'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.

In a coherent bundle fibres are maintained in fixed positions relative to each other whereas in a non-coherent bundle fibres have no fixed relative positions. This means that a coherent bundle can be used to tranmit images mage up of light energy whereas non-coherent ones just transfer the light energy and image transfer is not possible.

(2 marks)

(b) State an application for each type of bundle.

Coherent bundles of fibres can be used to transmit images of internal organs of the body so a doctor can 'see' inside a patient.

Non-coherent bundles can be used to transmit (or conduct) light to the inside of the human body. This illuminates the site that the doctor wishes to view.

(2 marks)


(i) Give two advantages of a bundle consisting of fibres of very small diameter over a bundle consisting of larger fibres.

High resolution (fine detail) images can be seen if the fibres are of small diameter. The bundle would also be more flexible than if thicker fibres were used. The fine fibres would also allow bending around tighter curves without light escaping. (MAX 2)

(ii) Give two reasons why a glass cladding is used around the central core of each fibre in a coherent bundle.

Scratches on the outer surface would allow light to escape - the cladding protects the outer surface.

Close contact between adjacent fibres (or liquid penetrating between fibres) would allow light to pass from one fibre to another, the cladding ensures that image is not confused (corrupted, scrambled) - it prevents light passing between individual fibres.

(4 marks)

(Total 8 marks)