POST-LISTENING

20. What do the words “pad” (03:06 – 03:12) and “fist” (06:06 – 06:11) mean?

21. How many parts can the video be divided into?

22. What headings can be given to each part?

OPTICAL FIBRES

Part I

1. What properties do optical fibres have?Where are optical fibres used?

Read the following text quickly and choose the best title A, B or C.

	A The history of cabling and telecommunications
	B A short introduction to optical fibres
	C Uses of glass in industry and technology
Optical fibres started to replace some uses of copper cables in the 1970s. They are made from glass and are usually about 120 micrometres in diameter. Some of the most common everyday uses are in telecommunications, close-curcuit television (CCTV), and cable television. 1. ___________________________________________ Optical fibres carry signals more efficiently than copper cable and with a much higher bandwidth. This means that fibres can carry more channels of information over longer distances. 2. ___________________________________________ Optical fibre cables are much lighter and thinner han copper cables with the same bandwidth. This means less space is needed in underground cabling ducts. 3. ____________________________________________ It is difficult to steal information from optical fibres. They are not harmed by electromagnetic interference, for example from radio signals or lighting. They don’t ignite so they can be used safely in flammable atmospheres, for example in petrochemical plants. 4. ____________________________________________ Optical fibres are more expensive per metre than copper. However, one optical fibre can carry many more signals than a single copper cable and the longer transmission distances mean that fewer expensive repeaters are required. Also, copper cable uses more electrical power to deliver the signals. 5. ____________________________________________ Optical fibres can’t be spliced as easily as copper cable. Employees need special training to handle the expensive splicing and measurement equipment.

* (the text is from: “Engineering” Workshop by Lindsey White, OUP; Unit 14, pg.16, ex.2)

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