Total internal reflection

Question 1

Describe the conditions for total internal reflection to occur for a ray of light.

Answer 1

Light needs to travel from a denser material to a less dejae material, and the angle of incidence needs to be above the critical angle.

Question 2

What is an endoscope and how does it work?

Answer 2

Endoscopes can be used to look inside patients’ bodies and make use of optical fibres. Endoscopes allow ‘keyhole’ surgery. This is surgery conducted through a very small cut in the body to speed up recovery time.
Light is sent into the optical fibre above the critical angle and is totally internally reflected along the fibre to the object being viewed, where it is then reflected back up to the observer.

Question 3

Explain the role played by reflection and refraction in an endoscope.

Answer 3

Light rays are reflected at the interface between the fibre and the outer sheath so that the light rays travel down into the patient and are then reflected back. The angle at which the light waves meet this boundary must be greater than the critical angle for total internal reflection to occur, and the outer sheath must be less dense than the fibre.