Light and lasers (P1d)

Light and lasers (P1d)

1. Morse code

   • The Morse code uses a series of dots and dashes to represent letters of the alphabet
     • This code is used by signalling lamps as a series of short and long flashes of light
     • It is an example of a digital signal

2. Sending signals

   • When a signal is sent by light, electricity, microwaves or radio, it's almost instantaneous
   • Each method of transmission has advantages and disadvantages
     • Can the signal be seen by others?
     • Can wires be cut?
     • How far does the signal have to travel

3. Laser light

   • White light is made up of different colours of different frequencies out of phase
   • Laser light has only a single frequency, is in phase and show low divergence.
   • Laser light is used to read from the surface of a compact disc (CD)
     • The surface of a CD is pitted
     • The pits represent the digital signal
     • Laser light is shone onto a CD surface and the difference in the reflection provides the information for the digital signal

4. Critical angle

   • When the light travels from one material to another, it is normally refracted
   • If it is passing from a more dense material into a less dense, the angle of refraction is larger than the angle of incidence.
   • When the angle of refraction is 90%, the angle of incidence is called the critical angle
   • If the angle of incidence is bigger than the critical angle, the light is reflected:
     • This is total internal reflection
   • Some fibres are coated to improve reflection
   • Telephone conversations and computer data are transmitted long distances along optical fibres at the speed of light (200000 km/s in glass)

5. Endoscopy

   • An endoscope allows doctors to see inside the body without the need for surgery
     • Light passes along one set of fibres to illuminate the inside of the body
     • The reflected light passes up another set fibres to an eyepiece or camera
     • The light is reflected

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