# The Naked Scientists Forum

### Author Topic: phone wires  (Read 4848 times)

#### Anastasia.fr.1

• Guest
##### phone wires
« on: 13/04/2007 18:56:42 »
When you are talking on the phone how does your voice go though the wires?

Thank you
from Anastasia

#### another_someone

• Guest
##### phone wires
« Reply #1 on: 13/04/2007 19:32:38 »
When you are talking on the phone how does your voice go though the wires?

Thank you
from Anastasia

There is the short and simple answer, or there is the very, very, very, long answer - how many years do you have

I hope I am not going to oversimplify matters too much here, because I don't really know what your level of knowledge here is, so what I may be saying might be too simplistic for you - in that case, please let me know, and I will go into more detail.

The basic principle of what a phone does is simply convert sound waves into electrical waves to send over the wires and then back into sound waves at the other end.

Your voice is simply lots of sound waves - similar to the waves you see on the sea (except that you cannot see the waves, only hear them).

What you want to do is recreate the same waves at the other end of the telephone, so that the sounds the person on the other end of the phone hears is the same sound that you spoke into the telephone at your end.

What the telephone does is simply to convert the waves of sound into a voltage (a little like if you had drawn out the waves on a piece of paper, and sent the drawing by the post, but that would be too slow, so rather it converts the sound into electrical voltages that it can send down the wire).  When the voltage reaches the other end of the wire, the telephone then converts the voltages back into sound waves (as if they had received your drawing of the waves in the post, and from that drawing had recreated the sound).

The really complicated bit is when you look at how you get millions of telephones all talking to each other, and making sure that the right sound comes out of the right telephone, and to so that while laying down the smallest amount of wire that you can.  It is a little like when the post office has to take mail to the sorting office, and the make sure it gets delivered to the right address.

#### Anastasia.fr.1

• Guest
##### phone wires
« Reply #2 on: 13/04/2007 20:01:08 »
hello george

do you mean that when you talk yor voise gos though the wire and out the other end [just like a wave!]so other people can hear us at the other end.

from anastasia
« Last Edit: 13/04/2007 20:03:34 by Anastasia.fr.1 »

#### lyner

• Guest
##### phone wires
« Reply #3 on: 13/04/2007 20:33:58 »
The varying electric current flowing through a loudspeaker coil makes the cone vibrate and causes sound that you can hear. The electric currents which a microphone sends down the wire vary in the same way as the sound waves that come from your mouth. All you need is a long wire in between and some means of amplifying (making bigger) the tiny currents from the microphone so they manage to get as far as the other end and waggle the loudspeaker cone or telephone earpiece.
Magic!

#### Seany

• Neilep Level Member
• Posts: 4209
• Live your life to the full!
##### phone wires
« Reply #4 on: 13/04/2007 20:59:42 »
Yes.. This is a very difficult concept to overcome.

Simply, there is a non-electric way of this, which is not that of which you are thinking. Telephones do not work this way, but I will just tell you for your information.

Try this experiment with 2 cups and a piece of string.

Get two paper cups (or plastic, whichever is best) and make holes on the bottom.

With a loooooong piece of string (about 10-20 metres) attach both ends of the string into the hole, and tie a knot.

Get a friend.

Talk into the cup whilst your friend puts the cup on their ear.

I'm sure you may have tried this in some sort of science lesson - I sure remember doing it.

#### lyner

• Guest
##### phone wires
« Reply #5 on: 14/04/2007 00:20:45 »
Did you try it with the string slack?
And, of course, there's the problem with mobile (wireLESS) phones.

#### another_someone

• Guest
##### phone wires
« Reply #6 on: 14/04/2007 01:50:09 »
hello george

do you mean that when you talk yor voise gos though the wire and out the other end [just like a wave!]so other people can hear us at the other end.

from anastasia

The shape of the wave goes through the wire and out of the other end, but in order to be able to go down the wire, that wave has to be changed from being a sound wave to an electrical wave, and the changed back to a sound wave at the other end.

Hope this helps.

#### Seany

• Neilep Level Member
• Posts: 4209
• Live your life to the full!
##### phone wires
« Reply #7 on: 14/04/2007 01:54:11 »
Yes, short, simple, catchy, correct. What more could you want from our George?

Motto - George is always right.

#### Anastasia.fr.1

• Guest
##### phone wires
« Reply #8 on: 14/04/2007 21:50:29 »
Thank you all for the answers. x

from Anastasia

#### daveshorts

• Moderator
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• Posts: 2583
• Physics, Experiments
##### phone wires
« Reply #9 on: 16/04/2007 20:44:39 »
Sound waves are vibrations in the air, this means that in some places the air molecules are bunced up and in others they are spread out. Where they are bunched up they push on things so we say they are at a higher pressure.

the black lumps are supposed to be air molecules

In the mouthpiece there is a microphone, this coverts changes in pressure into changing voltages

These if you apply a changing voltage to one end of a wire the voltage on the other end will change almost instantaneously (the change moves at nearly the speed of light).

In the earpiece there is a loudspeaker. This converts changes in voltage into movements of a piece of card, which will cause the air next to it to vibrate, which is sound. Because it is virating in a similar way to how the microphone was made to vibrate, the sound coming out is like the sound going into the microphone - hence you can hear something very like someone's voice at the other end of the telephone.

The same principle is used for amplifying a band using a PA - you just amplify the signal much more and plug it into a very large loudspeaker.

#### The Naked Scientists Forum

##### phone wires
« Reply #9 on: 16/04/2007 20:44:39 »