How does the Telephone Work?

When a person speaks into a telephone, the sound waves created by his voice enter the mouthpiece. An electric current carries the sound to the telephone of the person he is talking to.

A telephone has two main parts: (1) the transmitter and (2) the receiver.

The Transmitter of a telephone serves as a sensitive "electric ear." It lies behind the mouthpiece of the phone. Like the human ear, the transmitter has an 14 eardrum." The eardrum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds, depending on the variations in air pressure caused by the varying tones of the speaker's voice.

Behind the diaphragm lies a small cup filled with tiny grains of carbon. The diaphragm presses against these carbon grains. Low voltage electric current travels through the grains. This current comes from batteries at the telephone company. The pressure on the carbon grains varies as sound waves make the diaphragm vibrate. A loud sound causes the sound waves to push hard on the diaphragm. In turn, the diaphragm presses the grains tightly together. This action makes it easier for the electric current to travel through, and a large amount of electricity flows through the grains. When the sound is soft, the sound waves push lightly on the diaphragm. In turn, the diaphragm puts only a light pressure on the carbon grains. The grains are pressed together loosely. This makes it harder for the electric current to pass through them, and less current flows through the grains.

Thus, the pattern of the sound waves determines the pressure on the diaphragm. This pressure, in turn, regulates the pressure on the carbon grains. The crowded or loose grains cause the electric current to become stronger or weaker. The current copies the pattern of the sound waves and travels over a telephone wire to the receiver of another telephone.

The Receiver serves as an "electric mouth." Like a human voice, it has "vocal cords." The vocal cords of the receiver are a diaphragm. Two magnets located at the edge of the diaphragm cause it to vibrate. One of the magnets is a permanent magnet that constantly holds the diaphragm close to it. The other magnet is an electromagnet. It consists of a piece of iron with a coil of wire wound around it. When an electric current passes through the coil, the iron core becomes magnetized. The diaphragm is pulled toward the iron core and away from the permanent magnet. The pull of the electromagnet varies between strong and weak, depending on the variations in the current. Thus, the electromagnet controls the vibrations of the diaphragm in the receiver. The electric current passing through the electromagnet becomes stronger or weaker according to the loud or soft sounds. This action causes the diaphragm to vibrate according to the speaker's speech pattern. As the diaphragm moves in and out, it pulls and pushes the air in front of it. The pressure on the air sets up sound waves that are the same as the ones sent into the transmitter. The sound waves strike the ear of the listener and he hears the words of the speaker.

(Rated by 4 Council Members)

Whether you are listening or talking the same technology and principles are used; when you talk into the mouthpiece a thin metallic or plastic foil just beneath it starts vibrating due to the speech sounds. Beneath the foil is an electrode connected to a wire carrying an electric current; the vibrating foil introduces changes in the voltage and these changes are then carried forward as electric pulses.

When the listener hears your voice at the other end the entire process repeats itself in the reverse; the electric pulses affect the magnetic field of the receiver at the other end and the foil starts vibrating and picks up the pulses as they had been introduced at the origin resulting in a counter conversion of the electric energy back into acoustic energy or sound waves. The electric current flows into your phone set from the phone company by way of two copper wires ensuring that your phone does not stop working even though the power in your house may have gone off.

In a cell phone however the required voltage is provided by the battery in it which transmits the electric pulses in the form of radio frequency to the nearest cell phone tower which in turn transmits the signals to the cell phone exchange then to the main telephone exchange from where the process works in the reverse till the call reaches the receiver.

(Rated by 5 Council Members)

The telephone basically has to do two things using 2 wires, transmit signals and your voice. The signal is the ring tone you get. It used to be a bell that alerts you to an incoming call. Then there is a dial (now a digital push button) that is used to enter the phone number of the person you wish to speak to. When you pick up the phone you in effect operate a switch which then puts the telephone in to active state by means of a resistance short across the wires, this causing the current to flow along the wires. Once this is done the telephone exchange detects the DC current, connects a digit receiver and sends to you a dial tone which indicates it is ready for you to dial or push the number buttons. These buttons are connected to a tone generator in your phone and generates DTMF tones. Now the exchange will know who you desire to be connected to. Whilst your phone is inactive with the handset replaced, its bell or other alerting device is connected across the line through a capacitor. This does not short the line so the exchange knows that the phone is on hook – inactive. This also means that only the bell is connected electrically, so when someone calls your number the exchange sends a high voltage pulsating signal that causes the phone to ring. When you pick up the handset the switch disconnects the bell then connects the voice parts of your phone putting the resistance short on the line as described previously. This now confirms to the exchange that the phone has been answered. Now that both phones have their handsets of the cradle this is the signaling job done. You can now talk to your friend using the voice parts of your phone. The voice parts are in the handset and consist of a transmitter (microphone) and a receiver. Powered by the line the transmitter puts out an electric current which varies in response to the acoustic pressure waves as produced from your voice. This causes variations of the electric current transmitted along the telephone line to the other phone. Once these hit the other phone they cause the coil in the receiver to move back and forth, this reproducing the same acoustic pressure waves as the transmitter received from your voice. So your friend now hears what you said like you were stood next to them. This applies vice versa to you, so you have your conversation. Once you have finished the conversation, when you replace the handset the DC current ceases to flow and the exchange detects this so disconnects the callers.

It was the development of the receiver and the transmitter that was the great difficulty, something that we now take for granted.

Well if the above has had your head spinning then I ask you to think about those early pioneers of the telephone. They had to work out how to make the transmitter and receiver to vary the electric current in a perfect way so as to transmit voice. They were the ‘brains' of their day and we owe them a lot.

(Rated by 4 Council Members)

The telephone operates on simple principles. A telephone mouthpiece contains a thin metallic coating separated from an electrode by a thin barrier (today we use plastic) which connects to a wire carrying an electric current. When a person speaks into the mouthpiece, the acoustic vibrations from her speech push the metallic coating slightly closer to the electrode, resulting in variations in voltage and therefore a speedy conversion from acoustic to electric energy. The electric pulses are conveyed through a wire to the speaker on the other end, where electric pulses are converted into acoustic energy again.

(Rated by 4 Council Members)