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5.1.2 Getting agreement with Gauss's law

Substituting the assumed form of the electric field (Equation 7.20) into the empty-space version of Gauss's law (Equation 7.16) gives

The first two partial derivatives are equal to zero because f does not depend on x or y. So we obtain


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The effects of mercury compounds on wildlife and on people

Mercury compounds have no effect on plants, but adverse effects have been demonstrated in a wide range of animals, including fish and amphibians (Boening, 2000). Very high levels of mercury have been found in the livers of American alligators in the severely polluted Everglades of Florida; these can be as much as 400 times greater than levels in alligators born and reared in alligator farms (Linder and Grillitsch, 2000).

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4.2 DDT: a classic case in ecotoxicology

DDT is very effective in controlling pests, being very toxic to insects, and is cheap to produce. Its effectiveness is enhanced because it is very persistent, remaining active in the environment for a long time. This increases its value as an insecticide to farmers because one application lasts a long time, but is also a major reason why it poses a threat to wildlife and to human health. Although the agricultural use of DDT was banned in most developed countries 30 years ago, it can still be
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Introduction

This unit examines why water shortages are predicted as a result of the world's growing population and the importance of access to clean and safe drinking water in public health. It looks at the distribution of water throughout the world and problems with contamination, topics of wide general interest.

Introducing health sciences: a case study approachI (SDK125)


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3.1 Graphs

Information is everywhere these days – in the form of images, written records, tables and graphs. In this part of the unit we want you to realise how useful graphs can be to analyse numerical information, and to show you some techniques that can help you decide how reliable this numerical information is.

It's often difficult to spot a trend or a relationship in a long list of numbers. Because the human mind is highly adapted to recognising visual patterns, it is often much easier to u
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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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2.2.2 Precision

Measuring the same sample should give the same result every time if the equipment is precise. In practice, the information displayed by a measuring device can depend on several factors (such as temperature and humidity) and can drift slightly over time. Nevertheless, during the time it takes to complete a measurement sequence, all measurements ought to remain within a specified, small margin of error, often marked on the equipment. We will see later on, in Author(s): The Open University

2.1 Differences between accuracy and precision

Accuracy is a measure of how close a result is to the true value. Precision is a measure of how repeatable the result is. For instance, a group of three friends tried the shooting gallery at a fair and their targets are shown in Figure 6. The first person was an expert marksman, but they were using a rifle with sights that had not
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1.6.1 Getting comfortable with factors of ten

Moving a decimal point by one place changes the value of the number by a factor of ten. For instance, to multiply a value by ten you can just move the decimal point one place to the right:

Notice that if the starting number doesn't have a decimal point shown we can place
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1.4.1 Study Note 2

An important point to remember when writing down measurements from a scale is never to quote more decimal places than you can reliably read from the measuring device you are using.

Figure 4
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3.12 Moon44: Apollo 17 station 1

The panorama was collected by Eugene Andrew Cernan at Station 1. Harrison H. "Jack" Schmitt is holding the rake. (QuickTime, 500KB, note: this may take some time to download depending on your connection speed)

3.9 Moon41: Apollo 15 station 2

The panorama was collected by James B. Irwin at Station 2. David Scott is to the left of the rover. He is examining a boulder. The large hill to the left of the rover is the summit of Mt. Hadley Delta. (QuickTime, 400KB, note: this may take some time to download depending on your connection speed)

3.2 Moon34: Apollo 11 station 3

This panorama was collected by Neil Armstrong from a spot north east of the landing module at the Sea of Tranquility. (QuickTime, 500KB, note: this may take some time to download depending on your connection speed)

6.3 Chemical formulas

By using symbols, elements can be represented much more conveniently and much more briefly. This method of using symbols can be extended to compounds. You will now look further into this idea using a very familiar compound: water. Recall which atoms there are in a water molecule.

Question 24

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3 What are compounds?

Activity 1: Elements and compounds

0 hours 10 minutes

Click on the video clip to watch Elements and Compounds, which focuses on water and its constituent elements.

Click below to v
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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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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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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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2.5 From phoneme to sentence structure: the syntactic problem

In the vervet monkey system, calls stand by themselves. Thus there is no syntax. Syntax can be thought of as working like road traffic rules do. It doesn't much matter which side of the road you drive on, as long as there is some clear convention. Similarly in (13), it is necessary to understand the difference between (13a) and (13b) without ambiguity, by having some rule or other about which noun phrase comes first. England may differ from most of the rest of the world in terms of the side o
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