IELTS Preparation Series 2, Episode 6: Lasers
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Hello. I'm
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Margot Politis. Welcome to Study English, IELTS preparation.
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Today we're going to learn about lasers - what are they, and how they work.
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We'll also practice structuring a description of how something works, and we'll work on
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our vocabulary for describing colours.
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Let's begin by listening to Imogen Jubb talk about the history and the science of lasers.
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Lasers are used in all sorts of settings like welding,
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cutting,
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surgery,
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communications,
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reading bar codes at the supermarket
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or reading the information stored on a CD or DVD.
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There are many types of lasers but they all have 3 main parts to them. They all have an
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energy source, such as a lamp, some sort of feedback mechanism, like this pair of mirrors,
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and also some medium, like the ruby crystal, which can amplify the light.
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Now the first laser was built in the 1960s. It was made from a ruby crystal, some lamps
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and 2 mirrors, one on either side of the crystal.
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I've got a sort of model of it here.
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The lamp shines white light onto the crystal, which is represented by this tube. Pumping
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energy into the crystal actually gives off light at a particular frequency to produce
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a particular colour.
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Some of this light bounces backwards and forwards between the two mirrors, and passes through
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the crystal each time.
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Each time the light goes through the crystal, it gets amplified, stimulating the same energy
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release in other parts of the crystal. So after many times in between the two mirrors,
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and many reflections passing through the crystal, you end up with a very strong, narrow beam
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of light that is just one colour.
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One of the mirrors is only partially reflective, so some light passes out as the laser beam.
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Before Imogen explains the laser to us, she starts with an 'introduction', or 'orientation'.
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That way, we know what to focus on.
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If you're describing a device or a tool, it's a good idea to introduce it by naming it and
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describing what it's used for.
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This is useful in spoken English, and it's also a good way to begin if you are writing
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in formal English.
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Listen to how Imogen introduces the laser.
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Lasers are used in all sorts of settings like welding,
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cutting,
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surgery,
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communications,
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reading bar codes at the supermarket
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or reading the information stored on a CD or DVD.
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She talks about the function of the laser and lists a few of the things we use lasers
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for today.
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In formal writing, if you were to introduce a discussion of lasers, you could structure
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your opening paragraph in a few ways.
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One idea would be to start like this:
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A laser is a device designed to intensify a beam of light.
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Or, you might choose to write:
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The diagram is of a laser designed to scan barcodes.
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But Imogen chooses to begin by telling us what lasers are used for.
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She begins:
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Lasers are used in all sorts of settings.
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In your introduction, you could give some background about the device.
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Once the device has been introduced, you can talk about it in more detail.
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Let's listen to Imogen describe the parts of the laser. How many parts are there and
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what are they?
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There are many types of lasers but they all have 3 main parts to them. They all have an
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energy source, such as a lamp, some sort of feedback mechanism, like this pair of mirrors,
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and also some medium, like the ruby crystal, which can amplify the light.
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She talks about three main parts.
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All lasers have: an energy source, a feedback mechanism, and a medium to amplify light.
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In formal writing, we could structure this information in a number of ways.
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We might say that:
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A laser consists of a number of parts.
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Or:
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All lasers are comprised of three parts.
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Both of these sentences are structured to include a subject,
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a verb, and an object.
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You would then follow with a list or another sentence detailing exactly what the three
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parts are, in order:
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These are the energy source, the feedback mechanism and, finally, a medium to amplify
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the light.
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Imogen then explains how each part of the device functions. Let's listen as she describes
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each part.
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The lamp shines white light onto the crystal, which is represented by this tube. Pumping
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energy into the crystal actually gives off light at a particular frequency to produce
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a particular colour.
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Some of this light bounces backwards and forwards between the two mirrors, and passes through
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the crystal each time.
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Each time the light goes through the crystal, it gets amplified, stimulating the same energy
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release in other parts of the crystal.
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So you can see how Imogen has built up a clear image of the device.
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In formal written English, you might finish off by explaining the 'purpose' of the device.
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You could say:
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The purpose of the laser is to generate an intense beam of light.
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Let's hear how Imogen finishes her description.
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So after many times in between the two mirrors, and many reflections passing through the crystal,
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you end up with a very strong, narrow beam of light that is just one colour.
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She finishes by talking about what the purpose of the laser is, what it produces.
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She says:
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You end up with a very strong, narrow beam of light.
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So let's review how Imogen has structured her explanation.
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First, there was an 'introduction' to the object. Imogen told us that we were talking
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about the laser and then gave us some background.
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She then moved into the 'body of the description'. She told us that it is made up of three parts,
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and listed those parts.
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In your writing, you might write three separate 'body paragraphs' - one for each of the parts.
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Then, you'd finish off with a 'statement of purpose' - what the object's overall purpose
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is.
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Now let's finish by listening to Imogen one more time, and then we're going to talk about
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colours.
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The lamp shines white light onto the crystal, which is represented by this tube. Pumping
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energy into the crystal actually gives off light at a particular frequency to produce
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a particular colour.
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When energy passes through the crystal, it gives off a particular colour of light. Light
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contains all the colours of the 'spectrum', or the 'rainbow'.
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These are:
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red orange
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yellow green
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blue indigo
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violet
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We talk about shades of colour in different ways - most commonly by using light and dark.
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For example:
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light blue dark blue
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Or sometimes we refer to nature, for example:
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sky blue
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forest green
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fiery red
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We also use precious stones to describe colour. For example:
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sapphire blue
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emerald green
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ruby red
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And that brings us to the end of Study English today.
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But for more information on structuring descriptions go to our website. You will find notes, exercises
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and quizzes to help you.
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Just go to abcasiapacific.com/studyenglish.
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And I'll se you next time for more IETLS preparation. Bye bye.
