'A' Level Medical Option Questions - The Endoscope
Bundles of optical fibres are described as either coherent or non-coherent.
(a) Describe how the fibres are arranged in each type of bundle and explain how the different designs determine their optical characteristics.
(b) State an application for each type of bundle.
(i) Give two advantages of a bundle consisting of fibres of very small diameter over a bundle consisting of larger fibres.
(ii) Give two reasons why a glass cladding is used around the central core of each fibre in a coherent bundle.
(Total 8 marks)
Q2. The diagram shows a glass optical fibre with a central core of refractive index 1.55 and a surrounding cladding of refractive index 1.40.
(a) Calculate the critical angle, C, for the boundary between these two types of glass.
(b) Complete the path of the light ray shown in the diagram.
(c) State and explain whether the following changes in the optical fibre would increase or decrease the probability of light escaping from the fibre.
(i) increasing the refractive index of the cladding
(ii) bending the fibre into a tighter curve
(Total 8 marks)
(a) State and explain two physical properties of the light produced by a laser which makes it different from the light produced by a filament lamp.
(b) An endoscope may use light from a filament lamp and light from a laser. State
(i) the use of the light from a filament lamp,
(ii) a use of the light from a laser.
(c) The figure below shows a cross-section through an optical fibre used in an endoscope. The core is made from glass of refractive index 1.5.
(i) Complete the path of the ray through the fibre and out at the other end.
(ii) Complete the graph below to show how the refractive index changes with radial distance along the line ABCD in the figure above.
(ii) Calculate the value of the angle of incidence, i, shown in the figure above.
(Total 11 marks)
Q4. An endoscope contains two bundles of optical fibres.
(a) Name the two bundles. For each bundle state clearly the arrangement of the fibres and explain its purpose in the operation of the endoscope.
(b) Each fibre has a core surrounded by cladding. Calculate the critical angle at the core – cladding interface of a fibre.
refractive index of core = 1.60
refractive index of cladding = 1.55
(Total 5 marks)
(a) The diagram shows the cross-section through a clad optical fibre which has a core of refractive index 1.50.
Complete the graph below to show how the refractive index changes with the radial distance along the line ABCD in the diagram above.
(b) In the optical system of a flexible endoscope there are two types of fibre bundles, coherent and non-coherent. Explain the purpose of each of these two types of bundle.