P1d(i) Light and Lasers You will learn about: Which factors affect the choice made to send a signal How laser light can be used

Early Messages Smoke signals were sent by the Ancient Greeks as did the American Indians. But their signals did not travel that far and they were weather dependent. Beacons can also be used to send signals but are also limited by weather conditions. Pigeons can also be used to send signals. These are faster so long as the pigeon makes the journey. Motorbikes are used today as they are faster and more convenient. Light travels much faster than any other message method. Ships today use light beacons to transmit Morse Code. Morse code was in operation by the Navy until LASER is an acronym for: L ight A mplification by S timulated E mission of R adiation. A laser produces a very intense narrow beam of light of a single colour – it is monochromatic. It can cut, burn or vaporise materials. Lasers can also be used for: transmitting communication signals, dental treatment, guiding missiles, light shown at public displays, and bar code readers.

Morse Code Morse code has been transmitted using mirrors and signalling lamps as well as by sound. The code is represented by a series of dots and dashes. This is a digital signal because the dots and dashes are a series of on and off signals. / / /.- - / This means: I can succeed at Physics!

Sending Signals Signals can be sent very quickly by light, radio or microwaves. ADVANTAGES: 1.They are almost instantaneous because all Electromagnetic waves travel at the same speed. 2.They can travel huge distances including through space. DISADVANTAGES: 1.Signals need to be coded otherwise anyone can intercept the message. 2.Most of these signals need to include wires or sophisticated electrical equipment which can easily be cut or sabotaged. The intended signal may not be sent. 3.The signal also needs to be amplified because the wave energy is easily lost over large distances.

Laser Light White light consists of different colours. Each colour is a different frequency and out of phase. Light from a laser is at one frequency so it is in phase. Laser light is monochromatic which means it is a single colour from one frequency and coherent which means the beam is in phase. The light form these waves is in phase because the peaks and troughs occur at the same time. The light form these waves is out of phase because the peaks and troughs occur at different times. Compact Discs, CDs, are pressed with a series of very tiny pits. There are billions of these pits and they each represent a digital signal. The signal is read using a laser. The music layer has a fine film of metal that coats it which follows the pits. This shiny film reflects the laser light. The metal layer is covered by a tough plastic layer to reduce any scratching. This means that the music code is sandwiched between the two layers. CDs

Questions 1.Why should you not look directly into a laser beam? 2.If you watch Star Wars the characters have laser lightsabers. How easy is it to see a laser? 3.Why are signals to Italy sent by microwaves? Why are telephones signals sent to your house form the local exchange by electric current?

Questions 1.Why should you not look directly into a laser beam? It may blind you or cut you. It is incredibly dangerous as it is a very intense narrow beam of light. REMEMBER: Never shine a laser into anyone’s eyes. 2.If you watch Star Wars the characters have laser lightsabers. How easy is it to see a laser? Very difficult because the beam is no narrow. 3.Why are signals to Italy sent by microwaves? Why are telephones signals sent to your house from the local exchange by electric current? The further a signal has to travel the more it needs to be amplified because energy from it is lost as waste, usually heat. So for long distances microwaves are best as they are fast and travel long distances. For local telephone signals wires are fine because the distances are much shorter. There is also less chance of the wires being cut or damaged.