'A' Level Medical Option Questions - The Endoscope

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.

In the coherent bundle the fibres retain the same relative position to each other at both ends of the cable. The coherent cable transfers images from inside of body to the viewer.

In the non-coherent bundle of fibres there is no relative order to the fibres. The non-coherent bundle simply works as a light guide. It carries light into body/for illumination purposes.

(4 marks)

(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

sin c = n2/n1 = 1.55/1.60

c = sin-1 (1.55/1.60) = 75.6o

(1 mark)

(Total 5 marks)