How does a Telephone Work?

Michael Anissimov
Michael Anissimov

The telephone was created through the cross-pollination of two fields of study - electricity and acoustics. Although the invention of the telephone is usually credited to Alexander Graham Bell, many inventors were working on the problem throughout the 1860s and 1870s, most notably Elisha Gray, who filed a patent application for the same device only a few hours after Bell did. Although the basics of electricity were known by the 1830s, nobody suggested transmitting speech electrically until 1854. The telephone was finally invented on March 10, 1876. Into it were spoken the famous words, "Mr. Watson, come here, I want to see you."

A black rotary phone.
A black rotary phone.

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.

A touch tone telephone.
A touch tone telephone.

Converting speech to electrical energy before transmission is far more efficient than conveying speech through a mechanical channel, for example a metal pipe, because the walls of mechanical channels absorb so much of the acoustic energy as it travels. Well-insulated wires, however, are effective at protecting electrical energy from dispersing before reaching its destination. Electrical pulses travel at the speed of light, whereas acoustic pulses are limited by the speed of sound. In his 1627 book New Utopia, Francis Bacon referred to the possibility of a long-distance network of tubes to transmit human speech. Many historians consider this the first reference to something like a telephone. Unfortunately, he lacked the scientific knowledge to understand why this would be impractical.

Three critical developments were necessary precursors to the invention of the telephone. First was the understanding that an electrical current can create a magnetic field, and therefore mechanical or acoustic energy. This is credited to Danish physicist Christian Oersted in 1820, who demonstrated that a compass needle can be manipulated by running an electric wire over it. Second was the understanding that the reverse is possible - electrical induction - that is, generating a current by placing a moving magnet next to a wire. This insight is credited to inventor Michael Faraday in the year of 1821. The last necessary development was that of the battery, a chemical device capable of producing a continuous source of electricity. The first very crude battery was the "Leyden jar", a device for storing static electricity invented by two Dutchmen in 1746. Volta and others developed more sophisticated batteries throughout the 18th and 19th centuries.

Often considered second in impact only to the printing press for revolutionizing human communication, the telephone made it possible to connect people to others without dependency on the postal service. Every domain of human affairs, from business to daily life, was changed radically and permanently. Globally, the telephone has saved humanity trillions of dollars in communications costs. The basic design of the telephone has not changed since its initial invention.

Danish physicist Christian Oersted's demonstration that running an electric wire over a compass affected its reading was one of the technological discoveries that led to the invention of the telephone.
Danish physicist Christian Oersted's demonstration that running an electric wire over a compass affected its reading was one of the technological discoveries that led to the invention of the telephone.
Michael Anissimov
Michael Anissimov

Michael is a longtime EasyTechJunkie contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.

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Discussion Comments


I am glad to have this knowledge of how telephones work, but in the case of a cellular or mobile phone that uses a battery, can i please have a breakdown of the amount of energy required for just a call? for instance calling someone to ask if "he/she is at home"?


how does a telephone operate in the absence of a power supply?


thank you. this was very helpful!


At what voltage does a landline telephone operate?


this was useful in my project about how does a telephone work. Thanks.


this was very helpful in our project about the telephone.


what about mobile phones?


what components are require to prepare a telephone?


Update WV: Verizon is now trying to sell their antiquated (is it possible the generator on the aforesaid pole is a "Leyden jar"? ) phone set up to a company, but many citizens are protesting this due to the poorer economic assets of this company.

Now, if we study the explanation above can we extrapolate the theory of quantum physics to voice transmission over space?

Anybody have any ideas?

P.S.: The last phone outage was alleviated somewhat by having a technician climb the pole and regenerate the generator - however, Verizon stated they couldn't have technicians climbing the pole in the middle of the night. --Myra


Very interesting. Love the article.


i would like to know as to why we cannot convert mechanical energy to electrical energy with any external energy source. so that when any one speaks he or she could just charge their cell phones.


I live up a hollow in West virginia. Our phone (landbased) goes off when the electricity goes off for more than 4 hours. I asked (called six times etc. over weeks) someone who finally could tell me how the phones work here. He explained that the electric/telephone pole 3 miles down the road and on an asphalt road had a battery on it for the phones in this hollow. It was supposed to last up to 8 hours if the electricity went out. I explained that the electricity went out for five days in February as did the phone. I was told that the battery could be regenerated but there weren't enough men to do the job, even though some came from Va. to help. I was further told that the nearest town did not have the problem because they had a generator in the telephone company office there which was hooked up to the town phones. I want to know why our phones are not working on the system as many other phones do? I want to know why we don't either have back up energy from a generator or Verizon doesn't have enough men to keep the phones working in an emergency? How can I get help? The person with whom I spoke asked me not to quote him by name as he would lose his job.


I have a 1950's 330F Bakelite phone which I would like to convert for modern use at home. Are there any sites with diagram's available?.


i want to make a automatically dialling phone to a specified number, what happens when we pick the receiver of the phone, any voltage drop or a current....?


i have digital phone service through my cable company. how does that work differently than the traditional telephone?

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