Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Magnetic fields used in the invention of the telephone

  1. Nov 14, 2006 #1

    here's what i have. this does some what explain how magnetic fields were used to invent the telephone? im not sure what else to put.

    "In 1977 Bell patented a telephone that uses an electromagnetic transmitter. This invention works similarly to the variable-resistance transmitter (described in part A), but uses an electro-magnet and not acidic water. This invention consists of an electro-magnet using permanent magnet, a battery, a plate of iron or steel for use as a diaphragm (or any material capable or inductive action), and a call ball. The main feature of this invention consists in the armature of the receiving-instrument being vibrated by the varying attraction of the electro-magnet which vibrates the air in the same manner at both the receiving and transmitting end of the telephone. The magnet is coiled at both ends (which end is a pole) and is positioned as close to the plate as possible, without actually touching.

    When a person speaks into the mouthpiece, the iron diaphragm vibrates with the voice in the magnetic field of the pole, this excites the currents in the coil. These currents travel through wires to another telephone. This subsiquently effects the magnetism in the pole of the receiving telephone, and makes the armature vibrate with makes the sound of the original voice. "

    does that pretty much make sense? and get to the point?

    any input is appreciated!

  2. jcsd
  3. Nov 14, 2006 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    The vibrations in the air, which come from the voice, cause vibrations of the magnet, which produces time varying potential, which induces pulses (time varying currents) which are then transmitted over wire.

    At the other end, those pulses (time varying currents) cause a similar magnet to vibrate, which causes a diphragm to vibrate, which cause vibrations in the air, which our ears 'hear' as sound.

    That was then. Now the pulses are transmitted as light in many cases or as radio waves in cell phone/wireless systems.
  4. Nov 15, 2006 #3
    thanks Astronuc :)

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook