The body has many twists and turns. However, we know that light travels in straight lines. For this reason, the light in an endoscope is made to ‘bend’ through the optical fibres.
20.2 Light ray
1. When light passes through optical fibre, it begins to refract. This is because the outside of the fibre is less dense than the middle.
Total internal reflection
2. If the light strikes the boundary of the layers in an optical fibre at a large angle, it does not refract but reflects instead.
3. This light then bounces along the inside of the fibre. This is called total internal reflection.
Bending light
The following set-up demonstrates how an optical fibre ‘bends’ light:
Medical Bottle of water
technology: good or bad?
Fig. 20.2.9 Total internal reflection in an optical fibre
Pin hole Laser
Stream of water
Fig. 20.2.10
1. Predict what will happen when the laser is turned on and shone through the bottle.
2. Using your knowledge of total internal reflection, explain why you have made this prediction.
3. Your teacher can demonstrate this investigation in the school laboratory. Record your observations.
4. Explain why your predictions did or did not match your observations.
Safety note: never look directly into the beam of light emitted from a laser as it could seriously damage your sight.
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While it is clear that medical technology has led to us living longer, there may be some negatives. In groups of four, prepare a debate about the statement ‘Medical technology: good or bad?’
Fig. 20.2.9 Total internal reflection in an optical fibre
