Describe how a ray of light is able to travel along a curved optical fibre without escaping through the sides. State the name of the phenomenon and the condition required for the angle of incidence.

State one application of optical fibres in medicine and explain how they are used in this application.

Select the most appropriate speed from the list below for each of the following three waves:

1. Sound wave in air
2. Infrared radiation in a vacuum
3. Gamma rays in a vacuum

Possible Speeds:

• 340 m/s
• 1500 m/s
• 5000 m/s
• 3.0 × 10⁸ m/s
• 3.0 × 10¹⁰ m/s

The refractive index of diamond is 2.4. Use the speed of electromagnetic waves in a vacuum from (b) to calculate the speed of light in diamond.