P1D

- Using light increases the speed of communication.

- Total internal reflection is when a wave stays inside a material by bouncing off the internal walls.

- Total internal reflection occurs when the angle of incidence is equal to or bigger than the critical angle for materials.

- If the angle of incidence is too small the light will leave the material rather than staying inside.

- Lasers produc an intense, narrow beam of light of a single colour.

- The waves in a laser beam are coherent, which means they are all in phase.

- Lasers can be used in surgery, dental treatment and weapon guidance. 

- Morse code is a series of on and off signals, which means it is digital

Advantages:

- Signals travel fast.

- Multiplexing means that lots of different signals can be transmitted down a single optical fibre at the same time.

- Little interference. 

- The surface of a CD has a pattern of billions of shallow pits cut into it. The areas between the pits are called lands. 

- A laser shone onto the CD is reflected from the shiny bottom surface as it spins around in the player.

- The beam is reflected from a land and a pit slightly differently - and this difference can be picked up by a light sensnor. 

The ray of light enters the fibre so that it hits the boundary between the core and the outer cladding at an angle greater than the critical angle for the material. This causes total internal reflection of the ray within the core.