1.7 Summary of Section 1 and questions Converging lenses or mirrors cause parallel beams of light to be brought to a focus at the focal point, situated at a distance of one focal length beyond the lens or one focal length in front of the mirror. Diverging lenses or mirrors cause parallel beams of light to diverge as if emanating from the focal point of the lens or mirror. Light paths are reversible, so a converging lens or mirror may also act as a collimator and
1.5.4 Image scale The nearest equivalent definition to angular magnification that is applicable to telescopes used for imaging onto a detector is the image scale (sometimes called the plate scale). Because of the importance of angular measures, the image scale quoted by astronomers indicates how a given angular measure on the sky corresponds to a given physical dimension in an image. The most common convention is to state how many arcseconds on the sky corresponds to 1 mm in the image. Fort
1.5.3 Angular magnification You may be familiar with the scales that appear on terrestrial maps or images obtained with microscopes, possibly stated as 1 : 100 000 or 1 mm corresponds to 1 μm. Scales such as these indicate how the size of the reproduction compares to the real thing. Image scales are no less important in astronomy, though they are usually stated in a different form, as we now explain. Imagine for a moment that you have the use of a telescope that allows you to observe Saturn and its ring system. It must
1.4.1 Deciduous trees During the winter months, a combination of factors, including lower temperatures, reduced light intensity and shorter days, means that plants can only photosynthesise at a slow rate and for restricted periods. As a result, photosynthesis cannot produce energy as fast as respiration expends it. In addition, water is often in short supply because of freezing, and so plants that do not have adaptations to conserve water, as conifers do, would lose water. Deciduous trees avoid these problems in w
1.2.1 The molecular level It is common knowledge that the freezing point of pure water is 0°C. Often, however, the temperature of water can fall below 0°C without it freezing, for two reasons: Any solvent containing a dissolved substance has a lower freezing point than when pure, which is why the sea freezes at a lower temperature than clean freshwater. The occurrence of supercooling, the phenomenon by which a fluid remains liquid at a temperature below
Introduction In this unit, we study one aspect of the fluctuating nature of an organism's environment. We consider how organisms living in a temperate climate, such as that in Britain, are adapted to cope with winter. You will see that there is much diversity of adaptations among organisms, with different species coping with the demands of a fluctuating environment in quite different ways. As cyclic variations are a widespread feature of environments, the range of adaptations to them is an important sourc
1.10 Summary and questions The Universe was created at the instant of the Big Bang. As it has aged, the Universe has cooled and distances within it have increased. At the earliest times, the four fundamental interactions were unified, but as the temperature of the Universe decreased, so these interactions became distinct. The earliest time about which anything can be said is the Planck time, when the gravitational interaction had a similar strength to the other fundamental interactions. Before this, the concept o
1.7 The hadron era Time: 10−5 s to 100 s Temperature: 3 × 1012 K to 109 K Energy: 1 GeV to 300 keV From the time that the temperature fell to about 3 × 1012 K, at about 10−5 s after the Big Bang, stable baryons (protons and neutrons) began to form from the up and down quarks that remained after the annihilation of matter and antimatter. 1.6 The quark-lepton era (contd) The next stage of the story is to look at how and when the original mixture of all types of quark and lepton that were present when the Universe was 10−11 s old, gave rise to the Universe today, which seems to be dominated by protons, neutrons and electrons. 1.1 A history of the Universe In the beginning there was nothing at all. To the north and south of nothingness lay regions of fire and frost. Snorri Sturleson, 1220 AD The cosmos is all there is, all there ever was, and all there ever will be. Carl Sagan, 1934–1996 The two viewpoints expressed above sum up the diffi Learning outcomes After studying this unit you be able to: discuss the sequence of the events that are believed to have taken place in the history of the Universe, particularly the particle reactions that occurred in the first few minutes after the Big Bang, and the role of unified theories in explaining those events; manipulate large and small numbers in scientific notation, and calculate values for quantities when given appropriate numerical information. 3.2 Number of progeny Female guppies begin to breed as soon as they become mature at about three months old; they then produce clutches of eggs, most of which become fertilized, at roughly one-month intervals until they die or become too old. Clutches vary in size from one to 40 eggs; the average clutch contains about 10 eggs. Thus, female guppies produce a large number of offspring during their lives, far more than can survive to maturity. 3.1 Introduction The purpose of this section is to consolidate your understanding of the theory of evolution through natural selection by looking at a specific example. The guppy (Poecilia reticulata) is a small fish whose natural habitat is small streams in northern Trinidad, but it is also a popular aquarium fish. Male and female guppies are very different in appearance (Author(s): 1 Charles Darwin Charles Darwin (1809–1882) briefly studied medicine in Edinburgh before going to Cambridge intending to become an Anglican clergyman. Soon after the voyage of the Beagle (1831–1836), during which he was gentleman companion to Captain FitzRoy, Darwin became convinced that biological evolution had occurred and saw how it could have been brought about by natural selection. Despite having gathered massive amounts of supporting evidence, Darwin refrained from publishing his revol 14 Final thoughts This unit started by asking simple questions such as ‘what science to teach?’ and ‘what is science?’ and pursued them to the point where answers proved both complex and elusive. Much of what I've said about such issues has been in the context of UK science education, though you'll be aware (e.g. see the Fensham reading) that m 3.1.1 (A) Science and certainty Pupils should appreciate why much scientific knowledge, particularly that taught in school science, is well established and beyond reasonable doubt, and why other scientific knowledge is more open to legitimate doubt. It should also be explained that current scientific knowledge is the best that we have but may be subject to change in the future, given new evidence or new interpretation of old evidence. 1 Unit overview In this unit we'll be concerned with what type of science forms the basis of science education, and for what purpose. You'll explore these issues by reading the text that follows and by tackling the activities that are included; there are also a number of readings. In the latter part of this unit (Sections 10–14) we'll consider some of the practical problems involved in delivering an effective curriculum in science and look at key questions relevant to all three educational tiers – Learning outcomes After studying this unit, you should be able to: demonstrate an understanding of problems associated with defining the Nature of Science; write in an informed way about the purposes of compulsory science education; be aware of the educational complications and implications associated with the phrase ‘the public understanding of science’; show an ability to comment critically on curriculum proposals that aim to promote science citi Parliament and the law Acknowledgements Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence
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How are rules made and who can influence this procedure? This unit will introduce you to the rule-making processes in of the UK Houses of Parliament in Westminster. You will examine how laws are enacted and how it is possible for unelected bodies and people to influence the content of such laws. First published on Wed, 15 Jun 2011 as Author(s):
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