclear war must be avoided at all costs. Yet opinions are divided on the best means for achieving this end. According to recent opinion polls (see for example N A T O Reciew, October 1981) a majority favour a deterrence strategy for preventing nuclear war. But a growing number of people (if the recent increase in the Campaign for Nuclear Disarmament membership can be used as a gauge) believe that unilateral disarmament, and ultimately multilateral disarmament, is the only way of stopping a ‘nuclear holocaust’. The ‘nuclear debate’ was launched by Physics Education in September 1981. But this debate was entirely concerned with peaceful uses of nuclear energy. When will the ‘real debate’ begin-the debate about nuclear weapons? There has been a notable shortage of either information or discussion on the nuclear weapons issue in the publications of The Institute of Physics. The problem of nuclear waste may well concern our descendants, but it is the weapons debate which immediately concerns people. A school sixth-former was recently quoted in The Times Educational Supplement: ‘I can’t feel much conviction studying for my A-levels because I believe there will be a nuclear holocaust before I have grown up’. Partly as a response to such concern this article

Abstract: microprocessor which computes the toll charge from vehicle classifications entered on a keyboard, displays the charge to the vehicle driver and operator, and monitors the passage of the vehicle with the aid of detectors buried in the road surface. Recorded data are transmitted to the main computer in the central control room where information about traffic flows and cash receipts is continuously accessible on visual display screens. Toll charges can be varied by simple programming modifications and facilities are installed to introduce automatic vehicle identification and coin collection equipment if required. From the very outset of the project the consulting engineers advised the Humber Bridge Board that a project embracing such a huge structure would have a major visual impact on the environment and. throughout the period of design and construction, the engineers sought to achieve an aesthetic grace as well as satisfying engineering and economic requirements. I t is believed that the result is a visually stimulating entity.

Abstract: SEM will be used to check many of the production processes, ensuring that faults are spotted early and rectified, reducing costly wastage to a minimum. Life tested components can be analysed in the SEM to establish the cause of failure and therefore help in the design of new devices. A special application of the SEM involves operating an integrated circuit in the SEM chamber by means of electrical leadthroughs to an external power supply. The various potentials appearing on the circuit change the contrast seen on the image, and this technique can be used to locate faults beneath the surface of the device which cannot be detected by any other method. The SEM is continuing to find new applications in all branches of science, and instrumentation is constantly being developed to allow good quality results to be obtained quickly and simply.

Abstract: The author describes a very simple apparatus for measuring surface tension using the maximum bubble pressure method.

Abstract: to candidates in the pilot scheme. The drafts will be modified in the light of experience of their use. The Delegacy is confident that other institutions which have responded enthusiastically to the new examination will go on to develop courses in this area, either as part of initial training programmes or as in-service courses for serving teachers. The SATROS especially have expertise in educating teachers on industrial life. In terms of content this syllabus is a radical and exciting development in the field of public examinations. It is as remarkable for its mode of development as for its content. A syllabus geared to the study of manufacturing industry has emerged not because some determined individual or group of individuals has arbitrarily decided that it should, but because an extensive and open process of consultation led all involved to the conclusion that such an examination would fulfil a genuine need. Thus a process which began with representations from teachers concerning the narrowness of scope of certhin existing A-level syllabuses and the inappropriate nature of these examinations to the needs of many of their pupils is now coming to fruition. It is hoped that the period of evolutionary development will not cease with the completion of the pilot scheme and that industrial studies will have a wider importance than merely contributing to the process of preparing candidates for an annual public examination. We are confident that the encouragement and support received from teachers, industrialists and many organisations will ensure that this is so. The Delegacy would like to express its thanks to all those who have contributed to this work and in particular to the Industry-Education Unit of the Department of Industry for advice and expertise. Full details of the examination including syllabus, pattern of assessment, details of the case study, specimen examination papers and a resources list are available on request from The Secretary, University of Oxford Delegacy of Local Examinations, Ewert Place, Summertown, Oxford OX2 7BZ.

Abstract: For well over a decade there has been great interest in astronomy throughout all the age groups in our schools. Many people consider this to be due to the space age and its attendant ballyhoo from all branches of the communications media. I suspect however that the interest was there even before space became popular as a source of science spectaculars.

Abstract: neck and the ankle values both before and after exercise were calculated using the Student T-test. The results suggest that responses are generally slower after exercise but with no appreciable increase in delay between the foot and the head. Furthermore, responses appear more spasmodic from the foot after exercise ( p and standard eviation larger). Such results may be of interest to the footballer or car driver! It is interesting too to compare these results with a wider variety of reaction times, this time measured on a member of the technical staff (table 2). Notice how more careful rehearsal and performance of the experiment in this case reduces the standard deviation of the results. With regard to light and sound the Griffin reaction time apparatus was used but the switches were replaced by a more positive and quieter variety. Here the experimenter presses a two-way switch which both turns on a light or buzzer and starts the millisecond timer. The subject, on seeing the light or hearing the buzzer, presses a switch to stop the timer. The tendon jerk reflex reaction time was measured by

Abstract: Single-beam holographic techniques have been tried on double exposure holographic nterferometry (Jeong 1980, Hwu 1981, 1982a, b). This experiment applied the technique on time average holographic interferometry to study the mechanical vibrational resonance of a string vibrator at a very small amplitude. Qualitatively, taking time av rage holograms of a vibrator (vibrating in this manner) is like recording a double exposure hologram of the vibrator at its two maximum displacement positions, Figure 2 Signals interface connected between the J, and J, ports of the Pet on one side and the data, control and chip enable lines to the devices in use on the other. Connections key as figure 1. IC, is a 7405 octal inverter; IC, is a 7421 dual four-input AND gate; IC, is a 7409 quad two-input AND gate; IC, is a 6522 versatile interface adaptor (low enable pin 23 and high enable pin 24); resistors shown are all 1 kR

Abstract: The Humber Bridge, with a main span of 1410 m, has the longest bridge span in the world-l 12 nl more than the previous longest. Verrazano Narrows Bridge in New York. It is a suspension bridge, which is the only bridge form so far used for very long spans. A long-span bridge was necessary because the Humber estuary has a mobile bed and 1410 m covers the likely movements of the navigation channel; piers supporting short spans would have interfered with the natural regime of the river. The north tower is sited just above the high water line and the south tower is in the estuary about 500 m from the shore line. Because of topological and geological conditions there is a marked inequality in the lengths of the two side spans: that on the north side is 280 m long and that on the south side 830 m. However the bridge is so long that the asymmetry is not readily apparent. The bridge has been built to aid industrial and social development along both banks of the estuary. Distances between the major towns in the region, e.g. Grimsby, Immingham and Hull. have been cut by as much as 50 miles (80 km) and the bridge, together with its approach roads. forms a vital element of the integrated road system linking Humberside as a whole with the national motorway network. The structure carries dual two-lane roadways (which gives it a practicable capacity of about 40000 vehicles a day) with a combined footpath and cycle track along each side of the bridge. The underside of the road deck is a minimum 30 m above high water to give clearance for shipping using the river. Opened by the Queen in July 1981. the scheme is funded by tolls and is expected to reach its traffic capacity at about the end of the century. Design of the Humber Bridge and all the associated works was undertaken by Freeman Fox & Partners who had been retained as consulting engineers for the project since 1928, and had proposed designs in 1930, 1935, 1955 and 1966. When the project was finally authorised by the Government in 1971. the firm began detailed esign of the bridge and of the approach roads on both sides of the estuary. Under British practice the consulting engineers design the 'service' structure, i.e. the completed works that will safely do the job required-in this case, carry the traffic. They also prepare the specifications and tender documents, including the drawings, that describe and define what is required; and they advise the client, here the Humber Bridge Board, on the appointment of contractors. who have the responsibility for completing the project, with the consulting engineers supervising construction to ensure that the intended structure is built. The consulting engineers also adjudicate, on behalf of the client, on the fair price to be paid to the contractors for the work done. For the Humber Bridge, the Government has loaned the Bridge Board 75'; of the cost. the other 254, being raised in the money markets. The Board now operates the bridge and will repay the capital and interest out of toll revenues less operating costs. The bridge has been designed to carry the highway loading intensity specified in British Standard 5400 which deals with steel, concrete and composite bridges. The load intensity varies with the length of load considered with a minimum lane load of 8.7 kN m(approximately 600 Ib ftl); for short loaded lengths, the load intensity increases to 32.1 k N m (approximately 2200 Ib ftl) . In addition the bridge has been designed to carry a special vehicle with an all-up weight of 176 kN (180 tons). Consideration has been given to many patterns and combinations of loading, e.g. alternate spans being fully loaded with traffic on one side and empty on the other, so that the most onerous combinations of loading are catered for throughout the different elements-deck. suspenders, cables. towers. anchorages-of the bridge. Wind loading and its effects are of major importance for a bridge of this size of span and the design caters for wind speeds of approximately 47 m s l (105 mph) on the deck structure and, for the towers, a speed that increases with height to 66 m S ' (150 mph) at the top. Of even greater significance

Abstract: Part 1 of this article (Phys. Educ. 1981 16 352-6) described the AMSAT Oscar satellites, the NOAA weather satellites and the information they transmit. Part 2 deals with how to locate a satellite and the antennas and receivers required to receive information. There are two stages involved in finding the position of a satellite at a given time: (a) Calculation of the equatorial crossing time and position for the orbit required; (b) Extension of this data to the point where the satellite rises above the horizon of the listening station. As a satellite travels round the earth, its track makes an angle to the earth’s equator known as the satellite’s inclination, angle I on figure 1. The time at which the satellite crosses the equator when northbound (ascending node) is called the equatorial crossing time (ECT). The position of this crossing is usually given as degrees of longitude west of the Greenwich meridian. The orbital period of a satellite remains fairly constant, although over long periods a reduction in this time becomes apparent as the satellite height falls as a result of drag caused by the very thinly dispersed matter in its path. Each successive orbital track appears to move west by an amount referred to as the longitudinal increment, an effect produced largely by the rotation of the earth about its axis. Signals from the satellite can normally only be heard when the satellite is above the receiving station horizon and one can draw a circle on a map that

Abstract: It is the folklore amongst writers of elementary physics texts that gyroscopic precession is best introduced under the conditions where its motion appears most puzzling, i.e. steady precession under an external couple. It is widely believed that a vector diagram confined to one plane solves the problem and a superstition exists that the only possible outcome of a torque directed at right angles to the axis of spin is a precession about he mutually perpendicular direction-but despite appearances this is an impossibility. It may come as a surprise to learn that gyroscopic precession is possible without an external couple, and that an external couple can rotate the spin axis about the couple axis at the same angular acceleration as if the gyroscope were not spinning. Furthermore the precession of the total angular momentum vector and the precessional motion of the gyroscope are two quite distinct but dependent motions; accounting for the former does not successfully account for the latter. It is the purpose of this article to develop an intuitive understanding of this classical motion from basic principles while pointing out a few pitfalls in the common presentations. Satisfactory elementary accounts exist but may not be readily accessible, e.g. Worthington (1902), Crabtree (1909), Barker (1960), Feynman et al (1963). The majority of texts however offer unsatisfactory proofs, their true elements presumably distracting the reader from their false claims.