physics question #92
Tim Seeburger, a 16 year old male from the Internet asks on November 23, 1999,Q:
How does an analog ammeter works and how could I make one?
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An ammeter measures the electrical current in a circuit. It is measured in amperes (amps). The principle of operation of an analog current meter is based on Lorentz Force. Any current carrying conductor produces a magnetic field around it proportional to the amount of current being carried. When you place a current carrying conductor in an externally applied magnetic field (say for example using a permanent magnet) there is an interaction between the field of lines from the P-Magnet and the magnetic field produced by the current carrying conductor. This results in a relative mechanical force between the magnet and the current carrying conductor. If you fix the magnet (mechanically) then the current carrying conductor deflects due to the force. If you fix the current carrying conductor then the magnet moves (or deflects) due to the force. The former case is called a moving coil ammeter and the latter case is called as moving iron (or moving magnet) ammeter. This mechanism was studied and perfected by the French scientist D'Arsonval and he brought out a meter mechanism which is still being used by all analog meters. It is called D'Arsonval movement. Check out the following websites: Lorentz Force: http://home.a-city.de/walter.fendt/physengl/lorentzforce.htm Introduction to meters: http://www.vvm.com/~radioray/html/e101-20.htm Perhaps the information from the second site can be used to construct a meter for demonstration and fun.
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