What is a flexible endoscope?

A flexible endoscope is an instrument built around bundles of optical fibres that allows the inside of a body cavity or a piece of machinery to be lit up and viewed from outside.

Why must the image-carrying bundle of an endoscope be coherent?

Each fibre carries the light from one small part of the object, so unless the fibres keep the same relative positions at both ends the parts of the picture arrive in the wrong places and the image is scrambled.

Why does the illuminating bundle of an endoscope not need to be coherent?

It only has to deliver light to the far end, and it does not matter which particular fibre any part of that light travels along because no image is being carried.

What is the purpose of the objective lens at the tip of an endoscope?

The objective lens forms a small real image of the object on the end face of the coherent bundle so that the fibres can pick it up.

CCEA A-Level Physics 1210

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Refraction

The flexible endoscope

3 things to know
Unit AS 2

Overview

Flexible endoscope, coherent fibre bundle and how an endoscope is used in keyhole surgery.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Name the two fibre bundles in an endoscope and state what each does.

Key term

What is a coherent fibre bundle?

Key term

What is at the viewing end of the coherent bundle of an endoscope?

Questions from this subtopic

Each one with the model answer underneath.

1
What is a flexible endoscope?
Model answer
A flexible endoscope is an instrument built around bundles of optical fibres that allows the inside of a body cavity or a piece of machinery to be lit up and viewed from outside.
2
Name the two fibre bundles in an endoscope and state what each does.
Model answer
The illuminating bundle carries light from a bright external source down to the far end, and the coherent bundle carries the image of the illuminated object back to the observer.
3
What is a coherent fibre bundle?
Model answer
A coherent bundle is one in which every fibre occupies exactly the same relative position at both ends, so the pattern of light picked up at one end is reproduced in the same arrangement at the other.
4
Why must the image-carrying bundle of an endoscope be coherent?
Model answer
Each fibre carries the light from one small part of the object, so unless the fibres keep the same relative positions at both ends the parts of the picture arrive in the wrong places and the image is scrambled.
5
Why does the illuminating bundle of an endoscope not need to be coherent?
Model answer
It only has to deliver light to the far end, and it does not matter which particular fibre any part of that light travels along because no image is being carried.
6
What is the purpose of the objective lens at the tip of an endoscope?
Model answer
The objective lens forms a small real image of the object on the end face of the coherent bundle so that the fibres can pick it up.

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