5.1 Electromagnetic waves

This section gives a brief introduction to light and electromagnetic waves.

The idea that light is an electromagnetic wave had occurred to Faraday while Maxwell was still a schoolboy, but Maxwell was the first person to possess a complete set of equations describing the dynamical behaviour of electric and magnetic fields. Believing that Faraday was correct, Maxwell set out to show that his equations have wave-like solutions that propagate through empty space at the speed of light.


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6 Self-assessment questions

Question 1

Give three reasons why many people in the world face an increasingly severe shortage of fresh, safe water.

Answer

The human population of the world i
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2.5 What is a sensible dose?

This will vary from drug to drug and patient to patient, but bear in mind that most drugs need to be swallowed or injected, so the manufacturer has designed the dose sizes to be as easy as possible for a patient to take and for the health worker to administer.

The following dose ranges are the most sensible and practical for adults:

Table 7 Typical drug doses

<
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2.6.2 (b) Using spheres

Chemists have their own convention for representing molecules and their constituent atoms. As in Figure 6, they often use circles (or spheres if they make a three-dimensional model) to represent atoms – and they often use short, straight lines between the circles to represent the bonds that join one atom to an
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2.6.1 (a) Using Lego as a model

In this kind of building set, there are a limited number of types of block and each block has a particular shape. Just as importantly, each one has a particular way in which it can link to other blocks because of the way the studs are arranged.

The blocks can help you see how the atoms link in a molecule of water. Look at Figure 7 where the red brick represents an oxygen atom and the white bricks represent hydrogen atoms. There are only two locations where the hydrogen atoms can join th
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2.5 What is water made of?

The size of a water droplet may seem very small but in terms of the scale of scientific measurement it is relatively large. You already know that water is made up of molecules so now consider a water droplet more closely to see what water molecules are made up of. If you could magnify a water droplet until it no longer has a smooth surface, you would see something similar to that shown in Author(s): The Open University

2.4 Going down: using scientific notation for small numbers

You saw in Section 2.2 how the powers of ten notation provides a concise method of expressing very large numbers and reduces the chances of errors when, otherwise, many zeros would have to be written out. You will now see how the powers of ten notation can be extended to cover small numbers, such as 0.000 000 0002 m.

Write down th
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2.3 The study of a raindrop

Most of the usable water is derived from the 1.1 × 105 km3 that falls over the land surface each year as rain, snow, sleet or hail. The collective term for all of these sources of water is precipitation. At this point, you will consider the size of the drops of water that make up clouds or rain (Figure 5).

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2.1 Where water occurs and how we measure it

When astronauts first ventured to the Moon in the late 1960s, they were captivated by a vision of the Earth in colour as it had never been seen before (Figure 2). It is not surprising that, after pictures like this were published, the Earth became known as the ‘blue planet’.

Figure 2
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Learning outcomes

By the end of this unit you should be able to:

  • read data presented in tables;

  • use scientific notation to express both large and small quantities;

  • appreciate why chemists use different models to represent molecules;

  • identify the number and type(s) of atom present in a molecule from its chemical formula;

  • identify the reactants and products of a reaction in a chemical equation;

  • read and write using chemical
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Introduction

This unit is an introduction to chemistry concepts, using water as the main illustration. Much of the unit is devoted to exploring the smallest water particle – a water molecule – what it is and how it gives rise to the particular properties of water. The unit also explains powers of ten and scientific notation, which are a convenient way of expressing both very large and very small numbers. It is a good introduction to science.

This unit is an adapted extract from the course
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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions). This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

The content acknowledged be
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4 Conclusions

Activity 3

Read back over Section 3. Make two columns on a piece of pap
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3.4 Specialisation within language areas: brain scanning

Is there any evidence from the undamaged brain that the view derived from aphasia is indeed correct? The most useful methodologies here use either PET or functional MRI (fMRI) scanning to establish which parts of the brain are active in particular tasks. The difficulty is that a standard linguistic task, such as understanding a sentence's meaning, involves phonology and syntax and semantics, and thus is not helpful when trying to tease out which of these subtasks happens in which areas.


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3.3 Specialisation within language areas: aphasia

Aphasia is caused by localised brain damage, for example due to a stroke or an automobile accident. General intellectual functioning is not necessarily impaired, as the person can still perform non-linguistic tasks. Nor is the understanding and production of language necessarily completely abolished. Instead, there are highly specific patterns of impairment in the way language is processed.

Aphasia is divided into two main types, fluent and non-fluent. For reasons which will become appa
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2.6 Summary of Section 2

Human language is a complex communication system that allows the generation of infinitely many different messages by combining the basic sounds (phonemes) into words, and combining the words into larger units called sentences. The way the sounds combine is governed by phonological rules, and the way the words combine is governed by syntactic rules.

Phonemes can be divided into the vowels, which are made by vibration of the vocal folds, and consonants, which are abrupt sounds made by bri
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2.4 From phoneme to meaning: the semantic problem

For a vervet monkey, once an alarm call has been assigned to the correct phonological class – leopard, snake or eagle – then the task is straightforward indeed. Each of these sound patterns is connected in long-term memory to some ‘prototype’ of the predator in question, including what it looks like, what it does and so on. The eagle call always means eagle, whatever the context. The activation of the brain trace for the eagle call invariably activates the
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2.3 From ear to phoneme: the phonological problem

The phonological problem is the problem of knowing which units (words, calls) are being uttered. The speech signal is a pattern of sound, and sound consists of patterns of minute vibrations in the air. Sounds vary in their frequency distribution. The sound of a flute playing is relatively harmonic. This means that the energy of the sound is concentrated at certain frequencies of vibration. A plot of the energy of a sound against the frequency at which that energy occurs is called a spe
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2.2 Generativity and duality of patterning

Let us now reconsider the sentence you heard in the imaginary scenario at the beginning of this unit. Here it is again.

  • (1)  My dad's tutor's no joker, and he told me the TMA's going to hit home with a bang.

Activity 2

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7.3 The descending auditory pathway

The auditory system transmits information from the cochlea to the auditory cortex. Another system follows a similar path, but in reverse, from the cortex to the cochlear nuclei. This is the descending auditory pathway. In general, the descending pathway may be regarded as exercising an inhibitory function by means of a sort of negative feedback. It may also determine which ascending impulses are to be blocked and which are allowed to pass to other centres in the brain. The olivocochlear bundl
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