Tap 318-4: Questions involving total internal reflection 

1.	Explain why substances with a high refractive index like diamond, sparkle. 

2. A pulse of white light is sent straight down a fibre optic cable 1 km long. The refractive index for blue light is 1.639 and for red light 1.621. What time interval will there be between the two components when they reach the far end? 

3. Calculate the critical angle of an optical fibre: 
a) without cladding if the glass has a refractive index of 1.56. 
b) when cladding is added of n = 1.49 
c) what advantage is this? 

The refractive index for light of wavelength 400 nm passing through a type of glass is 1.470; when light of wavelength 750 nm passes through the glass the measured refractive index is 1.455. 
4. To what colours do these wavelengths correspond? 

5. Which of these kinds of light travels faster in the glass? 

6. What is the ratio of the speeds of the two colours in air?