'A' Level Medical Option Questions - The Endoscope


(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.

Laser light is monochromatic. It is composed of waves of single frequency/wavelength, whereas the light from a lamp consists of a range of wavelengths.

Laser light is collimated. An approximately parallel beam is produced. A lamp produces light that spreads out in all directions from the source.

Laser light is coherent - waves produced are in constant phase with each other; whereas light from a filament lamp is incoherent.

Two correct properties one mark each each

Correct explanation one mark for each

(3 marks Maximum)

(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,

To illuminate the inside of a body - such incoherent light can be sent down the light guide.

(ii) a use of the light from a laser.

Cauterising - stopping bleeding/cutting tissue/treatment of tumours

(2 marks)

(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.

(2 marks)

Ray reflects at core/cladding boundary.

Ray refracts as it leaves the fibre - bending away from the normal.

(ii) Complete the graph below to show how the refractive index changes with radial distance along the line ABCD in the figure above.

n (constant) = 1.5 from A to B,

slight decrease and constant from B to C

at C, n decreases to 1, remains at 1 from C to D

(ii) Calculate the value of the angle of incidence, i, shown in the figure above.

1.5 = sin i/sin 10

i = 15º

(4 marks)

(Total 11 marks)