Download Unit 2 Wave-like Properties of Light

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.
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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°
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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)
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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
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