Telephone
What makes the invention important?
The ability to communicate instantly between two places. The phone revolutionized communication between two places. Before phones communication was done by mail and telegram and was very slow.
How telephone works?
Telephone has two main parts, the receiver and transmitter. When a person speaks in the telephone, he speaks to the transmitter, his voice is picked up by the microphone which transforms the soundwaves of the person in to the copperline so that the sound can be carried out to the other person. In order for the sound waves to move in the line, a small electric current is needed. So basically, the sound waves are transformed into electric current which takes the information from point A to point B. When the electric current have reached the receivers end of the line, the speaker transforms that electric current back into sound so the voice can be heard. The current in the the telephone line varies. The reason why is that the different kinds of voices need different amount of current to pass through thus creating the sound in the receiving end.
At first, when calling to someone, the call went first to a call center where the operator was told to whom the call was was supposed to go. And then the operator connected the lines and the call went through. Then came the phones with rotary dial. In the rotary dial, the numbers are combined into circular layout. In this dial, every number generates electronic pulses. When the pulses reached the call center, they were automatically connected to the receiving caller. After that came the touch tone dialing, in which each touch created unique tone, and when pressing more than one button at the same time, the tones are mixed. In this kind of phone dials, after the desired number is pressed, the tones are carried to a telephone center, where the tone memory/connector picks up the right number to connect the call.
At first the needed electric current was made by cranking up the magneto which would generate the current or by using a battery. Nowadays the current comes from the power grid and in mobile phones the phone battery.
About the wire
The wires are insulated. There are two twisted wires, audio and control signal. The twisted pair line rejects electromagnetic interference. There are amplifiers for the signal. There is also a junction box that adjusts the line’s resistance. This results in better signal power.
About the microphone:
One of the most popular ways to record sound is RF condenser microphone (RF = radio frequency). It is used in telephones and high-fidelity recording microphones. RF condenser microphone can produce very good sound quality. It doesn’t need a big mass to be moved by the soundwave. This means that RF condenser microphone needs a separate power source.
How does sound move through matter?
Sounds is a vibration that moves wave. It moves through matter as a longitudinal wave. Sound can move through gas, liquid and solid, but certain materials propagate sounds better than others. The vibration of particles transport the sound vibrations as a wave. Some materials (mostly solids) will not do this very well. Sound has to have a medium (the matter) to move through. It can not travel through a vacuum.
The matter the sounds moves through effects the sound waves. The density and pressure (and temperature) effects the speed of sound in the matter. That means that sound moves through cold and hot air at different speeds. This is unnoticeable at short distances. If the matter is in motion when sound moves through it has an effect on the sound. For example sound moving through windy air. Depending on the direction it may attenuate more or less compared to non windy air. Also the viscosity of the matter affects how fast the sound attenuates.
By: Iiro Sivula, Janne Järvinen & Hester Verwej
References:
ftp://cm.bell-labs.com/cm/amg/Physics_Com_wFig.pdf
http://astarmathsandphysics.com/o-level-physics-notes/o-level-physics-notes-the-telephone.html
http://www.connected-earth.com/Learningresources/Howitworks/Telephone/Howthetelephoneworks/index.htm
http://en.wikipedia.org/wiki/Telephone
http://electronics.howstuffworks.com/telephone.htm
http://en.wikipedia.org/wiki/Microphone
http://en.wikipedia.org/wiki/Sound
http://en.wikipedia.org/wiki/Telephone