The principles of operation of the ampermeter and voltmeter are based on the same, namely, on interaction of magnetic field with electric current, however there is a number of the distinctive features allowing to measure either current, or tension.
It is required to you
- The computer with the connected Internet, the textbook in physics.
Instruction
1. Read in the textbook in physics the basic principle used in electromagnetic measuring devices. It is known that it is based on interaction of magnetic field of a permanent magnet with magnetic field of the coil which is reeled up on a wire frame. The coil with winding is located in the constant magnetic field which is uniform besides. The wire frame is capable to rotate around some axis. The spring is attached to the coil, returning turn of a frame and all coil in initial certain situation which is established as zero. Current moves on the coil by means of the brushes connected to an axis of rotation of the coil.
2. Ponder what processes happen when on the coil the electric current proceeds. In lack of current the magnetic field enveloping the coil does not interact with it in any way. When the ampermeter turns on in a chain, rounds of winding form actually magnetic field which enters interaction with magnetic field of an external permanent magnet, bringing to turn of all frame on some corner. The angle of rotation is determined by a condition of equality of elastic force of the spring and Ampere force operating on winding from the field. The fact is that at rotation of the coil the Ampere force gradually decreases, and elastic force grows. At some point these forces are compared in size, and the arrow of the ampermeter stops on a certain value which you can observe on an ampermeter scale.
3. Pay attention that voltmeters work by several types of schemes, each of which is used in various situations. However there are classical principles of action used almost in each device measuring tension. To measure tension on any site of a chain, it is necessary to create the same tension on the site of a chain of the voltmeter. However, as we know, at parallel connection to the site of a chain of other element the current through this site becomes less because the general current branches on two components, one of which passes through the explored site, and another – through the connected element. Thus, connection of the voltmeter distorts the object of measurement. It causes the fact that resistance of the voltmeter is tried to be made the biggest.
4. At course of current through a voltmeter chain, first, on it a certain tension which can be learned by a comparison method, and secondly falls, the current proceeding through a voltmeter element can create a certain impact, say, on any magnetic element. From here also the main ways of the organization of voltage measurement by the voltmeter follow.