TE Enriched Sample (E)

Endoscopy Exercise 83 2.3 1. The core and the cladding of an optical fibre have refractive indices of 1.55 and 1.45, respectively. What is the critical angle at the core–cladding boundary? A. . . sin 1 45 1 1 55 1 1 - - c m B. . . cos 1 45 1 1 55 1 1 - - c m C. . . sin 1 55 1 45 1 - c m D. . . cos 1 55 1 45 1 - c m 2. A light ray leaks from the core to the cladding in an optical fibre. The angle of incidence and the angle of refraction are 15° and 20°, respectively. Which of the following is the closest to the value of the critical angle on the core–cladding boundary? A. 45° B. 50° C. 60° D. 70° 3. A coherent fibre bundle of diameter 6 mm contains 10 000 fibres. What is the approximate average distance between the centres of two adjacent fibres? A. 0.02 mm B. 0.03 mm C. 0.04 mm D. 0.05 mm 4. Which of the following parts is not suitable to be inspected by endoscopy? A. eye B. lung C. ovary D. stomach 5. The core and the cladding of an optical fibre have refractive indices of 1.485 and 1.455, respectively. cladding i c cladding core (a) Find the critical angle c at the core–cladding boundary. (b) What is the maximum entrance angle i so that light enters the core from the air and can be guided through the fibre? 6. There are two kinds of fibre bundles in an endoscope. (a) What are the differences between them? Briefly explain. (b) Which one is used for transmitting images? What is the typical function of another bundle? C B D A 78.5° 17.3° 7. An instrument is inserted into a patient’s colon for medical examination. Shown below is a series of photos taken from the outside of the patient’s body. (a) Suggest a possible instrument. (b) When using the above instrument, there are some limitations and precautions. (i) What limits the resolution of the images? (ii) Suggest one preparation when taking the above photos. (iii) Suggest one possible risk when taking the above photos. 8. A finer fibre can bend more than a thick one while light can still be guided through. Go through this question and see why this is so. Suppose a fibre has a diameter of D . Its core and cladding have refractive indices of 1.48 and 1.45, respectively. (a) What is the critical angle at the core–cladding boundary? (b) The fibre is now bent with a bending radius R . A light ray originally parallel to the fibre strikes the inner curved surface of the core with an angle of incidence i . core cladding D i R (i) Express i in terms of R and D . (ii) What is the condition that i has to satisfy such that the light ray is totally reflected by the internal side of the core? (iii) Hence, briefly explain why a finer fibre can bend more, given that the light can still be totally reflected by the internal side of the core. (c) Apart from bending, give one more advantage of using finer fibres in a coherent fibre bundle. Endoscope 78.4° sin i R D R 1 = + - R > 48.3 D Higher resolution (2.3) Sample © United Prime Educational Publishing (HK) Limited, Pearson Education Asia Limited 2023 All rights reserved; no part of this publication may be reproduced, photocopied, recorded or otherwise, without the prior written permission of the Publishers.