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Unit 2 Physics 2011 Wave –like Properties of Light Data Analysis Name: Mark: /25 45 minutes, Scientific Calculator and A4 sheet of notes allowed. Fibre optic cables work by shining a light beam through a glass fibre. The beam needs to be Totally Internally Reflected on the inside surface of the fibre as shown. ____________________________________________________________________________________________ Q1 A laser beam enters an optical fibre as shown below. Use the information on the diagram below to calculate the angle of refraction. (2 marks) RIair = 1.00 RIglass = 1.50 53° ______________________________________________________________________________________________ Commercial fibres are usually constructed as a transparent core surrounded by a second transparent skin, called the cladding, as shown. Q2 A manufacturer has two types of glass available as shown in the table below. He would like to use one type as the core and the other as the cladding. Type Glass A Glass B Refractive Index 1.52 1.43 Which glass should he use as the core? Explain your answer. (3 marks) Q3 Calculate the critical angle at the core – cladding interface. (2 marks) Cladding Core Cladding Q4 On the diagram above, draw a beam at the critical angle, which you calculated in Q3. Label the angle. (2 marks) Q5 Draw a second beam at a different angle that will also be totally internally reflected. (1 mark) Q6 The light beam now encounters a tight bend in the fibre as shown. Draw an annotated diagram to show what happens to the beam at the core – cladding interface. (2 marks) Q7 The manufacturer thinks that it would be cheaper to contain the light to the core by replacing the cladding with a black plastic coating. Is this a good idea? Explain your answer. (2marks) _____________________________________________________________________________________________ On a closer inspection the manufacturer notices that there are two refractive indices given for Glass A. At a wavelength of 670nm At a wavelength of 450nm RI = 1.50 RI = 1.54 Q8 Use the attached Electromagnetic spectrum to determine as closely as possible the nature of each of the two wavelengths. (2 marks) Q9 Calculate the speed of the 670nm wavelength EM radiation in Glass A. (2 marks) Q10 Is the 450nm radiation be slower or faster than the 670nm radiation in the glass? (1mark) Q11 A very short pulse of white light is sent through a long fibre made of Glass A. Describe how the pulse appears at the other end. (2 marks) Q12 The manufacturer has a choice of two light sources to use with his fibre optic cable. A bright light bulb giving pure white light A red laser Which should he use? Explain your answer. (2 marks) Q13 Two fibre optic cables have been set up to shine a red and a green light onto a white screen. What colour would you see if the two lights both over-lapped as shown? (2marks) Red Green ________________________________________________The End________________________________________